Landrover Discovery 1

REPLACING A Catalytic Convertor on a 1997 Land Rover Discovery

This post is to help anyone with a Land Rover Discovery I with the GEMS engine management system.

One may have a check engine light on. Upon OD II code scanning one may find a P0420 Catalyst System EfficiencyBelow Threshold and a Bank 1 or Bank 2 suffix.

Bank 1 will correspond to the side which  spark plug 1 is located which is on the driver’s side on a USA export model.

Bank 2 will be on the Passenger’s side on the USA models.

For UK models I am betting that if you stand in front of the truck and look forward toward the truck into the engine compartment  the

right hand side of the engine will be bank 1 and the left hand side will be bank 2.

A replacement catalytic convertor will price in at about $2,100 from the Land Rover Dealer in Livermore, CA. This is for the real part. In 2009 recession in full swing and for a 1997 Land Rover – one can get an aftermarket part from Atlantic British for about $700 shipped to California.

I did install a new Catalytic Converter from Atlantic British in Nov if 2008. This unit lasted less then a year and so I replaced it under warranty with a similar unit from Atlantic British. The tell tale signs are the Check Engine light coming on with the above mentioned code.

And, once can look at live engine statistics with the code scanner. When working properly and the catalytic convertors are above 600 degrees and the O2 sensors are good and working properly, the sensor (2) on banks 1 and bank 2 will read very low. This is OK. The low reading means the catalytic converters are removing/burning conbustible products. If the 2nd oxygen sensors have voltage oscillating from 0.000 to .9999 or so volts then the catalytic convertors are not scrubbing the exhaust and need to be replaced.

When you see the first upstream O2 sensors going from 0.000 to .9999 volts and the downstream sensors (2) doing the same thing – then the catalytic converters are ineffective and need to  be replaced.

The GEMS system compares the upstream O2 sensor readings with the downsteam readings. If the downstream readings match the upstream readings, then the catalytic is deemed inefficient and the Check Engine light is lit.

From practical experience it seems to take about 3 to 5 trips of high speed and low speed for the GEMS engine management system to make a determination of a bad or innefficient catalytic converter response.

How to change the catalytic converters:

The catalytic convertors are a one piece unit. They are attached to the right and left manifolds via 3 nuts per side. The converter assembly is then attac hed to the muffler via a self sealing clamp with two bolts holding the clamp onto the muffler.

Preparation for removal:

This is assuming the shade tree mechanic in the garage

  1. Jack up the rear of the truck as far as possible. Use jack stands to hold it up. Or, any safe method.

  2. Put card board under the truck to soak up grease, oil and dirt.

  3. Assure the truck is jacked up safely as your life is on the line under the truck.

  4. Soak the manifold bolts with WD-40 or similar.

Removal of unit:

  1. Remove the two bolts attaching the catalytic convertor to the muffler. IF these are rusted and you snap them, no worries. You can buy them almost anywhere. Use fine thread bolts and nuts. Use a 17mm metric deep well socket and a 17mm wrench.

  2. Remove all three nuts on the exhaust manifold on the passenger’s side (USA) – driver’s side (UK). These are hard to get at. You can use a 10mm socket with a few extensions. Position the extensions next to the differential and you can get them straight up for one of the nuts and hit the middle one and remove it. For the remaining nut, you may need to use a short extension and get your hand up there and guide the wrench onto the nut.  If these don’t come off easily keep spraying on Wd-40. Tighten then loosen, then tighten. When they get tight coming off, then reverse direction and actually  tighten them for a small amount, then loosen.  back and forth. Hopefully, you can get then off without breaking a stud. I did break a stud and had to get a stud remover to remove it. If a stud breaks, you probably need all new studs anyway. I replaced all the studs.

  3. The driver’s side (USA) passenger’s side (UK) is easy to access. Use a long extension and work them off carefully. Only take off 2 nuts.  Leave one one NUT.

