[SideValve]

Originally Posted by SD1too

Hello Peter,
Small, persistent coolant loss can be caused by flattened 'O' ring seals on the expansion tank cap. Have a look at that.

I fitted a new cap a little while back. It fixed the pressure problem I had at the time but I suspect this is different - no unusual pressurising and no sign of any loss via the cap.

Originally Posted by SD1too

Is the coolant level too high? Can you see the 'MAX' tab inside the expansion tank when you peer inside?

I only ever fill it to the correct max mark.

Originally Posted by SD1too

When you say "no airlock", could you let us know what you've done to eliminate that possibility? For example, have you drained, refilled and bled the cooling system including raising the expansion tank?

Yes, tried that. Haven't re-drained this year but if I pull the inlets off I will do it again. Have lifted the tank and filled etc a few times.

Originally Posted by SD1too

Does "no overheating" mean that your engine has passed the radiator fan "demist" test and with the instrument pack diagnostics activated the running temperature is in the low nineties when the car is moving?

I've not tried that recently, will give it a go. I have watched it on OBD reader while driving and seems fine.

Originally Posted by SD1too

Oh, and any coolant pools in the 'V'?

V is fine. There is a trace of dried pink round the base of the thermostat but its old and dry. I guess it might have leaked when a previous owner had it but no sign here for 5 years.

Originally Posted by SD1too

I cannot stress enough how important it is to check the basics and make no assumptions.

Best wishes,

Simon

Thanks for this Simon - I'll do the demist test but I think the next step is to check the inlet gaskets and perhaps peek in the rear rocker.