Poor heater performance at idle

Danno · Post by **Danno** » Wed May 14, 2008 9:11 am

Hi Fellows. I'm really stumped with a problem that I've got with a Mk 3 Polo (6NZ1Y..... and AUC [1.0] engine code) and I'm really hoping you can help.

When the engine's idling the heater performance is poor - just luke-warm air, however, as soon as you rev the engine hot air is available in abundance. Road speed makes no difference. You do need good heater performance in congested old Edinburgh!

I thought that the cause might be the well-trodden path of a loose or part-disintegrated coolant pump impellor giving poor circulation at low revs. In fact the pump was fine, tho' I've changed it, obviously. The low-engine speed fault was unchanged.

Next thoughts were that the thermostat and/or thermostat housing were at fault, inhibitiing the flow of water to the heater circuit at low revs/ low circulation pressure. Again the housing & thermostat appeared fine - although with a thin, light grey, deposit - although not a heavy encrustation - of what might have been leak-stopper - on them. Replaced them both, anyway, without curing the problem.

Finally it occured to me that the heater matrix was part-blocked, perhaps by leak-stopper, only allowing adequate flow/heating when the coolant pump was above idle. Pulling off both of the hoses and blowing through them the circuit certainly didn't seem obstructed at all - nothing like the matrix in my much-lamentd MGB was, anyway. As swapping a matrix is such a labourious job, certainly not one to do speculatively, I thought of you guys(!).

Has this been seen before? Anyone any ideas?

Thanks, Dan

jonboy · Post by **jonboy** » Thu May 15, 2008 10:49 am

the heaters are just crap! your lucky it even works! its just the way they are. mine gets more powerfull the faster i go!

SpikeyG40 · Post by **SpikeyG40** » Fri May 16, 2008 4:46 pm

hello mate,

what age is your polo? from that model number i'd be thinking it is a mk4 (6N).

the age of the car will help us determine if your in the right section!

Chally_Rai · Post by **Chally_Rai** » Mon May 19, 2008 7:53 am

Hrm.... I was inclined to agree with Jonboy on this one at first but then I remembered I have used the foot well to dry soaking wet shoes while sat in a carpark before, so maybe not! Mine take frigging ages to get hot...but once about 15mins has gone by I have no problem with heat. The feet heaters are the best! The face ones aren't meant to produce heat, and the one under the windscreen are a bit lame power wise but they do get hot. I wouldn't know how to fix it though :S sorry!

I have a reverse problem...When I'm in hot summer traffic I have to blast hot air into my car to take it away from the engine and stop the thing from over heating!Not nice....

jonboy · Post by **jonboy** » Mon May 19, 2008 6:14 pm

hhhmm if its a 6n then im suprised as my old one had a s**t hot heater in it.