  4. Replacing studs – once all the studs are out – get a threader and rethread all the holes. Use a stud remover to put in the new studs  and tighten them up. You can get new studs from Rimmer Brothers in the UK. Get new nuts too. It can take three weeks for an order to come back to the States from Rimmer Brothers in the UK.

  5. You will see a structural bar in the way of you removing the Catalytic converter assembly. Take off (4) 17mm bolts/nuts holding this bar up to the frame. Two nuts/bolts per side. When the nuts / bolts are off, the bar will just rotate down.

  6. remove the last remaining nut from the catalytic converter on the driver’s side (USA) passenger’s side (UK).

  7. Remove the 2 oxygen sensors on the downstream end – toward the back. Use a 17mm wrench and just unscrew them. No need to disconnect them.

  8. Pull the whole assembly back a bit until the front O2 sensors are exposed and unscrew them.

  9. Remove the whole assembly by pulling it back and down.

Installing the new catalytic converter.

Installation is of course, harder than removal.

Hard part is how to line up exhaust gaskets. I choose to tape them onto the flanges of the new unit with scotch tape. This is not a great way to do it.  This will work if you don’t jostle the unit too much trying to get it back on.

This is how I did it. Of course, results for you may vary.

  1. Position the unit under the Rover.

  2. Tuck the front flanges up into the engine area where they will be going. But, not too far. Keep room for access to the front O2 sensors. At this point, it will be a good time to install NEW O2 sensors as it is a lot easier with the Catalytic converter unit in this position.

  3. Install the front upstream O2 sensors.

  4. Slip the unit further up into the engine carefully and getting the flanges ready to be slid up vertically toward the manifolds.

  5. Couple the catalytic assembly to the muffler joint. Assure the flanges are lined up. Line up the coupler collar with the muffler, install the bolts and just hand tighten to leave some slack and movement in the joint.

  6. Begin to install the flanges on the catalytic converter to the manifold. the studs will probably not line up and will be too far forward. Use your legs and press back onto the muffler to move the whole assembly back. As you are pushing back, note the alignment of the holes in the flanges in relation to the studs. Push hard on the muffler and once the studs align move then up into position.

  7. Once the studs are positioned on one side, put on only one nut to hold the assembly up.

  8. For the other side, push on the muffler again and line up the other side and put on one nut.

  9. Raise the suspension bar which was lowered previously and install one of the 4 bolts to hold the bar back up to get it out of the way.

  10. Install the two downstream rear O2 sensors.

  11. Put on the rest of the 4 nuts holding the flanges onto the exhaust manifold – put them on finger tight.

  12. Tighten the all three bolts now on each side of the flange. Use the 10mm socket and extension to access. Tighten the middle bolt a bit, then the two side bolts, then the middle again. Suddenly, the nuts will become very tight. Do not keep tightening as the stud may snap.

  13. Go around all the 10mm bolts on the flanges again to assure they are all uniformly tight.

  14. Go to the back flange which attaches to the muffler. Make sure the joint is lined up and equally tighten the upper and lower bolt/nuts.

  15. Put the remaining three bolts/nuts into the suspension bar and then tighten them all up.

  16. Make sure the truck is in park. Make sure the emergency brake is on. Open the garage door and start the truck.  Listen for leaks. If a leak is heard, then try to tighten the area leaking. I did not need to re-tighten. There were no leaks the first time through.

  17. Once all sounds good, remove the jack stands and lower the truck down with the jack.

  18. Note:  After a few weeks of operation – it would be a good idea to check and re-tighten the bolts on the flanges to the exhaust manifold if needed.

Notes on readings from code scanner:

Catalytic Converter operation can be observed with a code scanner which can read the live date steam via the OBD II interface.

Initially upon new installation of the catalytic converter, the readings from teh 2nd O2 sensor – the downsteam sensor that measures catalytic converter efficiency can be  bizarre.

