Hello diesel fans,

The heater on my 1985 300D turbo is acting strange. Heat does not come on when the engine is running. When I turn the engine off, the heat comes on. I am thinking it might be the auxiliary pump, which probably comes on when the engine is not running, to keep the cabin warm if waiting inside with the engine off. I see a lot of stuff about the monovalve...Does this problem fit the monovalve issue?
Also what's a good resource site on how to actually replace the monovalve if that's the problem. What do you guys think?

Thank You

what model are you talking about?

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oooops... Its a 1985 300D Turbo. Thanks

Could be the monovalve. When enough heat builds up in the engine compartment after running for 10-15 mins, you can stop the car and it'll blow warm for a few mins, then it's back to the outside air temp.

disconnect the a/c compressor wires and try it again...

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Hey, Andrei, this is Paul Morgan author of "bizarro heater problem" post. I changed the monovalve last night and it fixed it. Heat works great. Easy to do and inexpensive. I didn't think the monovalve was the fault but trusted the posts I read and a fax I recieved and it was right. I recommend you try it.

I have the same problem with heat building up while the car is off and then blowing through the vents the first few minutes the car turns on. So, I bought the monovalve repair kit from FastLane but I have no idea where this monovalve is. Where is it???? Thanks.

By the way, Phil at FastLane was amazing. I ordered my parts late in the afternoon yesterday and they arrived at my door today at noon. I couldn't believe it.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

Engine side of firewall; passenger side of midline (slightly)

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1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Is it a kind of squareish unit that has some kind of electrical connection on top? Thanks

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

Hey Guys,

Thanks for all the great advice.

Is changing the monovlve a pretty self explanatory job?

Also, is it accessible through the engine bay, or do any parts have to be removed before getting to it?

Thanks

Replacing the monovalve is easy - it is located in engine compartment on firewall right next to the battery. Just unhook the unit from the hoses, take out two bolts on top of unit, and pull the whole thing out.

Place unit on a clean surface, unscrew the four screws on top, and open up. Inside you will see the plunger unit. Just replace it with what is in the repair kit. Slides right in. Then put back together in reverse order. Took me 20 minutes in total. And it did the trick.