Engine 'overheats' with heating on.

[Ubernoober]

Went out in the Chim before all the snow, but when it was rather cold, to give it it's weekly run-up-to-temp leg-stretcher. As usual, I kept the heating set to cold to allow the engine to get up to temperature quicker.

So, it got up to around 68/70 by which time I was loosing the feeling in my legs so turned the heating on. Only it didn't..... get hot, I mean. A brief blast of warmish air and then ambient by the feels of it. Worse than that, the engine temp rapidly (ie visibly) went up to 95+ and the fans kicked in - and the red ice warning was on at the time.

A tad concerned at this, I put the heating back to cold - and the engine temp went back down!

So, the symptoms...... runs at normal temps with heating set to cold - 'overheats' with heating set to hot

Fluid level looks ok in the header tank and there are no leaks I can find.

Any ideas??

[miniman]

Airlock.

[slideways]

Did it happen with the fans on or off?

[SILICONE KID]

Frozen lower radiator hose !

[slideways]

did the temperature return to normal after the fans stopped and you turned the heating on cold again?
I.E did you let it cycle a couple of times?

[Ubernoober]

slideways said:

did the temperature return to normal after the fans stopped and you turned the heating on cold again?
I.E did you let it cycle a couple of times?

Yes, just to make sure it wasn't a one-off set of circumstances, I've let it cycle up and down a few times on seperate occasions and have removed the header tank cap whilst running the engine just in case an air lock was cycling around maybe but it remains the same - normal engine temps with heater set to cold, turn heater to hot > get cold air, engine temp rises quite up to 95+ and fans kick in, turn heater back to cold > engine temp drops, fans stop, temp stabilises around 72'ish

[Harrytsg]

I believe its best to bleed air out via the swirl pot.

[TJC46]

Definite air lock or not enough coolant in the system. There is various ways to refill the system but i use the hose on the top heater pipe. Its the highest point on the system.It links the top heater pipe with the inlet manifold. undo and pull the end off the heater pipe. now use a funnel or similar to fill the system thru this hose into the inlet manifold. First undo the nut on the top of the rad. also remove the blue cap on the coolant bottle. Now as you fill you push any air first out of the rad. check this and when water comes out tighten the nut on the rad. Have the heater controls to hot and keep filling. Some water should come out of the top heater pipe at the point where you removed the hose. this now shows the heater pipes and matrix are now full. Last is to keep filling and check the coolant bottle. when everything else in the cooling system is full the level will rise in the coolant bottle. When the correct level is reached, job is done.Reconnect the hose and thats that.There usually is no need to run it for a while and check, but i would reccomend you do this as well.

[spend]

I'd check the pipes & heater matrix for leaks if I was you. Sounds like your heater is full of air.

Getting the car nose high on a slope / ramps / jack may help bleeding the heater etc.

[dog man]

Could be a stuck (partially closed/not fully opening) thermostat. I'd check for leaks and if all okay, check or replace the thermostat then bleed the system. If it was working fine before then it's either sprouted a leak of the thermostat has stuck. You need the heater on hot in order to get the true coolant level and to bleed it....if it's been refilled after a coolant change with the controls on cold it may then have an airlock, however some air will bleed out on it's own...Anyways, have a see!