Jaguar XJS 3.6 - ? Head Gasket failure

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Sun 7 Dec 2014 18:17
Jaguar XJS 3.6 - ? Head Gasket failure - mickje

Hello All.

I have a 1991 XJ-S coupe auto. Got it 8 mths ago and run it occasionally. It had previously been laid up for just under a year, but fired up and ran fine. I have restored the interior (was very damp due to leaking screen and door seals).

I run it 2 to 3 times a month and recently it has developed a misfire on cylinder 2. On inspection the plug recess was almost full of water that I take to be coolant as the car is garaged. There is no significant coolant or oil loss, the coolant is clean and there's no sludge in the oil filler or on the dipstick.

Could this be anything else but a head gasket failure and how do I check it out? The head gasket was done 3 years and 3k miles ago by a garage I trust.
Thanks for any advice, I'm nervous this is going to get expensive!!

Mick

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Sun 7 Dec 2014 21:42
Jaguar XJS 3.6 - ? Head Gasket failure - elekie&a/c doctor

The AJ6 engine fitted to these was extremely robust and rarely gave any major problems.I am surprised it needed a head gasket unless there was some other problem to cause this.Water in the plug recess can't come from the head gasket.Either there is a leaking core plug in the head (coolant) or there is a hairline crack in the aluminium.Are you sure it is coolant in the plug hole?

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Sun 7 Dec 2014 23:05
Jaguar XJS 3.6 - ? Head Gasket failure - mickje

Thanks for the swift reply - not 100% certain it is coolant (particularly now).

I have dried it out, so will run the engine again tomorrow and see what happens. On tuesday I will be able to contact the mechanic who did the head work in 2012 so will post again after that.

Mick

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Mon 8 Dec 2014 10:07
Jaguar XJS 3.6 - ? Head Gasket failure - Andrew-T

On inspection the plug recess was almost full of water that I take to be coolant as the car is garaged. There is no significant coolant or oil loss, the coolant is clean and there's no sludge in the oil filler or on the dipstick.

Any coolant will (should) be coloured, blue or orange usually. And any fluid leaking from an engine is not usually 'clean', is it? Not much help, as I know nothing of these engines - but it does sound odd.

Can't be anything silly like leakage from screenwasher piping could it? Water in a plug recess seems likely to cause a misfire.

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Mon 8 Dec 2014 13:03
Jaguar XJS 3.6 - ? Head Gasket failure - slkfanboy

Water around the spark plugs sounds more like a leak that is causing a short and preventing the spark plug firing. As above check the colour and take it from there

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Wed 17 Dec 2014 23:40
Jaguar XJS 3.6 - ? Head Gasket failure - mickje

Thanks all for your suggestions.

Compression test showed good compression in all cylinders. So I dried it out cleaned up the plug and it ran fine. I don't know how the water got in there but it hasn't recurred. Car is now MOT'd and has done about 80 miles since without any problems.

Happy Christmas to everyone

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If you cover no more than 100 miles per day and have easy access to a charging point at home or work, then an EV is ideal for you.

Is an electric car right for me?