Quote:
Originally Posted by SD1too
Hi Bob,
I'm sorry to have to say this but I don't agree with what Michael ( mbonwick) has said here. Your coolant temperature should never drop as low as 79˚. The thermostat is designed to keep it at a minimum of about 92˚. When the car is stationary or slow moving in traffic, this should steadily increase to 104˚ when the slow speed fan should trigger.
Your temperature is varying widely depending upon engine load which is not correct. Your system is not pressurising which means that you won't have the protection of a raised boiling point. When the conditions are right you will continue to lose coolant, but it will be intermittent. Having a 1.8 you're then at risk of the incorrect diagnosis of head gasket failure. 
I had exactly your symptoms with my SD1 many years ago. The expansion tank was metal and the outlet pipe was brazed into it, except it wasn't! When I tried to remove the hose clip, the pipe wobbled. There was no coolant loss from the site, it was being ejected through the cap overflow but intermittently. Once that connection was repaired the fault was cured.
There's nothing for it Bob but a painstaking investigation I'm afraid. It's amazing what you can find when you really look! 
All the best,
Simon |
I’m not mechanical minded, and I have to leave any investigation to those who know what to look for. However I have ordered a new PRT and will get that fitted.
I cannot see any leaks with the engine running, even shining a torch into the hidden depts of engine bay.
But all your suggestions, and those of others have been taken on board.
Many thanks.