Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Thermostat

Just thinking outside the box…rather than a thermostat issue, could this be a problem with the fan coming on too early?
When you took the old stat out, was it actually in the stuck open position, proving that it was faulty?
You say that with the new stat installed everything seemed normal until the fan cut in and then wouldn’t go off until you switched off the engine,
So just a thought. Dont know whether it could be a sensor issue or something to do with ecu.

Thanks for that, I wasn't certain when they became a single circuit, even so, if you switch your heater fan on when the ambient temp goes cooler at night you will still a drop in your water temperature, Same effect, as when water temp rises in stationary traffic, switch your fan heater on and the water temp falls.as you have increased your effective fan water cooling operation capacity.

What I was trying to isolate obviously not very well, was whether as it was colder at night when driving the car was he putting the heater on, which would cool the water temperature he was experiencing. I also wonder how reliable the instrument readout is and whether he has a drain on his electrical circuits at night eg all the lights on, heater on which may be influencing his instrument readouts. I know it shouldn't do, but we are talking Morgans exposed wiring and poor earthing contacts, condensation in instruments that tend to dry out when the lights are on all could be an influence , if the obvious is not the issue. etc.

Just to add to my earlier suggestion, but I still could be barking up the wrong tree!
I don't know if the 1.8 engine is similar to my 2011 2 litre. On mine, there is a temperature sensor screwed into a multi-piped “cooling flange” (not to be confused with the housing for the spring loaded stat, up front) which is awkwardly located at the rear of the cylinder head. It sits under the air filter and coil pack and as well as several large bore and small bore pipes there is a cable connector which attaches to the sensor.
I discovered this when I had to change the housing last year as it was weeping coolant.
This sends signals to the ecu to control fan and other things that may affect engine temperature like mixture etc.
If you have one of these, it may be worth first inspecting the wiring for damage and also pulling the plug to make sure of no corrosion.
The sensor itself is a replaceable part (ebay) as it is a brass body screwed into the plastic body of the “cooling flange” and may be about £10-£12.
Worth a try if all else fails?