1991 4.0 XJ6 with 40k miles. Runs really well, was leaking coolant from the coolant expansion tank seams. Replaced it with a used one from local junk yard. That one lasted a good 100 miles and then blew a leak at the seams. I JB welded the used expansion together but haven’t put the car back together yet. Now I’m thinking I might have a blown head gasket causing excessive pressure?? I could drive the car, let it sit for a week+ and then open the coolant cap and you can still hear the pressure escape.

Evidence of no head gasket failure

• Did a combustion engine block test on the coolant. The liquid did not change colors.
• Have started and let the car idle with the cap open, no gushing of water or bubbling. I do notice very tiny particles that might resemble “oil *****” might just be dirt too?
• Oil on dipstick looks fine.
• Runs really well, doesn’t overheat. Will move between Normal and Hot at idle when I’ve lost too much coolant but will move back to normal after driving. (have only ran in this state for 10-20 minutes)

Evidence of head gasket failure

• There is “milkshake” residue in the PCV pipes that connect into the Oil filler neck
• Same looking residue in one of the skinny coolant hoses that connect to the expansion tank.
• I noticed “smoking” coming from the oil filler neck with the cap open and the oil dip stick with the dip stick open

Here are some videos and pictures. Please help and advise. Its a very good condition car, does it sound/look like I will need to change the head gasket?

Please view the videos I took of the “smoking” at this link https://drive.google.com/drive/u/0/f...8Kwub11FOIEm_X


Substance in the PCV pipe that connects to the oil filler neck

 

Hello, to put your mind at ease, that "Substance in the PCV pipe that connects to the oil filler neck" is quite normal, condensation mixed with oil vapour.

"Oil on dipstick looks fine." plus "Did a combustion engine block test on the coolant. The liquid did not change color"
These are good indicators that your head gasket is probably OK.

AFAIK, the expansion tank material is not glue-able with epoxy or JB weld, others have tried and it hardly ever is successful. I believe there is a member on here that DID fix his seam-split tank and IIRC, there are photos and procedures in the archive ...do a search in the XJ40 archive for expansion tank and it should turn up ....maybe it was Jim? @manwich66

Larry

 

Thanks for the reply Lawrence, that makes me feel a lot better that jaguar people don't think its a head gasket yet.

 

The mud in the pcv tube is just oil vapor mixed with water vapor from the air

 

I found this repair thread in the archive searching for "split seam tank" - there must be others, but this one, even though not on an XJ40, gives you a general idea of a repair procedure that apparently works

https://www.jaguarforums.com/forum/x...t-tank-105518/

Larry

 

Thanks Lawrence, I was in the process of trying that to my original tank but the machine screws I bought all striped on the hard plastic, that's when I decided to get the used tank. Right now I'm going to JB weld my used tank just on the outside seams to see if that will hold, If that doesn't work maybe go back to my original tank and get the screws out and try sealing from the inside like in the thread you posted.

 

I wouldn't use screws, use bolts or rivets.

Larry

 

Another product that may be suitable is Permatex Black Plastic Welder. I've found that it adheres to most automotive plastics. I order it from Amazon.


Cheers,

Don

 

Thanks everyone for the help, so my lazy experiment of just JB welding the sides (seams) of the tank failed. I tried applying it on two different occasions too, using it liberally but it leaks from the same hairline crack at the seams. Once I get the time I will try riveting and sealing from the inside on my other leaky expansion tank.

 

That stuff that Don suggested looks like the cat's meow to me!

Larry