Does anyone have any ideas on why my XK8 is over heating. I replaced the thermostat and the water pump still looks new. (1 year old). The radiator seems clear when running water through it. The water in the reservoir does not seem to go down much. It only took 3 qts after draining the radiator.
It runs for about 10 minutes and the fans come on then after another 5 minutes, the engine temp quickly rises to hot.

 

Replace the pressure cap on the fill tank (around 20 bucks)...it may have bad or missing seals. The system must pressurize or it will overheat.

If that does not do it, remove the thermostat and see what happens. If it does not overheat then new thermostat is bad (not unheard of) or it was installed backwards.

It is best to monitor the temperature with an OBDII reader. Letting the gauge repeatedly hit the hot mark is putting a lot of stress of thermal stress on the engine and could damage it.

 

+1 on WhiteXKR. After mine overheated and replacing the head gaskets, I monitor the temp with a obdii scanner. Removing the thermostat is a good idea, but check for any codes as well.

 

Why isn't this likely to be air lock, guys?

 

Don't run it without a thermostat or it will overheat badly. The thermostat in a 97 xk8 works in two ways simultaneously. The thermostat valve opens to allow flow through the radiator but also the large disk on the rear of it closes the bypass duct in the housing. If you just remove it, the bypass and radiator flow are both open and coolant just mixes and does not flow around the system properly.

Check the temperature of the top and bottom rad hoses with an infrared gun and see if it really is overheating. You may have the wrong temp sensor installed which will make the temp gauge read too high. You should see about 195f when normal, 205f when getting too hot with the gun.

Also if its getting too hot the fans should run faster.

 

Welcome to the forum Dick King,

When you get a minute, please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some info about yourself and your vehicle for all members to see.

In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

 

Dick, what have you done so far?

Do you smell coolant at any time, or do you have any coolant below the car? Have you performed a pressure test? Could you define "the engine temp quickly rises to hot." Is this based on the temp gauge, or other means?

On my car the "low" fan kicks in at 205F. I have not waited to see when the "high" kicks in. How much water/coolant do you lose?

Also, do a search on the XK8/XKR section of the forum. There is loads of info on coolant issues.

 

Thanks Guys,
I put a new cap on the reservoir and it did stop the bottom hose from collapsing, but it is still overheating. It takes about 10 minutes for it to come up to temperature and the fans kick on. After about 2 minutes the needle rises to red very rapidly, so I shut it down. I am also not getting any hot air from the vents. I am afraid to drive it, so I can't get it to a shop to check codes.

 

I really think you have an air lock. With the engine cold, squeeze and release the upper hose repeatedly. Then check the coolant level. This happened on a friends XK8 and the symptoms were exactly as you reported.

 

First, pull the radiator top panel to be sure there is not a lot of debris between the condenser and the radiator. Mine had a lot in there, enough to restrict airflow. I had to blow it out with a hose.
I agree, the symptom is an airlock. Be sure the thermostat is the correct one from Jaguar. It should say "waxstat" on it. Be sure the wiggler valve is in the 12:00 position, if it is not, it may airlock as the wiggler valve releases air trapped behind the thermostat.
The thermostat must have the metal disk on the back of it to close the bypass when it opens or the system will always overheat as the hot coolant does not go through the radiator fast enough with the thermostat open. If this does not fix it, dump the coolant, then slolwy refill until the tank is up to full, then start the engine with the cap off and wait until you have a coolant level drop when the thermostat opens. Shut it off, let it cool and top the tank off. Try it again.

 

I wanted to mention that the problem of debris between the condenser and radiator is very common. I talked to my Jag indie and he said he had an 08 XK still in warranty come in with overheating. The Dealer had replaced the water pump and it did not fix it. It had so much junk in there it took awhile to remove it all. That was the problem.
My 06 with 43,000 miles had the same pile of junk in there, it was amazing how it all got in there!

 

I say the water is not moving and I would be checking the water pump.

 

Have you measured the actual temperature at the hoses yet? It could still be a bad sensor causing the gauge to read high.

 

If you're still struggling P.M. me - I'm in Fort Myers- I could drive over and check the temperatures for you with my laptop OBD program.

 

Thanks Everyone,


The problem seems to be fixed. I noticed there was liquid from the overflow tank on the floor after I ran it last evening. I refilled the reservoir again this morning and drove it for about 30 minutes. It did not overheat. Yah!!
I think it was a combination of air being trapped in the system and the radiator cap was bad. I am also getting heat from the heater now which I was not getting before.
Thanks Gus and everyone else for all of your help and ideas.
Dick King

 

Dick, I honestly hope your overheating issue is resolved, but I would still try to get the actual coolant temperature. The temperature gauge is not a good indication of the real coolant temp. The gauge is pretty useless, as you will see from many posts on the forum.

Get the RealGuage from WhiteXKR (#2 above) or something else to get the real temp. Mine overheated without me knowing and the gauge never moved above the middle. Years back my old 5 series BMW had a comment in the owners manual at the section about the fuel gauge. "Having faith is good, checking is better!" Very wise words!