When the catalytic convertor is cold – one of the sensors stays steady around .9999 volts.

After 5 to 10 minutes, both downstream 2nd O2 sensors read very low – less then .1 volts.

At no time, do the 2nd sensors osciallate up and down like the primary 1st upstream sensors.

This Discovery has a long term fuel trim of 7.0%.

This seems to mean that the Discovery is having to try to put in more fuel then is mapped via the GEMS computer/controller’s engine map.

This can be due to:

  1. 1.Air leak downstream of the MAF sensor.

  2. 2.Fuel Injectors partially clogged or plugged.

This Discovery currently has 136,000 miles on it. Any comments or readings from your Land Rover Discovery would be appreciated.

REPLACING HEAD GASKET 1997 Land Rover Discovery I

Head gasket replacement adventure.

Land Rover Discovery  I 1997.

Symptoms: Antifreeze usage. Needed to add antifreeze every few weeks – about two pints of fluid. Antifreeze leaking onto garage floor – from connections on radiator.

Symptom 2: Upon oil change at 133,xxx miles – oil very dirty and brass/copper metal filings.

Oil changed and Barr’s leaks added to the coolant. Upon addition of Barr’s leaks – all leakage stopped. This allowed some time to decide what to do.

After a few weeks, decided to change the cylinder head gaskets.

Parts needed:

Correct head gaskets – Elring is the OEM manufacturer. Made in Germany. Zylinderkopfdichtung 916.059 Mot. EFI, 3,9 l, 4,6 l V8, Range Rover, Discovery 1989-> Eingau nur durch geshultest Fachpersonal

Valley gasket (1)

Valley gasket end gaskets (2)

New head bolts – stretch bolts.

You will also need a torque wrench. To remove the cylinder head bolts – you will need a 1/2″ drive 5/8″ socket – this will equate to a 15mm socket size with a little more of a fit to the bolt. The socket should be a black inpact type of socket. Also – a universal angle 1/2″ socket drive universal joint will be needed to remove the rear cylinder head bolts.

Gasket remover spray will be needed.

A razor blade type of gasket remover – but care is required to use this on aluminum surfaces.

To remove the intake manifold – one will need a 1/2″ socket on a universal joint to get out the intake manifold bolts – some of which will be hard to remove due to limited space.

At least one gallon of Prestone OAT based orange Antifreeze

Time required:

Changing two cylinder head gaskets took me 36 hours the first time through.


A lot of equipment in the engine compartment needs to be removed before one has enough room to get the job done.

Removal of parts:

  1. First, drain the coolant. Remove the black radiator access plastic bolt using a crescent wrench. Use a plastic hose and push the hose far down into the radiator. Syphon out the coolant into a bucket. About a gallon or more will exit. Make sure as much coolant is removed as possible or else when the manifold is pulled, coolant will go all over.

  2. Remove the air cleaner top unit by unclipping all the clips. Unclip the electrical plug by pressing IN on the solid silver retaining clip and then as pressing – pull the connector off.

  3. Remove the MAF sensor – unclip from air cleaner and loosen the clamp to the plenum. Remove the electrical connector by pressing in on the wire retainer and pull off the connector. Remove the MAF and set aside.

  4. Remove the plenum chamber. This is the square box that has 4.0 on the top of it. You will need a hex socket to remove the 6 hex bolts on top. Then, flip the unit over towards the driver’s side and remove the throttle cable by taking out the small pin. Then, put the pin back in to safe keep it. The throttle cable is then removed by pressing back on the tabs holding the round adjustment screw into the metal frame. This is hard to do and takes patience. Use a small screw driver to press the tabs in. Too hard can break them.  Disconnect the transmission load sensing cable. Just move the clip to disconnect it. Then put the clip back to safe keep the clip. Remove the retaining bolt on the INSIDE facing the end of the cable. Pull the cable thru and move it away and tuck it down for safe keeping. Remove the two small coolant hoses to the pre-heater on the plenum. Loosen the clips and pull the hoses off. Note where the hoses go. One goes to the radiator – the outer of two connections on the top. The other hose goes to the intake manifold nearby. Remove the two cables from the sensors – the throttle positioning sensor and the idle motor. Remove the black injection hose which comes from the valve cover. Then, remove the plenum and set aside.

