Strange Heater Issue

November 22, 2015

Hi all,

I posted here a while ago and had some excellent advice regarding my heater. The mechanic replaced my thermostat and reversed the inlet / outlets for the heater and things got a bit better.

Slowly, though, the heater has returned to being cold, luke warm at best - unless I'm going up a hill! Then the heater seems to be absolutely fine for a little while after until gradually returning to luke warm.

Has anyone any ideas what might be behind this?

I'm planning on flushing out the matrix, as per the long thread on here involving Mr Muscle.

Also, the car is using water...not sure where though there is no sign of water in the oil or oil in the water. Seems to be about a pint a month.

Any advice would be greatly appreciated!

November 22, 2015

If you have a mechanic then he should be able to pressure test the cooling system to system to locate the leak; loosing just 20cc a day is not easy to spot by eye ; it can be from so many places, leaking hose, radiator, radiator cap, pump, heater, head gasket etc etc

November 23, 2015

Hi oldcodger.

Thanks for the reply - I've got that on my to do list.

Ay thoughts on why the heating works only when I go uphill?

November 23, 2015

Ay thoughts on why the heating works only when I go uphill?

Probably because the engine has to work harded to go uphill.

What about you temp gauge needle, how long does it take to get up to the normal position ( typically halfway up)?

( assumes you are not coasting down a long hill for miles just after you start up )

Once the engine is fully warmed up, it should not drop below its normal mark, unless you are really blasting out hot air from the heater at full speed for a long time..

Again these are things your mechanic should know and be automatically be checking out for you.

November 23, 2015

Hi oldcodger,

Mine is a Corolla Verso, so no temp gauge - just a blue light when cold and a red when overheating. Blue light goes out after a mile or so, so assuming all is well there.

This hill thing is very odd....even on long runs where the engine has been working reasonably hard there's still little heat. But uphill - its as if the hot coolant can somehow reach the matrix only when at an angle. Very odd. Water pump?

November 23, 2015

I would get a sniff test done on the head gasket. I have seen similar results on other models where the head was cracked and overheating going uphill. At least it is a cheap test and can be done quickly for peace of mind