Poor heater performance at idle
Posted: 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
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
