Hi Guys,

I actually own a '94 4.0 XJS, but b/c it has the same AJ6 model engine (and hence same head gasket flaws) as the engine used in the XJ40s, thought I would also post this same subject here, in case someone else has some insight on the problem.

In a nutshell, was driving my Superblue (130K miles) down the road here a few weeks ago when she seemed to suddenly start missing on a cylinder or two, esp. when idling. I assumed at first it was possibly a spark plug wire that had worked loose or possibly a spot of bad fuel in the tank. By the time I got a few miles further down the road I noticed in my rear view mirror what appeared to be a large amount of white smoke coming out the exhaust. I thought at one point, while parked at a red light, I also noticed “heat waves” coming off the underside of the car @ the passenger side. Significantly, however, the temp gauge never moved off its normal spot near the center of range. It’s possible that the low coolant level light came on (if applicable), but due to the bright sunlight that day I would not have been able to see it if it had. After reaching my destination (a bank), upon exiting same I checked the wiring and nothing appeared to be loose. I went on a couple of blocks more to a nearby discount store where I shop, although the engine seemed to be running a bit rougher by then. When I came out of the store, she started up, but it was then that I definitely could see a large cloud of white smoke/coolant coming out of both exhausts. I called a couple of tech buds of mine to the scene, and after they arrived they were a bit puzzled at what was wrong, and tried retightening all hoses and wires in the engine bay (practically), which took up quite a bit of the remaining day. Nevertheless, those efforts were in vain. By then it was dark enough outside that my low coolant level light could be seen (not sure if it was already on, or came on at the time). They checked the coolant level and it was at least “almost a gallon” low. Up until then, I had very scant loss of coolant with her. Anyway, I called and had her towed home. Just last night, I finally got around to having a tech friend of mine come to my house and do various tests/inspections on her, suspecting a blown head gasket. Here are the results (the following is my actual post to the XJS forum):
O.K., here we go with the detailed test results, and boy are they rather “schizophrenic” (no offense to anyone with that disorder) as far as pointing to what is precisely wrong and where with Superblue’s engine:

(btw, cylinders are #ed from the front of the engine back toward the firewall)

1- engine combustion leak test (gases in the cooling system) - RESULT: positive color change of test fluid (= blown head gasket)

2- fuel injector test - RESULT: disconnection of current to injectors w. cylinders #3 and #6 cause very appreciable diminution of engine running. disconnection of the remaining injectors cause some dimunition of engine running, but to a lesser degree than w. #3 and xj6

3- compression test (dry) - RESULT: cylinder #1 - 165 lbs. #2 - 150 lbs. #3 - 175 lbs. #4 - 175 lbs. #5- 150 lbs. #6 - 175 lbs.


4- Examination of plugs/bores - RESULT: the plug in cylinder #3 was bathed in engine oil equally all over its outside; the plug in cylinder #4 had what appeared to be a thick white ring of calcification (from burning water/coolant?) near its top, just below the sealing washer. No coolant or other “wetness” could be observed in any of the bores. Remaining four plugs showed signs of usual/normal wear/use.

5- Examination of engine oil and coolant - RESULT: neither one shows signs of the other in it … examination of the coolant below the radiator fill w. the engine running shows no “bubbling” or other signs of gas being released into it.

Interesting that, after the plugs were cleaned up and put back in and coolant topped back up, the engine began running normal and smooth again. No steam/white smoke out the exhaust. After full warm up and trip of about 15 minutes driving and return, engine began missing again as before, w. noticeable steam/white smoke out the exhaust. Check of coolant level showed a small amount of loss.

My tech is scratching his head as to these results (as am I) On the one hand, the combustion leak test seems to indicate there must be a leak in the head gasket (or cracked block?) somewhere … Yet all the compression test readings are generally normal and there is no bubbling of the coolant, nor comingling of engine oil and coolant. Yet, how is the excess oil getting into cylinder #3 and coolant/water (apparently) into cylinder #4, despite normal comp. readings?

Strangest of all, tech reports that after he shut down Superblue after the testing, he waited about 15 minutes and went to start her up again. BION, she was running smoothly again w. no water/steam out the exhaust. wth???

Talk about “Jaguar Demons” … smh …

O.K., guys, what do you think? (and please dont’ say, “sell it and get another Jag”)

/ / / / / /

Not sure why the server did that, but, as to “2- fuel injector test”, that last line should have read “than w. #3 and #6”.

As to the line about Jaguar factory specs at to acceptable compression range, you have to use that “slider” at the bottom in order to view the entire line.
Anyone on here have any ideas/thoughts/suggestions?

 

Hi AttyDallas,

I responded in your XJS thread.

Cheers,

Don