  5. Remove the rubber hose air tube from the left side valve cover and from the intake manifold.

  6. Remove the battery.

  7. Remove the alternator. Use a 13mm wrench on the tension pulley and use a larger wrench intertwined with the smaller wrench for leverage. Take tension off of the pulleys and while holding the tension off – remove the belt from the alternator with your other hand. Remove the two alternator retaining bolts. Carefully lever the alternator away from the brackets. Remove the small wire which is clipped in via a push plug.  Carefully remove the dust cover protecting the wiring connections by squeezing each end of the dust cover or carefully pressing in one end and then the other with a small screw driver. The cover is held on by formed hooks which are in the plastic cover. Then, use a 13mm to remove the large current wire, a 10mm to remove the smaller wire. Put the 13mm nut back on the alternator.  Set the alternator aside.

  8. Remove the coolant tank. Take out the three 10mm retaining bolt/nut conbinations. Disconnect the small hose to the radiator. Disconnect the large hose from the bottom of the tank. Keep a bucket near as coolant will be retained in the tank – even after draining the system.

  9. Remove the coolant tank bracket. This is done by loosening three 13mm nuts from gaining access up thru the wheel wheel. Remove the bracket. Put the washers and nuts back on the bracket for safe keeping.

  10. Remove the Evap container. This is done by removing nuts from under the wheel wheel, disconnecting the vacuum line by pressing in on the fitting and removing the line. Remove the electrical connector from the purge valve by pressing in on the metal regaining clip and disconnecting the connector. Remove the other pipe from the evap container. Remove the container – put the washers and nuts onto the container and set the container aside.

  11. Get the air conditioning compressor out of the way. Remove the 4 bolts from the compressor and work the compressor off of the accessories mount. Put the compressor in the space created by removing the battery, coolant tank and evap tank. DO NOT disconnect any coolant lines! The lines will bend.

  12. To remove the valve cover on the right – there is a metal hose that is in the way and needs to be removed. The only way to remove the metal hose is to remove the accessories plate that was holding the air conditioning compressor and holding the alternator. Remove the 4 13mm bolts. Pull this bracket out and put aside. Leave the bolts in the correct order in the bracket.

  13. Remove the hex screw holding in the metal hose. First, remove the oil pressure sensor wire clip. Then, remove the hex screw.

  14. Remove the heater hoses from the heater core side and remove the hoses from the metal hose units on top of the valve cover.

  15. Remove the 10mm nut holding on the top of the metal hose unit. Then, remove the metal hose unit.

  16. Remove the other hose which is connected to the intake unit. You do not need to remove the other end of that small hose that connects to the metal extension hose – leave as is and remove as assembled unit.

  17. Remove the valve covers. Take out the 8mm screws – 4 per valve cover. You must use an 8mm 12 point socket with a 1/4 inch drive on an extension. This is very, very hard to find. Remove the valve covers and set them aside. Throw out the valve cover gaskets.

  18. Remove the rocker arms on each side. Get two little boxes. Put holes in the top of each box – 8 holes to hold the 8 push rods. Loosen the 15mm bolts on the rocker arm unit – starting with the outer two bolts, then the two middle bolts, then the outer. Pull the push rods out and put them into each box – into the holes in order and label the box left or right and front and back. Put the rockers in a safe place. Put a rag under them as they will leak a lot of oil. Put the 15mm bolts away with the rockers. Put the rocker arms in a positional arrangement matching how they came off the truck. right rocker in the right side, left on the left side. Then, carry them back to the truck to the correct side as they are visually sitting on the floor, bench or whatever. Or, use a tag to label them.

