2 weeks ago I had the low coolant light come on. I topped up the expansion tank with about 1 cup of coolant and all was good until yesterday. I checked the level and when I removed the cap it still had negative pressure even though I hadn't driven the car in a week. and I could hear the coolant gurgling into the overflow tank. I don't think I have a leak since the pressure didn't relieve itself. After a short drive it was puking coolant out of the nipple shown in the picture. (this isn't my car I got the picture from the internet) I put another cup of coolant into expansion tank and it ran fine with no leaks once again. is this just a bad cap?

 

That second outlet from the Expansion Tank is blanked off in all but the earliest cars where it was used for a second bleed hose to the top of the Radiator.

Graham

 

That nipple is supposed to be sealed. You might try a vacuum hose cap and a clamp and see if that will hold. I tried JB Weld on a tank leak and it only held for a few months. Nothing is really going to seal it from the outside.

I see a new tank in your future.

 

Agreed. Once these plastic tanks are compromised, the only decent solution is to replace them. You're not alone - we all have to do this at some point....

 

Before I replaced just one part, I would begin by performing a pressure test to determine the health of the entire cooling system. Fix it once by including all known failure points.

These cars have cooling issues at the T-Stat housing (shown), the coolant overflow tank, the tank sensor, the heating hoses behind the engine, and misc hoses like the two solid plastic lines connected to the overflow tank. Get a pressure tester on there to insure the rest of the system is up to spec. g.

 

I will order a new tank this morning, thanks guys for the quick response! Flushing the cooling system was #7 on the list of things to do. Now it's number 1. I have a feeling I won't be bored this winter once the snow falls, the list grows daily, However, I still Love this car!!

 

I just bought one a couple weeks ago. The best price I found was here (around $147 incld. shipping): Jaguar Parts by Model XK8 / XKR*-*COOLING SYSTEM If you can't find it listed, search the part number and it will come up.