Hi Guys,

.In a nutshell, was driving my Superblue ('94 4.0 / 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.
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.

 

Cylinders that have a coolant leak into them typically have pretty clean (no carbon on the) combustion chamber, piston top and spark plug electrodes. If you have an oil fouled plug, that could be rings or intake valve seal.

I have had intermittent head gasket leaks before, the gasket would leak when the car cold and stop when it warmed up. (alum head on iron block). I am sure it would have worsened over time had I not fixed it as soon as I was able

If my car had a head gasket leak, that spare Chev motor I have would go in so fast your head would spin.

Doug

 

AttyDallas,

All of that sounds fairly typical of a head gasket that has gone, and when the engine warms up is allowing coolant to pass across the split into one or more cylinders. Your symptoms are consistent with the engine running fine when cold and then leaking coolant into the bores when hot as the engine expands.

I'm presuming you also did your compression tests when the engine was cold? If you did it when the engine was hot and the gasket split open, you might well see different results.

Also, your reference to the oily plug, did you carefully check that the spark plug well wasn't oiled up? The spark plug well seals are prone to wear and the well can fill up with oil, giving a conflicting impression of the plug when you remove it.

If the gasket has gone, it's not the end of the world. As the car seems to run well when cold, there's a reasonable chance that the head isn't warped. You'll seen be back on the road!

Good luck

Paul

 

Based on all the positive reviews I have seen on YouTube for the Blue Devil sealant product (as well as being recommended by my tech and even by the driver of the tow truck that drove me home that fateful day), I'm going to give it a try. I figure I have nothing to lose at this point, since I don't happen to have spare $Ks laying around for a mechanical repair of the head gasket. In fact, I ran across a link on the forum earlier to the 2carpros.com guys' website where they mention this about it:


* * * * *
Not being a big believer in pour in solutions we had to give this product the best in market award because we have had much success in fixing certain kinds of head gasket failures. It wont cure all failures but the product works well for most available on Amazon for about $50.00 just following the directions

* * * * *

Will report back on here if it works or not.

 

Well, in a word, despite all the positive testimonials for the Blue Devil sealant product on YouTube, personal recommendations from friends, and even the positive mention of it by 2carpros.com on their website, it did not work on Superblue. After about 40 of the 50 minutes of idling following introduction of the product into the cooling system, things had still not started to seal up. Water still coming out of the exhausts, w. the temp gauge starting to climb into the red.

I had considered maybe trying a 2nd bottle to see if it might "take", or possibly going with B.D.'s "mechanic-friendly" version of the product, a bit stronger stuff that requires removal of the thermostat and flushing of the cooling system before putting in, but have decided to just pack it in.

 

BLUE DEVIL aka "Snake oil" ?????????

 

Blue Devil is NOT "snake oil" .. read up on it online, dude .. I had it recommended to me by a personal friend who is a tech, by the tow truck driver that towed my vehicle home, and others. There are tons of positive reviews for it on YouTube, and even a recommendation of it on 2carpros.com's website.

 

https://www.tornadoair.com/

Done my research.

ABC News 10, Cops, Master Mechanics, Bobby the CarClinic(tm)...all rave about it.

I'm sold?

 

The only thing I am pouring into my engines is 20W-50 oil, 50/50 coolant-anti freeze and occasionally fuel injector cleaner in to the gas tank.

 

Hi AttyDallas,

Head gasket failure on the AJ6 is very common, and fortunately, replacing it is not difficult, it's just time consuming. I did the head gaskets on my two XJ40s three times (90K miles apart on one of them). A common issue is that the aluminum in the head erodes and creates a passage for coolant to leak into the combustion chamber. Following a tip from members of the Jag-Lovers forum, I used JB Weld metal-filled epoxy to fill the eroded depression and then carefully scraped it flush to the head using a razor blade as a scraper.

While the head is off, it's a great idea to replace the valve stem seals. Also, it's also a great time to deal with all the typical oil leak spots on the left side of the engine, such as the oil filter housing gaskets, oil cooler line or bypass U-pipe O-rings, dipstick tube O-ring, etc. Also, the water rail gaskets and coolant hose that is virtually impossible to replace with the intake manifold in place. And if you've had any issues with the oil pressure sender (low oil pressure readings on the gauge), replace the sender/switch as well.