  19. Begin to remove all wiring from the intake manifold. Remove the 8 fuel injector connections. Push in on the retaining wire clip and as pushing in – pull up. This can be difficult. Remove the sensor from the fuel rail and remove the brown temp sensor. Remove the small sensor with one wire near the thermostat housing.  Remove the thermostat housing to gain access and best to put in a new thermostat and gasket later.

  20. remove all the 8mm retaining bolts on the wiring harness. There are two per side.

  21. Remove the 10mm bolts holding on the ignition coils. There are two bolts per side. Take care not to drop them. You can put a piece of shop towel onto the socket and then press the socket onto the nut and that will keep the nut in the socket for safe removal.

  22. Make labels for the spark plug wires. 1 to 8. Cut the labels out of the paper from your printer. Use scotch tape and put each label on to the spark plug wire. The number 1 wire is on the right side of the truck in the front. – standing in front of the truck and looking back into the engine. Wire 2 is then on the front left side. Wire 3 is then the next one back on the right side and so on.

  23. Remove the spark coil unit. This is difficult as the unit gets stuck on the fuel rail.

  24. Begin to remove all 10 bolts which hold on the intake manifold. Begin with the outer bolts on the edges. Remove those and then work your way in. There is actually a diagram – see further down in this post of how to tighten the bolts. Go in reverse to remove them. Safe to work from the outsides in. The two front bolts are LONG. Make note of this.

  25. Remove the fuel connections to the fuel rail. Make note – these will drop fuel out. Have rags handy. Use a crescent wrench and another wrench to get them off. Note the “O” rings. Do not damage these.

  26. Count the manifold bolts – if you count 10 of them out, then you are ready to try to remove the intake manifold. Pull it off carefully and not it will dump out gasoline if you tilt it favoring the fuel line connection side. Take the intake manifold and dump the gasoline into a safe disposal place or into your lawnmower or tractor.

  27. Time to remove the exhaust manifolds. Use a 13mm 12 point socket to remove them all. You will need a small extension for some of them. If these are hard to remove, do not force them out. Use a lot of penetrating oil and let them soak. Then, take the bolts in, then out, then in a bit and then out. Do not use excessive force or you will snap the bolt and increase the complexity of the job. You may remove the three bolts on the bottom of the exhaust manifold to remove the manifold. The right manifold is easy to remove as you can access the three bolts from the bottom. The left manifold takes a lot of time to remove the three bottom bolts from the bottom. This manifold can be left on and wired back. Or use bungee cords to pull it away from the cylinder head.

  28. Begin to remove the bolts for one of the cylinder heads. Important to only remove the outer bolts at the far edges first. You will need a 5/8 socket which is more snug than a 15mm socket. You will need a 6 point socket – impact grade. You will need a large breaker bar, a few extensions and a pipe. You can use a pipe from a floor jack. Most floor jacks have a pipe that you can unbolt it 1/2 way up and this pipe works great. Use the pipe and put it inside the breaker bar and loosen the bolts one by one – working from outer bolts to inner bolts. This will almost seem impossible to budge the bolts until you get used to it. For the far back bolts you will need the extension and the 1/2 inch universal joint. Look at the pictures provided.

  29. When all the bolts are out – count them and make sure they are all out. Check for any bolts you may have forgotten. Some may be in the oil gallery in the head – covered under a pool of oil. Try to budge the head. If you can’t budge it, you can use the jack supplied with the Discovery to put between the heads and break the head free. Be very careful with this. If it takes a lot of pushing, then you probably forgot a bolt. These heads actually come off  pretty easy.

  30. When the head comes off, antifreeze will spill a bit into the V of the engine and into some of the head bolt holes. Immediately get a shop vac and suck the antifreeze out of the head bolt holes and out of the V of the engine with the vac or a rag.

