Fan coming on before engine hot and heater blowing cold

[Sonner34]

Few odd things happening, normally I can easily diagnosed a cooling system fault but this one has me unsure

Firstly the engine temp sensor gets up to temp very quickly normally within 2-3 mins of driving.

Secondly unless I rev the engine hard for a prolonged period of time the heater only produces cold air, even after an hour of driving.

The fan seems to be coming on very early, before the gauge says the car is hot.

Lastly every so often the car maybe 3-4 times on a one hour drive, mostly when stationary or in town the temp gauge seems to spike right up then come down almost as quickly about 30 secs later.

Car has had a new radiator a few months ago. Interesting when I checked the coolant today I noticed the coolant was low.

Defo no head gasket issue and no leaks either, I think maybe there is an airlock or the system is holding too much pressure.

First thoughts, where the normal, water pump, temp sensor, thermostat or radiator, but not radiator as new and checked for leaks, not water pump cos the water is defo still circulating but not very well.

Wh is fan coming on early?

[SteveJ]

It's an air-lock in the heater circuit - loads of advise on here of how to fix  s;-) ;-) s;-)

[carlclarke]

Does the radiator get hot? I had something like this happening where the fan would come on quickly and often but the radiator would not be hot except a little just on the nearside. Also just cold air blowing through the internal heating and what looked like loss of coolant. It took two long attempts to get the air our of the system. I thought that I cracked it the first time and then the problem returned after a few days. The second time seems to have fixed it and no problems for the past few months.