Expansion tank repair

Cdn '87 SIII V12 with pinhole leaks in the expansion tank.
Talked to a rad shop and they say they can fix it, solder the big holes, a first coating (?) then second coating of Red Kote.
I will pay others to repair things but am always interested in whether I can do it myself, (save money and learn).
I searched the archives and found some older references to this idea and am wondering if anyone has had additional/recent experience?

My 85 XJS had similar problem. I removed it and gave it to a radiator shop to solder a plate over the worst worn part as a repair. So…I cant answer your question directly…but…a few months later it started leaking again. The answer for me was a replacement NEW part. The inside of the tank has been corroding for decades and finally starts to leak when all the metal has disappeared from one spot. But highly likely there are several spots where the metal is microns from leaking…and a new replacement was not expensive.

I agree that a replacement is the best solution but if you really want to repair it on your own sandblast it to bare metal and then apply 2 coats of west system marine epoxy. Paint after the epoxy sets and any runs have been sanded. Larger holes will need to be soldered first. I did this on my e type header tank over 20 years ago and it still does not leak. Be aware that the rusting will slowly continue from the inside but chances are the rest of the car will rust away first.

Matt and Geoff, thanks for the replies.
I was actually thinking from the inside out.
The rad shop I talked to applies the coatings on the inside, which is how gas tanks are sealed.
The marine epoxy on the outside may be an option.
I’d love to replace it however the best I can find will be about $350Cdn (ouch)


sorry I can’t speak for the V12 expansion tank directly, but the basic problems should be identical for SII 6 cylinder cars using a metal expansion tank (or what material is the V12 tank made of?).

My PO invested in a good used replacement part that he installed in 2004. Shortly after I bought the car in 2007 it started leaking along the seams. So I purchased a new part the same year which lasted well, until earlier this year I noticed rust bubbles along the upper outside - a totally dry environment. The car has always been run with antifreeze in the coolant.

So, it seems to boil down to buying a new part and (!) treating it to additional coating both from inside and from outside. It follows from the principle of the expansion tank that it will be only 1/3 full as a rule - not good for the inside. The outside is only covered by a thin layer of protective paint, not enough I guess.

If you want to keep your car original and do without an aluminum or stainless container you’ll have to walk that extra mile to forget this issue for the next twenty years. There may be a reason beyond cost and weight saving that made Jaguar switch to plastic containers …

Good luck


75 XJ6L 4.2 auto (UK spec)

I have very successfully soldered a galvanised fuel tank - now 11 years on. Did it with an electric soldering iron - 200 watts - the type used for guttering in the old days. Expansion tank should be fine. Paul.

I have had luck with fiberglass liquid and some mesh sand the metal the fiberglass then sand and primer and paint. Just a thought and easy no expensive tools to buy!

Thanks for the thoughts on the fiberglass solution.
Last night I fired up the mig welder, dialed the heat down and spotted/filled in the holes.
I need to clean up the welds or I won’t win any awards at the car shows (not the objective) but it seems to have worked.
Next will be to rig up some plugs for the line fittings and jury-rig a pressure test at +/- whatever the cap rating is.
After that, I picked up off the internet several examples where guys have coated the inside of motorcycle gas tanks with a product called Red Kote, with good success.
One chap used vinegar and BB’s in the tank, shaken up well over a week to clean/etch the inside of the tank. it cleaned up really well.
Then he applied the Red Kote.
Coincidently, I chatted with a rad shop in town here and they repair expansion tanks and use Red Kote.
It’s not a 5 minute fix but I should be able to save $200 or more.

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Great job on saving yourself 200.