S Type Losing Coolant... but I don't know where!

[I-Jag]

Hi everyone!

I have a 2002 Jaguar S Type with the 3.0 V6 petrol engine, which I acquired recently. The car drives brilliantly, really smooth and no overheating etc. However, I am losing coolant somewhere quite rapidly (it will go from max to min in the header tank within about 30 miles). I can't immediately see any puddles etc under the front of the car so I'm at a bit of a loss.

I can't see any signs of Oil in the coolant or coolant in the Oil, but the coolant is obviously going somewhere. I've had a good poke around the forum and I have noted down what seem to be the most common causes (header tank, bottom of radiator, water pump etc). But as I say, I can't immediately see anything.

I have a tool that pressurises coolant systems (I used it some years ago on another motor) to check for leaks, but whenever I've used it before I put it straight onto the top of a radiator. Can I used something like that tool straight onto the header tank? I can't think of any reason why I wouldn't be able to, given that the tank is designed to be pressurised anyway, but I want to make sure I'm not making things worse!

Thanks for the awesome forum!

[Russ68]

Hi John, a likely suspect is the header tank itself, they crack. Luckily they are widely available new and 2nd hand and not too hard to change. I went for a new one and it fixed the issue to my great relief 😉

[I-Jag]

Thanks for the reply Russ! I suspect you are correct. I've had a poke around with the inspection lamp and I can't see anything obvious... apart from coolant staining around the side of the header tank. I've had search around and I have seen a new tank for around £60 so I'll fit one of those and see if it makes a difference.

[I-Jag]

After more investigation, I have found the culprit... the radiator! The problem got much worse quite quickly but I was having trouble tracking where the leak was from, but eventually I managed to replicate the problem just running the Jag on the driveway. Once the engine gets up to temperature, there is a jet of coolant shooting out of the top back of the radiator just next to the header tank. The jet is spraying straight across the engine bay and hitting a spinning pulley opposite, which is then spraying the coolant everywhere, which is no doubt why I've been having such a hard time locating the fault.

Looks like I'll need a new radiator! DOH!