1983 300D 144,XXX miles

Alright, I bought this one a few months ago with a coolant leak from under the water pump housing. During this time it was warm out so it wasn't that big of a deal to check the coolant level every time i took the car out, i would just top it off and go. The fan worked fine and still does, and the AC was great. When it started to get cold, I noticed the heat would work on and off, sometimes just switching to no heat with the blower still working, sometimes not coming on at all until it reached the 80 or so degrees C, and sometimes I would have to shut it off and on, push different settings, and adjust the temp wheel before it came on again. And it always hovered around 80 degrees, like it should. If the heat was working perfectly, defrost or vents, it would always shut off if i went faster than 65 mph (the heat, not the fan).

So, I took it in to my friend and mechanic, and we replaced the fan clutch, water pump, thermostat, and lower oil hose (and put on snow tires, and he only charged me $80 ). I figured that this would probably take care of the problem. After all that work, the leak is gone but the temperature hovers around 90 degrees, climbs to almost 100 degrees when going up hill and the heat is still erratic and shuts off past 65 mph. It is less erratic and it gets warmer faster but the higher temp worries me. The temp will drop down to around 80 or a little higher when the heat is working and cranked.

From what I've read and searched for so far, I think this is a monovalve issue? What's the difference between getting a new monovalve and buying the repair kit? Yes, I'm using green coolant but so much of it was pouring out of my car that I couldn't justify getting the good stuff to watch it end up on my garage floor. Will switch as soon as my problems are solved.



And, I realized that back in the summer when I bought my first Benz and came here for help, I never introduced myself. So: Got a veggie oil 1981 non-turbo 300D and drove it all summer, came here frequently to read up and learn to work on it, asked a few questions and fell in love with the car, and realized I was killing it with veggie oil. Sold it and bought the '83 turbo from a member and here I am. Now I come here a few times a day to learn as much as I can and read up. Thanks for all the help so far, and are there ever get togethers up north?

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

Seems to me you either have Air still in the coolling system or thermostat issues. How many miles have you driven it since the repairs were don
e? Hopefully just by driving it would burp all the air out. But if not you would have to try to refill the coolant through the upper radiator hose and go from there. The other issue is that your thermostat could be faulty or has a wrong temperature range. 80 bucks for the repair is very cheap, so I think he put in a generic thermostat. A good Behr unit is around 22 bucks.

As far as your heating is concerned, you might want to make sure the Auxillary pump is working. That is located near the alternator mounted on the body. Once you set the temp to heat, the it should be running. And as you mentioned, check the mono valve but I would get a new one if it is the case. The CCU could be also faulty.

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1983 123.133 California
- GreaseCar Veg System

The $80 is the friends price for the labor for this guy, but all the parts I bought myself and brought to him. I bought the thermostat that NAPA said would fit my car, was this the wrong one and why? As far as burping goes, after the repairs I drove it home, let it cool off a little, and then opened the expansion tank cap enough to let air out but not the fluid. Is that burped enough? I've already read about the "park it on an incline, fill from the upper radiator hose" fix, maybe I'll give that a shot. I've driven for about 250+ miles after the repairs, including a long drive (1 1/2 hours) to family for thanksgiving. What's a CCU and how do you check it? And how do you tell if the aux. pump is working? By looking at it? Thanks.

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)

My assumption was for parts and labor. As far as the thermostat, I would of purchased a Behr, they are usually more reliable. Not saying the Napa types are not, but on a side note it can be easily be put on backwards. I would start first with the purging the air out and then look to see if the thermostat is put on backwards. The proper placement is the spring is away from the radiator towards the engine.

The CCU is hard to trouble shoot, you might need another one to compare. The auxiliary pump, you should be able to hear it running when the heater is on. One guess is you might have a bad connection in which the higher speeds knock the wire out of place.

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1983 123.133 California
- GreaseCar Veg System

The issue of loosing heat at faster speeds is very consistent with a torn monovalve diaphragm. A repair kit will solve that problem.

To verify that your diaphragm is torn, simply remove the 4 screws at the top of the monovalve and remove the insert.