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Hi folks,
1998 XK8. Today, quite suddenly engine temp rose and fans came on, luckily was near home so hobbled back. Quick look showed nothing leaking under the bonnet and no sign of leaking from the valley pipe. No water in the coolant reservoir, checked the expansion vessel in the wheelarch and it is clear that is where the water was coming from. No obvious pipe split, it looked as though it has just vented out via the tube that feeds to the outside at the bottom of the wheelarch. Topped up the level, took about 2 litres and went for a drive. Within 10 minutes same thing happened again. I am thinking possibly water pump failure? I changed the cooling tower and thermostat several months ago and it has been running fine until today, so I am sure they are not at fault. I propose to change the water pump and see what happens, do people agree?

Hi Andy, does sound suspiciously like a water pump issue given the symptoms and the rapidity of the outcome. Would go with your current diagnosis.

Jim M

Thanks Jim, as it is relatively easy worth a try anyway.

Ok, so removed the water pump, looks ok actually with no broken vanes on the impeller. Unfortunately one of the bolts got slightly rounded off, I think they are M6 50mm bolts, does anyone know the part number? And does anyone want a working water pump as now I have 2

As you suspect, the bolts should be M6 x 50mm flanged items, part number JFB10610B. Mike.

Thanks Mike.

New water pump fitted. I now suspect (hope) it was the cap on the reservoir, rather than the pump. Fitted a new cap and have run it until fans cut in, seems ok, next is take it for a run locally and see what happens.

Good luck with the test run. Mike.

So taken for a run and all is good. Think it was a failure of the header tank cap, so as pressure built it all flowed back into the overflow tank in the wheel arch and then out through the vent pipe.
£4 for a new cap…
Oh well, at least I have future proofed the water pump.

Commiserations! Mike.