91 300E Heating Problems

In the cold weather, the heater is sporadic. Once the car is warm, especially when it is raining, the only way to get it heat up the inside, is to floor the gas pedal. I'll get some mist on the windshield, and then the
hot air comes out and it gets nice and toasty.
That will last for a little while, it gets cold and then I have to do all over again.
Any ideas?
Shivering in Vancouver, Brian
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What's the engine's usual operating temperature?? It should be about 80 degrees C..
Have you checked the coolant level?
Have you felt the heater hoses to check if both are warm after driving a few miles?
It could be that the heater is, in fact working, but that a vacuum leak is causing the warm air to be constrained to the heater by a (vacuum powered) duct door.
Then there's the heater control valve a/k/a the monovalve, that may not be working correctly.
You need to look at some of these to find the problem.
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Hi, Engine operating temperature and coolant levels are fine. I'll check the hoses and the other items. Thanks,
B.

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Sorry to 'butt-in' on this thread, but I also have a problem with the (screen) heating on my 300E - it heats up ok, but I can't get anything out to the screen - consequently, it mists up. It sounds like there could be a vacuum leak, but I don't know where to look! (It blasts from the side window blowers and I get cold air from the central blower, so I know the heating is working fine - controller seems to work fine as well) do you know whereabouts of, or how to check for non-functioning duct doors? I have looked at all sorts of diagrams, but I can't find anything that gives me a view of the heater ducting! many thanks for you help andy
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I believe you have diagnosed the problem generically but I can't help you pinpoint its cause. I'd start by having a serious read of the diagrams and trace the vacuum lines first on the paper to understand function, then in the car.
Hope that no one has ever "repaired" the system for their "repair" may be the real problem!
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First, let me ask, do you get 'screen' heat when you push the defrost button ? this directs all the heat toward the windshield.
cheers, guenter

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windscreen (and the fan on maximum), I get nothing - no heat, no air at all Cheers Andy
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There's got to be a defrost (or whatever you want to call it, defogger button maybe?) button, I've got one on my '89 300E and all car's I've ever driven have one of these. In any case, assuming that's the button you pushed when you directed the heat at the windshield, then there appears to be a real malfunction of the system. Probably the vacuum hoses.
good luck

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Another possibility if the cooling system was drained since last winter - an air lock. Some cars and your model may be one - I don't know - get an air bubble in their cooling system when its drained and refilled. Experienced mechanics know which ones do and act to purge that air. Just a thought.
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I do not believe that any Canadian with self respect could complain about the "cold" in Vancouver, in october none the less?
What the hell? DId it hit 40 over night?
What are you a transplanted californian?
Sheesh, Marty
PS Sorry no help on the technical problem
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