Jag X350 untraceable coolant leak

[Risonax]

The initial message was deleted from this topic on 10 November 2023 at 23:29

[Semmelweiss]

Thermostat housing. It's plastic and gets brittle with age. First thing I did when I got my X350 XJ8. Slow but persistent coolant loss.

[Getragdogleg]

Borescope down the pistons and see which one is cleanest. That's where the head gasket is weeping or which liner has gone porus.

[stevemcs]

Anything wet inside the footwell ?

[reddiesel]

I suspect the expansion tank , more often than not as soon as the tank gets warm they weep at the seams

[996Keef]

Get a UV dye and torch kit

Put the dye in and run it , then go looking with your magic torch.

It's going somewhere, if you can't find it with the torch , then it's drinking it

[Semmelweiss]

reddiesel said:

I suspect the expansion tank , more often than not as soon as the tank gets warm they weep at the seams

Good shout. The union at the overflow easily snaps, and the float switch eventually doesn't float! Easy DIY replacement in about 30 minutes. The complete tank available from Berkshire Jag components for about £26.

[McGee_22]

996Keef said:

Get a UV dye and torch kit

Put the dye in and run it , then go looking with your magic torch.

It's going somewhere, if you can't find it with the torch , then it's drinking it

This. Works every time and shows the smallest leaks.

[V12 Migaloo]

McGee_22 said:

996Keef said:

Get a UV dye and torch kit

Put the dye in and run it , then go looking with your magic torch.

It's going somewhere, if you can't find it with the torch , then it's drinking it

This. Works every time and shows the smallest leaks.

What a great tip!!

[Patrick Bateman]

Is the heater matrix a possibility?

My Clio used to use lose coolant and it was the matrix that needed replacing. No visible leaks but there was a smell of coolant.

Have they pressure tested the system and kept it under pressure for an extended period of time?

[alabbasi]

If it's not leaking externally, it's leaking internally. Time for a leak down test.

[kev b]

Nothing to lose so you could try using superglue and bicarbonate of soda to seal the leak.

Probably not a permanent repair but I’ve used this method on broken plastic parts many times.

[Semmelweiss]

Risonax said:

The issue is the a dignosed cracked plastic thermostat house. The bigger issue is Jaguar have discontinued the part, with no replacement. No UK stock.

Guess the car is now parts only. Shame.

Anyone know of sources for complete thermostat housing, non-supercharged V8 X350.

Berkshire Jaguar Components?

[Semmelweiss]

kev b said:

Nothing to lose so you could try using superglue and bicarbonate of soda to seal the leak.

Probably not a permanent repair but I’ve used this method on broken plastic parts many times.

The Thermostat housings become brittle with age, and are cheap enough to replace. If you are going to drain the coolant, jack the car high up enough, removing it, degreasing it, and making a temporary repair is probably not worth the effort.

[P700DEE]

Same thermostat fitting for standard and Supercharged so upgrade to an Aluminium one! That's probably the reason the plastic ones arn't made any more. Might even be the same as the XK8/R

[Semmelweiss]

You can flush the heater core matrix before buying anything. It's probably gunged up. It's a common fault, usual symptoms are driver's side heating doesn't work, or cooler than passenger side.

[alabbasi]

Do it the old way. Jack the car up in the front using axle stands as high as you can go so the nose is higher than the heater core. The the system with the heater turned on and the fan running full blast

[McGee_22]

There are tips and tricks to refilling and building most coolant systems - for my E39 V8 it is have the front of the car higher (a slope or kerb will do) but also to fill it not through the header tank but through the (disconnected) top radiator hose.

[kev b]

Try using a vacuum coolant bleeder, they are straight forward to use the only drawback is you need an air compressor.

I used one with great success on a Porsche Cayman which has a pretty convoluted cooling system, saving me a lot of faffing about with the bonus of knowing there were no surprise airlocks to show up later.

When you vacuum the system down you can leave it for half an hour to check for leaks too.

[GeniusOfLove]

kev b said:

Try using a vacuum coolant bleeder, they are straight forward to use the only drawback is you need an air compressor.

I used one with great success on a Porsche Cayman which has a pretty convoluted cooling system, saving me a lot of faffing about with the bonus of knowing there were no surprise airlocks to show up later.

When you vacuum the system down you can leave it for half an hour to check for leaks too.

Just used one of these for the first time to fill an X150 XKR 5.0 which requires you to remove the coolant bottle and hold it in the air to try and fill it manually, and always gets airlocks. It was absolutely superb, sucked all the hoses flat, kept the vacuum for a while to make sure the system was sealed properly, then it filled the system from a bucket in about 45-60 seconds. No airlocks at all!