MG T-ABC

Does anybody know how full to fill the radiator?

Since it's an open system, I just fill it up, run the car and continue topping off as the level in the upper tank drops. The air bubbles seem to eventually work their way out. Sometimes squeezing the lower hose for a short time helps to speed the process, but obviously do NOT do this while the engine is running! You know, metal fan and all...

If I fill the radiator to the top when cold as it heats up it naturally expands and overflows. I just thought there might be some level below the top that is recommended to avoid overflow when hot.

I misread your first post a little bit. The radiator will find its own level. Once it overflows the first time, that's your level. Filling it further will only result in overflowing again.

Fill to about an inch below the top, when it gets hot it will overflow out the drain tube to it's own level. About the same method as the petrol tank......

Excellent, thank you very much. Learn something new everyday!