Hello everyone, im brand new to the jaguar community so forgive me if this topic has already been discussed. My 1999 XK8 has been giving me overheating issues. It would run for about 20 minutes, than it would start overheating and pour almost all of its coolant out of the expansion tank in the wheel arch. I recently upgraded the thermostat housing to the metal one, and fixed all the leaks coming from that area, there is a slight leak in one of the hoses under the coolant reservoir, right above the transmission, between the engine and firewall. I'm going to tackle that and possibly a new coolant reservoir cap for possible over pressure. Is there anything else I should look for/missing? Common causes that I should tackle first? Thank you.

 

The connections on the coolant reservoir are likely crossed/incorrectly routed.

 

does this not look right? Its a late 99 model. Thank you

 

Did the overheating start after you replaced the thermostat housing?

 

im not sure, i bought it last week with this overheating issue with the plan to restore it, i could see the housing gushing out coolant and assumed it was the issue.

 

In that case, I'd buy an inexpensive kit to check for exhaust gases in the coolant. Search Amazon for "exhaust gas in coolant tester." Your symptoms are also those of a bad head gasket.

 

Hmmm, if thats what your leaning towards, do these photos help your theory? When i did the first flush the coolant looked very odd. But the oil was perfect.

 

That does look correct!!!(never mind)

 

Yes, that coolant looks really fishy. Kind of oily too. You could just have a bad water pump, but with an engine of unknown provenance, it's best to cover all the bases.

 

Someone might have put some kind of "Stop Leak" in the coolant. Water pump is long overdue if it's never been changed.

 

Ok, I'll replace the waterpump as well. Would you guys know what hose i have down there that is leaking? Its right under the throttle body.

 

true, I don’t see any obvious sign of coolant on your dipstick, but the oil looks to be quite used up, judging by the color alone.


not a perfect way to evaluate oil I know, as many quality lubricants will darken after numerous heat cycles. But nevertheless, it does appear like an oil change is in order. Or at least a used oil analysis (UOA). Reputable labs, like Blackstone, can provide a UOA at a very reasonable price. Especially given the information provided.

I don’t have one done at every oil change, but at least every 10,000 miles or yearly, whichever comes first. I consider the UOA to be an early warning signal that can alert an owner to trouble before it has a chance to become expensive.

Z

PS: aside from measuring metals in the oil, a UOA can measure how much of your oil’s additive package is remaining, and hard at work. An additive package that is less than 50% of the value of the new oil isn’t enough to be reasonably effective. You provide the lab with information like what brand of oil, what viscosity, and whether any oil was added post oil change. So the lab can use those values to determine what percentage of the oils additive package is remaining.

 

Yes i was planning on doing an oil change and track down the oil leak the car seems to have after the car can run for more than 20 minutes. Shes definitely a fixer upper but we'll get there

 

Depends on what's meant by "under." There are two coolant hoses that connect to the back of the throttle body and those can certainly leak. The "octopus" hose also runs behind the throttle body, although it doesn't tend to leak in that exact spot. There are several heater hoses that are under the expansion tank, as well as the hose connecting the tank itself. I'm going to go out on a limb and say that none of these have ever been replaced and it's long past time to do them.

 

it connects to the bottom of the coolant reservoir, there's a little hose that comes from the throttle body that connects into it at like a intersection and then the hose appears to go towards the engine

 

That little hose connects to a T fitting, with the other ends going to the octopus hose and one of the valley hoses. That T thing probably needs replacing, too.

On mine, when I got it, I just pulled of the entire intake and throttle body, then replaced every stinking hose on the engine. It was a PITA but I no longer have to worry about coolant leaks for another 20 years. Which is one of the few things about this car that I don't have to worry about.

 

so I've just run this test, which was not easy because after it got to temperature, the coolant would overflow out of the reservoir like 30 seconds after turning the car on so I had to pump for 20 seconds then run to shut the car off before it overflows, wait a few minutes and do it again like 4 times until I was happy with the amount of pumps I did. Even with this ridiculous overflowing, the fluid stayed blue. So very confused at the moment

 

if it is coming out of the atmospheric recovery tank (in the wheel well), it sounds like the cap on the expansion tank is defective PN MJA4440BA

 

This cap alone could really be the cause of such sudden overheating?

 

You mentioned the above in your first post. So, the expansion tank cap maintains system pressure when operating but also has an internal valve that redirects excess coolant to the atmospheric recovery tank (wheel well) when hot and then draws it back into the expansion tank as the engine cools. If the valve has failed, it could continuously send coolant to the atmospheric recovery tank. Replacement cap is anywhere from $10-$25 so it's a cheap test. The other test you can do is a pressure test (Harbor Freight or borrow a pressure tester from Advance Auto, just know the loaner kits don't always have the proper fitting for our expansion tanks)