That was quite concerning.  Being an all-alloy engine, the Jaguar V12 does not respond well to being overheated.   When I brought the car to the workshop, it was quite apparent that it was coming from the water pump.  The Jaguar V12 holds a lot of coolant (~20 litres), but its still better not to loose it like that.

It looked like the seal had failed and after shutting down the car, without circulation, the coolant was being ejected through the water pump seal.

When I first got the car, the water pump was one of the items replaced, so I was a bit puzzled why it could fail like it did.  On the other hand I was pleased it wasn’t a more serious problem like a head gasket.

Doing some more research, it looks like it is due to water pump availability.   For the Series 1 XJ12, most of the parts manufacturers list a rebuilt pump or a repair kit.   So this is what my car got.  Unfortunately the rebuilt pump didn’t last long.  Apparently you can get new aftermarket pumps for later cars, I presume for the HE.   From what I can tell, these normally had a double row pully, but you can order a single row, which is what my car has.

Based on all that, we put on a new aftermarket pump.   My mechanic tells me that he rarely needs to replace them, so the new one should last a lot longer.   To do the job, a fair amount of stuff needs to come off the engine, but the job can be done with the radiator in situ.

At the same time they replaced one of the tensioners with a second hand unit as the bearing in the pully was a bit noisy.   The electric fan was also rubbing the shroud so they adjusted the bracket.

The result is no more pools of coolant underneath the car when I drive it.   The engine runs pretty cool.   I verified this with an infrared thermometer.

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