Hi all, I think I have some sort of cooling issue with a second hand B20b motor I've put in my 73 145. The reading on the temperature gauge that I am used to as normal is 9 o'clock and the original B20a motor I had in the car would stay there with very little fluctuation if indeed any at all. This B20b engine however will only stay at 9 o'clock if the heater valve is open, that's just the valve open without the heater fan actually going. If the valve is closed then it runs a little above 9 o'clock when travelling and rises more fairly quickly when at junctions or in traffic. With the valve open it will sit and tick over stationary without hardly moving at all. Like I said, the old B20a motor did not really change at all regardless of whether the heater valve was open or closed.

- It acts exactly the same with two different thermostats fitted so the thermostat appears to fine
- I've fitted a new radiator as the old one was quite bunged up with crud of some description
- The water pump looked fine as I replaced the gaskets and seals before putting the engine in
- Hoses appear to be fine
- Coolant system burped and the level does not really alter from hot to cold
- Little copper pipe under thermostat disc is present, not blocked and at the correct height
- Thermostat is the correct sort with the disc at the bottom

Running out of things to try so any help appreciated.

Thanks

Tony