XJ6 & XJ12 Series I, II & III 1968-1992

4.2 thermostat housing - how can I stop the leaking?

Old 03-11-2019, 10:25 AM
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Default 4.2 thermostat housing - how can I stop the leaking?

Apologies if this is discussed elsewhere, but I can't seem to get the search to work correctly.

76 XJ6C with 4.2. Have only had it a short time, but it began leaking after being driven (previous drives = no leaks) and then began leaking any time motor was running. Could not pin down where, exactly, so replaced all hoses. In reattaching the thermostat housing (that complex aluminum crossover piece), it seemed impossible to keep the gasket, thermostat and housing lined up and despite my best efforts, it leaks upon filling (even before motor start up).

Does anyone have experience with solving this? Should I be using RTV on the gasket? If so, which side? Or both? Is it possible the thermostat slips out of place and the housing won't seal as the lip of the thermostat is caught?

Or if there's a vintage Jaguar shop in the Temecula, California, area anyone can recommend, as I am moving at the end of the month and the car needs to be running to transport.

Any advice appreciated.
Old 03-11-2019, 12:37 PM
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I would make sure both mating surfaces are totally flat if it leaks, shaving it the same way they do blocks and cylinder heads. Have you tried two gaskets?

I remember a Volvo 1800-ES I had with the B20 engine, the water pump gasket would leak. Someone suggested two gaskets and the problem stopped.


Last edited by Jose; 03-11-2019 at 12:52 PM.
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