Thermostat

[91yearcivic]

I've changed the thermostat on my 91 Civic, bled the coolant and released as much air as I think is in the system.

It runs good, but after about a 1/2 hour or so, the car heats up again. At this point I flick the heater onto hot (with the fan off) and it corrects itself to about halfway. I've only run it for about a 1/2 hour and it seems okay, but the heater has to be on hot.

Any ideas?????

[munkaii]

When you run the car for about half an hour, does the radiator fan switch on at all? Given you have a new thermostat and its functioning properly, it should cool the coolant.

[91yearcivic]

Yeah, the fan switches on.

But flicking the air from cold to hot instantly drops the temperature to normal running temperature. Could it be the head?

[dumped echo]

Make sure the car is bled properly. If there is a bleed nut, make sure you use it to bleed the system. Also make sure the thermostat was installed the right way up, with the bleed hole on the top.
Flicking the heater on is acting like another radiator, which is allowing the coolant to cool, but obviously it isn't going to suffice in the long term.

[TODA AU]

Have radiator checked it's probably blocked...

[Bludger]

i'm having quite the opposite, fan appears to never come on, had a cracked radiator, lost half the coolant, but never overheated.fixed the crack, then now have to work out the fan