  31. Clean up the head using carb cleaner and gasket remover. Or, take the head to a shop and have it rebuilt. Some people have them skimmed a bit for a better seal. I just cleaned the head and as I had good compression I did not do the valves. Check the head for cracks between the cylinders and around the valves and between the valves.

  32. Inspect the head gasket. Look at the armor that surrounds the cylinders. If this is very discolored or breached, you may have had detonation due to bad gas, bad timing or excessive carbon build up. These gaskets can fail just due to wear. My gasket did not really fail due to compression, but, I had coolant leaking in a bit into the rear cylinder on the right side – from the water jacket and perhaps just starting on the left side. The compression was still very good in all cylinders.

  33. Make sure the cylinder head surfaces are very clean. Use the razor gasket removal tool to remove any remaining gasket maternal. There will not be much. Check the liners. The liner is a thin metal jacket extending into the block. If the truck was overheated, this liner can slip down. The liner slipping down will uncover the water jacket and will cause coolant to enter the cylinder in this way. If one of your cylinder liners have slipped, then there is no way to fix this problem at home without removing the engine completely.

  34. Remove any gasket material from the cylinder block. Make sure all surfaces are gleaming silver – no grease or dirt. Use clean paper towels and use gasket cleaner to make sure they are perfectly clean. Next, use carb cleaner on a clean shop towel and wipe down all the surfaces. Allow the carb cleaner to evaporate. Some folks have said to use brake cleaner. I used carb cleaner. Note where the dowel pins are on the block to locate the head.

  35. Lay the new cylinder head gasket onto the engine block. Note the word TOP. Make sure you can see the word top. Check the oil holes and make sure those are visible and that the gasket is on correctly.

  36. Lay the head onto the block – taking care not to move it all around and disturb the head gasket. Note the two locating dowels in the engine block – get the head onto those and let the head settle onto the block.

  37. Important- use only NEW head bolts. The bolts are stretched as they are tightened.

  38. Soak the ends of the head bolts in fresh engine oil. Put thick grease UNDER the heads of the bolts – where the bolt will contact the head. This can not be stressed enough. The bolt will gaul and skip when tightening under load and not fasten correctly if this is not done.

  39. Use the diagram in this post and tighten the head bolts in order. First, torque the bolts down with the torque wrench 20NM or 15 foot pounds. Then go through again and tighten 90 degrees. Then, again 90 degrees. You will need the breaker bar and the pipe. Note – for best results – put a dab of paint on each bolt to mark one edge and use that to visually make sure you have turned the bolt 90 degrees. As the breaker bar and extension will stretch, the result using a visual whilst tightening may not be accurate and may be on the conservative side.

  40. Once the head is on, put the push rods back into the head in order. Place the rocker arms on and tighten inner two bolts, then outer then inner and then outer until snug. Then tighten the two inner bolts to 15 foot pounds (20 NM) and then the outer bolts.

  41. Put the manifolds back on. Make sure you use the correct gaskets against the manifold to head. I re-used the original gaskets. They had three of them per side all put in there. Worked just fine. Note – re-tighten the exhaust manifold bolts after a few weeks of driving.

  42. Put on the new valley end gaskets. Put on the valley gasket. Make sure the valley gasket lines up perfectly with the intake ports on the heads. Put the retainers on at the ends of the valley gasket and tighten to spec. See attached picture of procedure later in this post.

  43. Set the intake manifold back onto the engine. There is a very specific procedure of tightening all the bolts and retainers. It must be followed. This has been revised from Land Rover and the actual intake valley gasket has also been revised. See diagram in this post.

  44. Put the spark coils back onto the engine.

  45. Reconnect the fuel lines.

  46. Now, reverse all the steps above.

  47. Fill the coolant system with a 50/50 mix. I use OAT based orange coolant – Prestone. Use distilled water or use premixed coolant. Do NOT use GM orange from General Motors itself! Only Prestone. I don’t use green silicate based coolant.

