My 1997 XK8 with 85,000 miles has suddenly started overheating. I've replaced the thermostat and temperature sensor. I've flushed out the radiator and replaced all hoses and the antifreeze.
Shortly after starting the car, the electric fans come on and a gurgling sound comes from the coolant system. Antifreeze is flowing back into the expansion tank and filling the tank so it flows out of the overflow tube and onto the ground causing the coolant level to drop.
The only thing I can think of that I haven't checked yet is to pull the water pump off and inspect it. I have removed the serpentine belt and checked the water pump for excessive play, and there is none. It feels OK.
Does anyone have any suggestions for me? I'm running out of ideas.
Thanks

 

You should definitely change the water pump. The original design left a lot to be desired and should be replaced with an updated model with metal impellers as opposed to the plastic.

 

Sounds like alot of air in the system remaining. There is a good DIY document in the FAQ thread for this subforum that describes how to properly purge the air from the car after doing a flush and fill of the cooling system.

Is water moving through the upper radiator hose? can you feel it being pushed by the water pump?

 

And, of course, this could be caused by a Head Gasket leak.

 

That was my first thought when I read about the fluid overflowing the expansion tank. The exhaust gases are forcing their way into the coolant, causing the coolant to overflow. Then there is no coolant left and the engine overheats. I suppose it could also be caused by a blockage in the cooling system, but you've already flushed it. You can have the coolant tested for exhaust gas, but if it's happening that quickly I wonder if there is enough mixing of the fuel and exhaust gas for the test to actually pick it up. It's worth a shot, though. So if I were in your shoes, I'd get my coolant tested for exhaust gases, if that checks out OK I'd remove the pump and check the impeller (replace it if it has a plastic impeller). Then I would flush the system very very very thoroughly. Remove the hoses. Flush anyplace where there might be a blockage.

 

Check your oil. A head gasket leak may leak water into oil

 

Thank you to everyone who offered their suggestions. There were a couple of them that occurred to me, like a blockage somewhere in the system or a blown head gasket - I tried to keep THAT thought out of my mind.
Although the water pump felt fine externally - with the serpentine belt removed, it felt firm and solid, when I pulled it off to inspect it, I found the plastic impeller in pieces. Fortunately, they were all still inside of the pump housing.
So the problem is solved.
Thanks everyone. You've been a big help - especially the first guy who suggested that I replace the piece of %^& plastic water pump with an upgraded model.

 

Hey PattertiXK8,
I just wanted to check to see if your overheating problem has truly disappeared. Reason is...I had this last summer, and I had to replace the thermostat. It worked good for about 2 weeks, but then I got stuck in stop&go traffic on a hot day for about 25 minutes...and it over heated again!
It turned out for the XKRs (I think it's only for the XKRs), there's a secondary fan that turns on after the primary one. My board for the secondary fan fried so in normal driving, the primary fan kept the car cool, but once I hit stop-and-go traffic for more than 20-25 minutes, the auxilary fan was needed to cool the car. it cost me $900 for a new part...not cheap.

Anyway, just thought I'd let you know in case you run into heating problems again.

 

Thank you for your interest.
I pulled the water pump off and there were no blades left on the impeller. They had all broken off. Fortunately, they were all laying in the pump and hadn't circulated into the engine so replacing the pump was relatively easy.
Obviously that solved the problem as the pump wasn't circulating any water through the engine at all. I've never seen an impeller come apart like that before so it was the last thing I checked.