I need some guidance here. I have a 98 XK8 with 117k miles. It exploded a radiator a month ago. I put in a new one. A week later the reservoir tank exploded. I replaced it also. When I refill and bleed (completely) the car expels its coolant as soon as it warms up. At this point I towed it to a reputable shop. Their diagnosis is; combustion gasses leaking into the cooling system. This blows things up. They did a pressure test to confirm this. They recommend either junk the car or get a used motor. Other than the motor the car is in good shape. What years of motors will swap into this? I would like to get one as new as possible like a 4.2. Would that be a straight swap or would I new to change mounts, ecu, accessory drives, etc.. I hope I can afford it!!
Thank you one and all for any help. Will

 

Your car uses a AJ26 Engine. A direct swap would be a 1997-1998 4.0 liter non-supercharged engine.

XK8s changed to a AJ27 4.0 liter engine in 1999.
XKRs changed to a AJ27 4.0 liter engine in 2000.

 

Could the problem not be a busted head gasket?

 

I have combed through the threads on motor swaps for the XK8 4.0. Most all seem to refer to the SC motors not the NA motors. I found a 2004 4.2 complete with accessories. Low miles for a good price. What is required to swap the motors? If I missed a thread will you please post a link so I can study it?
Thanks again
Will

 

It sounds like you've had enough anxiety for now. Swapping SC for NA and/or 4.2 for 4.0 requires different control modules, sensors, etc. They are not close enough in design so that you can easily do it by simply replacing a few parts.

Just because you are getting a good deal on a 4.2 doesn't mean it'll be a good deal by the time you pay a shop to install it... and get it running dependably. I agree with Paul that you replace your motor with a 1997-1998 4.0 liter non-supercharged engine and enjoy your car.

 

Changing the whole engine seems a lot of work when all that's wrong is almost certainly a blown head gasket. Just replace the gasket.

(Does anyone know how to locate which bank the blown gasket is on?)

 

It has been reported by several professional mechanics on the forum that nikasil linings are damaged by overheating. Still, it is worthwhile removing the heads and inspecting the cylinders for damage. If not damaged the heads could be skimmed if they are crack free and replaced using 4.2 head gaskets.

There have been threads covering the installation of both AJ27 and 4.2 engines, but as Gordo says, it's not that simple. Locating a usable AJ26 from a XK8 or XJ8 would be a better choice.

And don't let anyone tell you a LS1 conversion would be more cost effective.

 

+1
Certainly worth investigating before you blow $$$ on a replacement motor. The composition gaskets on early cars apparently decompose. Can be replaced with the later MLR gaskets as used in the 4.2. HAs been mentioned in a few threads - check out this one: there's some good pics, too. https://www.jaguarforums.com/forum/x...gasket-137107/

I guess a compression test would identify the failed cylinder(s).

HTH,
Mike

 

Prob won't be cost effective unless he has access to the Lsx drive line for cheap, but if you are keeping the car long term and have $$$ to do a LSx conversion why not do it? Once complete all the drama that happens to several jag owners motor/trans and related components wise goes away.

 

Although I agree with prior posts that the most likely issue is a head gasket, are you completely confident in the diagnostic?

You have pressure in the cooling system, but normally, when the car cools, water goes back in the combustion chamber. Besides the risk of hydro-lock, have you observed any white smoke (steam) out the exhaust? Also, the cylinder with the water leaking in it is usually squeaky clean (as in steam cleaned). Spark plug should be spotless, piston top should not have any carbon deposit, etc. Also, there are some test strips around you can buy to check for exhaust traces in the coolant.

Have you ruled out any of the other (cheaper) possibilities: thermostat stuck closed, water pump with broken impeller (essentially not circulating the water, a known issue with the early cars I believe), or even issues with the fans (do they turn on with the AC?)?

Best of luck, keep us posted.

 

Many thanks for the suggestions. Regarding the exhaust gas to cooling system leak; Motor runs smooth, no smoke. Coolant coming out the vent reservoir looks clear enough. I have not tested for contaminants. I will ask the parts store if they have a test kit. Motor oil is fine, no froth or such stuff. I suppose if the gasket failure was between combustion chamber and coolant channel that would make sense, especially if the crack is quite small. When the engine warms up the crack opens. I will investigate the gasket situation further. That would be good news and I could check the tensioners while there! Members, Thanks again Will

 

Another thing: As there has been several opportunities to change the coolant fluid already, are you confident there was no mixing of incompatible types? I understand mixing "green" type with "orange/dexcool" type leads to gelling, which would clog the system and lead to overheating. Just another thing to look into.