  48. Turn on the key – on and off on and off. Let the fuel pump run and take out all the air from the fuel system.- until the fuel rail fills up and all the air goes back to the fuel tank.

  49. Carefully start and run the Rover. If all want well, it will just start right up.  Keep adding coolant. Turn on the heater. Drive for about 5 minutes, put in more coolant. Drive for another 5 minutes put in coolant. Then check after a few hours. Then after a few days. The system will self bleed. No need to bleed it.

  50. Now, change the oil as there is probably junk in it left over from all the work.

  51. Enjoy your “new” Rover. If all is well, there will be no more oil leaks than you had before. There should be no pressure from the coolant tank indicating a blown head gasket. On the Discovery 4.0, pressure would more likely be a breach from the rear cylinders into the coolant jacket at the rear of the head or block. Or, a cracked head causing pressure or a slipped liner.

Here is a summary of the Head Gasket job which I first posted on

jfall (2009-05-16): I want to thank Erik for creating his board and keeping it running. I do agree with Erik that Land Rovers are worth the time to keep them properly serviced and if so, will last a long time. I bought a brand new Discovery I in December of 1997 – as such this is a 1997 Discovery.
Truck has gone from 1997 until May of 2009 with no real issues until now.
I took the Discovery to Land Rover of San Jose and for the first major service – I was charged $1,200. I figured that was pretty high, so after that all the work myself.
In California, I learned, when you take a car to most garages for a Land Rover – the goal seems to be to charge at least $1,000 to the customer get the car back, for whatever reasons. Profit goals or such.
As many folks are casting horror stories about their Land Rovers I can say – this has been a very good value for the money.
The Discovery now clocks in at 133,000 miles.
I always change the oil around 3,000 miles and have always put the regular cheap gasoline into the truck.
When I first had the truck, I took it to the dealer to fix a gas gauge problem of the gauge not registering any fuel.
The computer in the Disco was reprogrammed at no charge in Vancouver, Canada when I was visiting that city and country from the States.
At around 50,000 miles the truck would miss at speed. No codes. For a cost of $1,200 a garage local to San Jose replaced an O2 sensor and a speed sensor and that cleared up the problem.
At around 80,000 miles I replaced all 4 O2 sensors to gain better milage and avoid problems. I also replaced a working fuel pump assembly – that had not gone bad yet.
From that point – 80,000 miles to present – 133,000 no real breakdowns ever or problems. I did notice a gradual loss
of coolant and would refill the coolant tank.
At around 129,000 – alternator noise. Replaced the alternator with a brand new alternator bought from British Pacific. This was a new Denzo for $299 and the recommended replacement.
I did find there are leaks from the radiator where the
oil cooler pipes come into the radiator – antifreeze leaks out from the retaining bolts on the radiator fittings.
I read about how Dex-cool will help aluminum survive and as I figured the whole engine and heads are aluminum, I put in Dex-cool by Prestone at probably 50,000 miles.
Interestingly, at now 133,000 miles – the original water pump is still in there. No play in the pulley. I pretty much changed out the Prestone Dex-cool every two years.
Probably from 128,000 miles to currently 133,000 miles
lots of water used by engine and filling the tank. last few months – 131,000 to 133,000 probably a large beer glass of water added to coolant tank every two weeks.
Finally, I added Barr’s leaks and the coolant usage pretty much stopped. I kept Barr’s leaks in for a few weeks and then changed the oil.
When I changed the oil – I found a lot of copper or brass in the oil and suspected coolant had gotten into the oil.
This put me into panic mode and parked the truck in the garage and started to pull the engine apart. Removed the
intake manifold and found the valley gasket to be crusty but no obvious leaks. Removed the passenger’s side cylinder head and found back most Cylinder was looking pretty crusty and valves looked black as others looked white. Thinking the back of the head gasket was allowing some coolant into the cylinder. But, all in all the gasket was a lot better looking then I would think at 133,000 miles. I pulled the other head on the driver’s side and that gasket was even better – almost new looking. I had bought new head gaskets from British Pacific – after they assured me that these are the correct gaskets. And, they are – same vendor as the original Land Rover Discovery gaskets.
