Hi all, I'm a brand new 1982 300D turbo owner (convert of a co worker) and love the car. It has its qirks about it but there are two i need to figure out. First is the heat - -it's pleanty hot when I have the car at idle, but when i get up to 40 or so just air, not cold, not warm (its cold out side!) just cabin temp mabye.....and never throught the 2 center vents. Second is the the car will diesel, often just for 2-3 sec, but once in a while mabye a s long as 30 sec, althought Ive never had to use the stop lever. Are the two related? or am a looking at rebuilding the monovalve and the Vacuum pum?
Thanks!

Assuming the engine is getting up to temperature (80C) you lack of heat is almost certainly due to the monovalve:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ428Y1CDDBN&year=1982&make=MB&model=300-DT-001&category=All&part=Mono+Valve+Repair+Kit

The center vents are not intended to blow heat, they should be shut off in heat mode. The car failing to stop right away is just a vacuum leak (assuming your power brakes are working, it's not a vacuum pump). Take a look at the vacuum lines under the hood first.

1. No heat at high revs, I hear that this is a mono valve repair. Order the repair kit. The repair is quite easy to do, just undo 4 screws. In the case of my 85 300d, I had to take the metal plate out and undo two screws to access the monovalve. Quite easy on the 82 300sd. Just undo the 4 screws. The rubber diaphram is usually worn out.

2. You have a vacuum leak if the engine takes a long time to shut off. Get a mityvac and start troubleshoot and repair all vacuum leaks by first replacing any warn out rubber vacuum line connectors.'

3. No center vent air. My 300d is having the same problem. It looks like the vacuum pods under the dash are not working properly because of vacuum problems or that they are just bad. Or the acc is not controlling them properly.

__________________
1987 Mercedes 300sdl, 280k mi (daily driver)
1982 Mercedes 300sd, 205k (occupying driveway)
1985 Mercedes 300d, CA, 148+ mi.
1986 Chevrolet suburban, 50k? or 150k? mi, diesel
1998 BMW 740il, 120k mi (for sale)
1999 Honda CBR900RR, 42k
1997 Jeep Wrangler Sport, 103k miles (sold)

Different issue, he said the center vents are not blowing heat, which is correct. If you are not getting vent/AC from the center, you have something wrong.

If you get no air at all from the center vents (heat or a/c) then the vacuum pod for that vent is broken. As it is the worst to replace, most folks choose to just jam the flap open, fixing the problem and also allowing the vent to deliver warm air as well as cold, which is nice in the winter.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

It's going to be cold in the morning. If you disconnect the wires from the monovalve it is likely you will get full heat until you have a chance to repair it.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

To clarify, the center vents on his 300D do not open for heat; they only open for vent/AC. If they never work (heat or AC) it's a problem.

Thanks everyone for the gret tips...It was cold today, 20F and I did disconect the monovalve (2 prong wire clip on top) - this did dive me heat no matter where I set the temp dial, but I still only get great heat @ idle and luke warm air driving speeds. shouldent the monovalve be sprung open due to the disconect? havent had time to search out the vacuum lines.....mabye this weekend..

First things first, is your engine staying at operating temperature? If the thermostat is stuck open or not installed the cold air at driving speeds will make the engine cold. Check your temp gauge and make sure it's at 80 degrees when driving. If it drops when the car is at speed you're not making heat.

Also pull out the glovebox and make sure the foam tube that connects the temp sensor is in place. Search the forum for 'foam tube' if you need more info. Once you get the glovebox out look up and the underneath of the dash and you'll see the foam tube there or two plastic tubes with a 5 inch gap between them. If it's missing connect it with a piece of 3/4" heater hose.

The vacuum leak that is causing your engine to run on may be causing problems with the vacuum elements that control the ventilation system. I personally can't keep it together in my head what the 'normal' position is for each one of those and what would happen if you lost vacuum so that they returned to the default setting.

also make sure your thermostat is working correctly. I had the same problem on my 82 SD. Testing the thermostat in a pot of water on the stove and using my temp probe showed the thermostat would open at about 180 degrees but as the water cooled it stayed open till down to around 100 degrees. This was why i couldn't maintain good heat. It never closed allowing the water to heat up. Also my temp gauge would jump up initially to 80 on the dash but the more i drove it went lower and lower. HTH Mike

sorry - i should have mentioned it but my running temp is fine, warms up to about 90 or so and dosnt change much at all.