Odd heating problem
Discussion
At idle or crawling in traffic the heater in my car occasionally seems quite weak, but full on once over 10/15 mph. It's not quite so bad if the heated rear screen, lights and radio are switched off. Of course the heated rear screen is only used for the first few minutes of a journey. On a longer journey it usually sorts itself out. Other times it's absolutely fine. Could this be a knackered battery somehow? Car is a 1990 Mercedes 190e.
If the temperature is fine and but the flow is lower, could be an alternator? Once engine speed is up a bit it's back to normal but weak at idle?
If the flow is fine but the temp drops, might be low coolant. I found that my Mazda 6 had low coolant (despite the overflow tank showing it was fine..) and would only have full temperature when up to speed. Not ideal on cold days in traffic!
If the flow is fine but the temp drops, might be low coolant. I found that my Mazda 6 had low coolant (despite the overflow tank showing it was fine..) and would only have full temperature when up to speed. Not ideal on cold days in traffic!
RazerSauber said:
If the temperature is fine and but the flow is lower, could be an alternator? Once engine speed is up a bit it's back to normal but weak at idle?
If the flow is fine but the temp drops, might be low coolant. I found that my Mazda 6 had low coolant (despite the overflow tank showing it was fine..) and would only have full temperature when up to speed. Not ideal on cold days in traffic!
Agree on the second point!If the flow is fine but the temp drops, might be low coolant. I found that my Mazda 6 had low coolant (despite the overflow tank showing it was fine..) and would only have full temperature when up to speed. Not ideal on cold days in traffic!
Check the rad when it's cold - might find it half empty but the overflow tank still full.
Could be a partially blocked heater matrix? Does the coolant system have an in/out of the bulkhead to/from the matrix?
If you have a large drop across them when warm then you may not be flowing great, but with extra revs/pressure it will a bit and provide adequate heating.
If you do have an in/out you can disconnect and flush/reverse flush (be gentle and try mild detergents first - rather than drain cleaner etc) carefully with a hose pipe (again start at low pressure).
If you have a large drop across them when warm then you may not be flowing great, but with extra revs/pressure it will a bit and provide adequate heating.
If you do have an in/out you can disconnect and flush/reverse flush (be gentle and try mild detergents first - rather than drain cleaner etc) carefully with a hose pipe (again start at low pressure).
Or as others have said, low coolant, the heater matrix is generally one of the highest points in the coolant system so might suffer first.
Possibly helpful link........hopefully your matrix won't actually perforate :-)
https://www.pelicanparts.com/techarticles/Mercedes...
Possibly helpful link........hopefully your matrix won't actually perforate :-)
https://www.pelicanparts.com/techarticles/Mercedes...
Edited by Scootersp on Wednesday 11th December 11:14
The OP comment about how it works better with other electrical items turned off suggests an electrical problem, either a failing fan motor or alternator. That the problem goes away above 15mph suggests that ram effect is able to push air through the matrix and out of the vents. The car is 29 years old. Start by checking the alternator: it’s easier to get at!
Maybe worn brushes or bearings on the blower motor? Or the fan blocked with crap so the motors having to draw lots of current spin.
worth checking things out before it's too late, one of my friends almost lost her car (early 90's Passat) to fire when the wiring to the blower motor started to smoke as the motor was drawing too much current.
worth checking things out before it's too late, one of my friends almost lost her car (early 90's Passat) to fire when the wiring to the blower motor started to smoke as the motor was drawing too much current.
I suggest putting the blower on full power and see if that cures the symptoms.
In lower speed settings the blower fan motor is powered through a big resistor which is usually cooled by the air flow through the fan. It's quite common for these to overheat and damage connectors/wiring, leading to intermittent and reduced fan performance, eventually leading to total failure.
If the symptoms go away when the fan is on full speed that shows that the rest of the cooling system, heater matrix etc are OK and it is just a fan effectiveness issue.
In lower speed settings the blower fan motor is powered through a big resistor which is usually cooled by the air flow through the fan. It's quite common for these to overheat and damage connectors/wiring, leading to intermittent and reduced fan performance, eventually leading to total failure.
If the symptoms go away when the fan is on full speed that shows that the rest of the cooling system, heater matrix etc are OK and it is just a fan effectiveness issue.
Thanks all, just to clarify the blower fans are blowing as strong as ever, but at idle and crawling traffic the heat is much reduced, but the air output at max settings is unaffected.
When I took the car out at lunch, turning the fans off then on again at full blast seemed to make it produce more heat.
When I took the car out at lunch, turning the fans off then on again at full blast seemed to make it produce more heat.
Edited by sparks_190e on Wednesday 11th December 15:47
GreenV8S said:
You seem to be saying that the air volume flow rate is OK but the air comes out cool, but gets hotter (briefly) if you turn the fan off for a while.
That suggests you don't have enough coolant flow through the heater matrix. Perhaps it's blocked.
Perhaps it is, but then sometimes it works absolutely fine.That suggests you don't have enough coolant flow through the heater matrix. Perhaps it's blocked.
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