So, I put on the passenger’s head first – torque to 15 foot pounds. Follow diagram and then 90 degrees all around and then 90 degrees again. For the last sequence – you need to take a large pipe and tighten it.
I had problems with one bolt – it would skip and catch when intalling it. I attribute that to not enough oil on the bolt before I put it in.
I did the driver’s side head the next evening. Soaked the bolts in a pot full of Mobil 1 synthetic.
I have never had much luck with head gaskets, so the outcome will be interesting.
There was a lot of carbon in the cylinders and on the head, so I removed all that.
I have yet to put the intake manifold on and I will follow a TSB out – that tells of a 4 stage tightening sequence.
I’ll put some Hylomar on the water jacket parts of the intake valley gasket.
So, I am hoping the Discovery will go back together. I am not a professional mechanic and did not get my cylinder heads shaved or valves redone. I just want to get 30,000 more miles from the engine – or one to two more years.
This 1997 Discovery – leaks all over the floor. I just park it on cardboard. I don’t really care about all those leaks.
As long as I top the oil. I need to top the transfer case as I have only changed that oil once. I have changed the diffs a few times in the past and have drained transmission oil out probably every 30,000 miles – about 4 quarts and put in new fluid to keep it sort of fresh. So, I have not replaced the filter in a long time.
At around 127,000 I replaced the catalytic converters with such from Atlantic British. The stock rover converter was to cost $2,200 for just the part from Land Rover dealer in Livermore, California. For about $500 delivered, I had an aftermarket. I installed that and reset the Check Engine light with a code scanner and took the truck in for emissions testing. It passed.
Now, the light keeps coming on – Bank 1 emissions efficiency problem with cat convertor.
Researching what can make a catalytic converter go bad -too rich mixture – I seem to have that from pulling the heads and seeing all the carbon. And, the code scanner says my Long Term fuel trim is 8% instead of 0, so the ECU is dumping more fuel into the engine for whatever reason.
I figure- antifreeze was burning in cylinder 8 and maybe a bit in cylinder 7 and maybe that destroyed the new catalytic converters. Or, too rich fuel.
So, after putting the engine back together and if the newly installed head gaskets are fine, then bypass the throttle heater *as advised on this board – thank you for that*
and I will replace the O2 sensors and see if the long term fuel trim improves on the code scanner. And, put in the Prestone Dex-cool again (never GM Dex-cool)- I was running Dex-cool at about 70% Dex-cool to water for protective properties but maybe not smart – will go to 50/50
So, I feel it will be a miracle if the truck runs again. It wsa running perfectly when I took it apart, but was running on the graces of Barr’s leaks and it had antifreeze in the oil. Thinking Valley Gasket – new gasket will solve the water in the oil issue. Best of luck to all readers. Yes, other brands are more dependable or not. But, I feel the Discovery I is quality built.
I keep hearing nightmares about Discovery II (1999) from this board. Thank you Erik and all for posting.

jfall (2009-05-20): My 1997 Discovery went all back together after head gasket replacement. I forgot to put in the Valley Gasket end gaskets. I just put Hylomar on the engine lip and the valley gasket is right on that.
I do now have a very small oil leak which is dripping on the Drivers side (USA drivers side) from the engine. One drop every minute or so. Just enough to make a horrible smell at a stop light. There is a downward flange or casting on the engine and it is dripping from there.
Used a mirror and can’t find a leak yet.
So far:
1: Coolant leaks all eliminated by soldering the radiator ports where the oil and transmission coolers are.
2: Seems not to use coolant or put coolant in oil now. Still under observation.
3: Less oil on the ground.
Watching coolant levels every day and engine oil level and color.