The right answer is to find the specifications book on jagrepair.com, look up the coolant type by year (and VIN) to see what is supposed to be used (which of course does not tell you what is in there). Best of luck.

 

It would be best to gather a little information and not what he said she said. Get the compression readings per cylinder and remember this is a Nikasil engine so the compression could be skewed. You said that the oil is fine, no coolant in it? No white smoke and the motor runs smooth leads me to think twice about replacing the engine or pulling the heads just yet. If you have a coolant system pressure tester put the tester on the coolant tank and see how fast the pressure is building up and if it is pulsing. Check the obvious and that would be the coolant system for clogs check the coolant pump and the thermostat and the coolant fans first then move on to the engine head gaskets or the Block.

Let me tell you a little about my 1993 350 Silverado 281,000mi and the engine would overheat every now and then. I replaced all the hoses flushed the block and radiator and replaced the radiator cap and water pump and it would still over heat every now and then and the last then cost me $500.00 for a tow home. By accident I noticed that the clutch on the fan would lose tension and spin freely when it was hot replaced it and I am still driving the truck with no issues.

Check everything!

 

This additional info tells me it's probably not a head gasket - or even a cracked head. If there is a delay before 'she blows', then it sounds like a stuck thermostat, beggared fans, or a completely stripped cooling pump.

To find out have a coolant test (takes seconds and all garages do it for free). If there's no contamination in the coolant change the thermostat and water pump.

Must most important .... STOP BOILING IT OVER !!

 

More thanks to ya'll.
When this has over heated the gauge is normal and almost instantly jumps to the top. When it exploded the reservoir, everything had been good for two or three days. I pulled up to a stop signal and watched the gauge jump. As I went thru the signal to stop the car the tank exploded. I could see the hood of the car jump and felt it through the whole car! I thought the motor blew! As soon as the tank went the temp went back to normal, (suspect there was no coolant to be measured at that point).
I have had the thermostat bypassed for several weeks. When bleeding the air out of the system (I ran it for about 40 minutes) during this time I monitored the water temp with my lazer thermo gun and it did not get over 165°. I ran the heater and measured the heater output temp at 117°.Also during this time I observed a constant flow of coolant in the thermostat tower. When I revved the motor coolant would jump right out at a high velocity. This makes me think the water pump is doing its job. when I finally put the bleed cap on and tested the car, I only ran it an additional 5 minutes or so then turned it off. The car then puked about a gallon and a half of coolant on the floor behind the right front wheel. Fans are working properly.
I am not giving up and thanks for the input. I really like this car, but am still a pragmatist.

 

Unfortunately the gauge isn't a gauge, just a graphic idiot light. It will not show trends and only warns you AFTER its already overheating. One of Jags better ideas. To be fair some other newer cars use this also.


Dave

 

" I have had the thermostat bypassed for several weeks "

How have you done that?
Are you saying the engine ran for 45 minutes without the pressure cap on, and then puked only after the cap went back on?

 

I removed the thermostat to bypass it eliminating it as a possible problem.

 

"Are you saying the engine ran for 45 minutes without the pressure cap on, and then puked only after the cap went back on?"
__________________
Yes, i replaced the blow reservoir then refilled coolant (mostly water). I removed the bleed cap and ran the car. No thermostat. As bubbles appeared, I added more coolant until no bubbles. I then cycled the heater on high for about ten minutes. I continued to run the car while checking coolant temp with my lazer thermometer (170's) until I ran it for about 45 minutes total. I then replaced the bleed cap and topped up the reservoir. I drove the car to the end of my street and back (1/2 mile). Checked temp with thermometer, still 170's. At that time the coolant began pouring out under great pressure, just behind the right front wheel well. Maybe a gallon and a half. This pressure is just very random.

 

No, no, no....this should not be done. This car will overheat with the thermostat removed. In this engine design a thermostat must be in place to direct the proper flow of coolant into the correct channels. Put in a good thermostat before you waste more time and money.