I was having overheating problems in my 97 XK8 Convertible with 67K miles. Found "Orange Julius" like substance in the coolant tank and when it dried it left a orangish white powder on things.


I back-flushed, flushed, and back-flushed until the water stopped bubbling and ran clear. I could put the garden hose in the passenger (US) side top of the radiator and get plenty of flow out the thermostat housing and coolant tank.

Put everything back together and it still overheated.

On a whim (nagging voice in the back of my head) I took the water pump off today. BINGO!!! A water pump without any blades is an idler pully!


I had been hearing an intermittent terrible noise that I thought was timing-chain tensioners, but it looks like it was what was left of the impeller blades scraping on he numbs of the broken blades. The odd thing is that even with a mechanics stethoscope I couldn't hear the noise in the pump. I'll post if that is fixed or I have a 3rd problem as well.

 

Excellent diagnostic work. Good luck and keep us posted....

 

AC0FC,

Well done tracking down the problem. Recently I did a R&R of the front engine cooling system.

Saw similar sludge all over the place in my system. I put it down to a previous owner mixing the red/green coolant causing gelling. Had some on my shelf and did a bench check to make sure my Liqui Moly chemical flush dissolved it.

Check out the bottom of your expansion tank as there seems to be baffle walls to catch sediment there. Mine was full of sludge too.

Did you ever ever find the broken plastic impellers as they might be blocking clear flow somewhere ?

Good of luck with replacing the water pump. Go for a new one with a metal gasket as some come with paper gaskets. There’s a debate as to whether you go for metal impellers or OEM plastic impellers. I’m in the metal camp, but it’s down to availability more than price.

 

Good call on the expansion tank. I have a garden hose with a small nipple on it and connected it to the hose on the back of the coolant tank. It ran milky orange/white for quite a while.

As for the impeller blades, there were enough pieces for 3 blades but they were all polished edges as well as what was left of the impeller. It looks like they laid in there and just bounced around till the pieces were just fragments. I back flushed to make sure anything left was pushed back rather than jammed farther in.

About the impeller blades material, I don't think the material is as important as the shape of the blades. The plastic ones are shaped with a more sweeping curve and the metal are a stamped bent tip. The complex curve of the plastic gives a better flow with fewer vortices than the harsh angle in the metal ones and therefore less prone to cavitation. The metal would probably last longer in the heat environment than the plastic, but the local store only had plastic and it's a relatively quick job to accomplish.

I would imagine a top-notch cooling system is pretty important there in Bahrain!

Over the first year of ownership I just seem to be chasing the repair demon from one place to another. It ate a set of new rear tires in 1200 miles so had to have rear-end removed, find the bent part and re-installed ($3800). Then started getting an an intermittent noise at the front of the engine. Then it overheated. Fixed to water pump and had to flush the cooling system. The next day the noise became non-intermittent and loud. Found bad serpentine belt idler pulley. Now my occasionally topping-off the power steering has turned into dumping the entire system (somewhere) in a matter of miles.

I'm just waiting for the timing chain tensioners to rear their ugly head!