Cheers,

Don

 

Time-consuming is an understatement. I tried printing out the instructions from the Jag factory workshop literature for r/ring the head gasket, and the list of sub-procedures/tasks filled FOUR pages. Funny you mention the oil leak problem, as just a few months ago I was having a major one, and just could not pin down where it was coming from. I took her to a major chain repair shop, and the tech, after putting her up on the lift, claimed the leaks were in like 4 or 5 places, inc. the dipstick tube o-ring and the oil filter housing gasket (as well as supposedly a major leak of the oil sump pan gasket). I don't know why she would just suddenly start leaking at all those places, but, not trusting the shop, I had a tech bud of mine get under there and check all those alleged leak spots out. He said he could see no evidence of ANY leaks at the places claimed. One place she WAS leaking at was the oil pressure (idiot light) sensor, and you could even see it coming out from behind the sensor when the engine was running. However, the sensor was not loose in its mounting hole, as one would expect. I put in a new one anyway, and no more leak there, at least. I think "Motorman" on here has mentioned something about the AJ6s having a bad rep for an oil leak at the front passenger corner of the engine, near the engine # plate. My tech said he did notice a slight leak from that area while checking out the head gasket leak, again while the engine is running. What IS the source of that leak, btw?

I was thinking maybe the easiest way to untie the Gordian Knot here is just to put in another good used engine. But then, the factory workshop literature shows the sub-procedures/tasks for that job fills TEN pages.

Given all this, as well as the sky high prices for used XJSes (or even X-300s or XJ8s), it looks like, for the first time in over 25 years, I may be looking for a NON-Jaguar for my next car .. In fact, have been looking at the Cadillac Allante, which was a 2-door, 2-seat sport model GM came out with in '87-'93 to compete with the XJS and the Mercedes SL convertibles. Body by Pinanfarina (sp. ?), no less. At least no known issues with those (except for the NorthStar engine, which GM changed to in '93 MY) and, when something happens, the parts are relatively plentiful and cheap compared to the XJS. Probably easier to work on, too.

 

Motorcarman may correct me, but my recollection is that the original head gaskets did not seal an oil port well at the front right corner and developed a leak that dripped down around the distributor. The new revised head gaskets have a better seal around that port.

The Haynes XJ40 repair manual gives an excellent step-by-step procedure for the head gasket replacement. I don't even bother with the factory workshop manual. You can download a mostly complete U.K. edition of Haynes here:

Haynes Jaguar XJ40 Repair Manual

Since you would have no idea how long the head gasket or oil seals in a salvaged engine might last, the better course, IMHO, would be to repair your existing engine and enjoy it for another 100,000 miles.

If a simple blown head gasket on an AJ6 is too daunting, you would be very unhappy with any car with a Northstar V8. Any 30-year-old car is going to require significant repairs from time to time, and in my experience, over the long term Jaguars are really no less reliable than BMWs, Mercedes-Benz's, Cadillacs, Audis, Volvos, Lincolns, etc.

Cheers,

Don

 

I’m not sure anyone has seen BMWs or Audi’s as a posterchild of reliability since the 80s….

As far as parts being plentiful, would they really be that plentiful for a car that was produced for 6 model years?

I know it’s probably a lot of parts frankensteined up from other models in the GM brand, but I would bet that the Allante specific parts, interiors,ECU, body parts will all be rare and pricey, no?

 

Thanks esp. for the Haynes reference. It shows the head gasket (or head) r/r process as being quite a bit less onerous/intimidating vs. that outlined in the factory workshop literature.

 

Good point, but I bet GM sold more Allantes than Jag did XJ40s (or XJSes) during that same period of time.

 

Allante sold 21,430 cars during its 7 year run between 1987-1993

Jaguar sold well over twice as many XJS cars during the same period. 54,014 to be exact.

If you’re talking just 6 cylinder cars, XJS sold 14,901 of them.

 

And narrowing that last # (14K+) down to units sold in the U.S./N.A. = ?

 

If you like blown head gaskets and main bearings that fail, buy anything with a Northstar. Most are far more expensive to fix than the car is worth because the fixes require extensive rework and replacement of the head bolts and and main bearing studs with larger units. It's an engine out operation. Car Wizard on YouTube has done a few videos on the process, and he doesn't recommend doing it because of the cost. As a result, a lot of Allantes are junked when the engines fail. The very late Northstars were better, but still didn't completely solve all of the issues.

Jon

 

but if I add back in all the other Jaguar models that shared the same engine...

Remember, parts can be shipped internationally too, but if we're only talking engines, the XJS is only part of the equation. From 1986-1994 (just barely outside the Allante range), 208,733 XJ40s were produced...

The numbers aren't as outlandish as you think, especially when you consider a failed Northstar goes to the crusher immediately.