Odd heater behaviour
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Odd heater behaviour
AE86 standard heater without air conditioning. Idling heater is ok, fan blowing hot/warm air. Driving, the heater suddenly goes cold after an indeterminate time and stays cold. Any ideas what this might be?
Re: Odd heater behaviour
Only logical explanation is that there is no longer any hot water reaching the heater core.
The outlet from the heater connects to the suction side of the water pump so unlikely
as it may be, perhaps you have a hose that gets soft enough when hot to collapse and
block the flow ?
Other option is some problem with the heater tap. As you can see the direction of flow
thru the tap is such that it will hold the valve closed. Maybe if the cable has a lot of slack,
or the return spring is broken or the valve can somehow vibrate into the closed position,
you could lose the heater flow. So make sure the valve does actually open wide and stay
open, assuming you have the standard mechanical heater tap of course
Cheers... jondee86
The outlet from the heater connects to the suction side of the water pump so unlikely
as it may be, perhaps you have a hose that gets soft enough when hot to collapse and
block the flow ?
Other option is some problem with the heater tap. As you can see the direction of flow
thru the tap is such that it will hold the valve closed. Maybe if the cable has a lot of slack,
or the return spring is broken or the valve can somehow vibrate into the closed position,
you could lose the heater flow. So make sure the valve does actually open wide and stay
open, assuming you have the standard mechanical heater tap of course
Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.
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- Club4AG Pro
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Re: Odd heater behaviour
Hi Jondee, thanks and all of those things are very plausible and I will check them carefully. Indeed, both of the large diameter radiator hoses are soft, I wonder if that could be it?
Re: Odd heater behaviour
I was meaning the heater hoses. A collapsed radiator hose would not make the
heater run cold... more likely just the opposite.
Some basic checks would be if you stop the car (but keep the engine running) after
the heater starts blowing cold, does it return to blowing hot air without you touching
or changing anything ?
If the engine is up to temperature and idling (heater hoses hot) and you rev the engine,
do you see either of the heater hoses change shape or flatten out ?
Cheers... jondee86
heater run cold... more likely just the opposite.
Some basic checks would be if you stop the car (but keep the engine running) after
the heater starts blowing cold, does it return to blowing hot air without you touching
or changing anything ?
If the engine is up to temperature and idling (heater hoses hot) and you rev the engine,
do you see either of the heater hoses change shape or flatten out ?
Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.
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- Club4AG Pro
- Posts: 653
- Joined: Tue Mar 26, 2013 5:21 am
- Location: Oxford U.K
Re: Odd heater behaviour
Feed and return heater hoses are hot at idle and the heater is working. Weather is a bit crap so I'll need to wait until I can take it out to test them when the heater goes cold. Thanks
Re: Odd heater behaviour
IIRC, I could give the heater a quick feel while driving, but you're RHD. Just a one time confirm the heater's venting is open & what's blowing is what's happening in the core.
The heater's outlet goes right to the thermostat and cools it down, slowing the flow. That's as much as I'm able to guess.
HATED that Mickey Mouse design inlet side thermostat with a little disk to restrict flow when open, though the big pipe from the rear seemed like a good idea to keep 4 from overheating.
Cardboard for the radiator & rag on the oil cooler stopped my head from hurting.
Good luck.
/////
Also soft hoses when hot? It ain't warm or bad cap.
The heater's outlet goes right to the thermostat and cools it down, slowing the flow. That's as much as I'm able to guess.
HATED that Mickey Mouse design inlet side thermostat with a little disk to restrict flow when open, though the big pipe from the rear seemed like a good idea to keep 4 from overheating.
Cardboard for the radiator & rag on the oil cooler stopped my head from hurting.
Good luck.
/////
Also soft hoses when hot? It ain't warm or bad cap.
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Re: Odd heater behaviour
Thanks for the input guys, I have still yet to get out and test it further. I will report back asap.
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Re: Odd heater behaviour
So an update... finally managed to get the car out for a run and it looks like the heater core is blocked. Inlet hose is hot but the return hose is stone cold. I really hope that it can be flushed out. Any recommendations for which way to flush it, i.e with the flow or against the flow? Thanks for any help.
Re: Odd heater behaviour
Just checking... but you have checked that when the cabin control is set to full heat
the heater tap is also wide open (spindle fully up) ? If the core was clogged I wouldn't
expect the heater to work fine for a while and then suddenly stop working.
None the less, I would suggest reverse flushing in the first instance.
Cheers... jondee86
the heater tap is also wide open (spindle fully up) ? If the core was clogged I wouldn't
expect the heater to work fine for a while and then suddenly stop working.
None the less, I would suggest reverse flushing in the first instance.
Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.
-
- Club4AG Pro
- Posts: 653
- Joined: Tue Mar 26, 2013 5:21 am
- Location: Oxford U.K
Re: Odd heater behaviour
I will double check that Jondee. The actual hose from the tap was hot as l remember it.