Been doing some research/reading on the running temps of the diesel engines and I can't seem to find exactly the data I'm needing.

I have a 1985 300SD with the OM617 5 cylinder (CA version but shouldn't matter). There are two parts to my dilemma but I believe them to be related.



I can't get the car to operating temp unless I'm flogging it up a grade. Around town and even on the interstate it'll only get to about 50C. When I climb the 9% grade near my home, about 3 miles in length, it'll climb to 80-85 range (which I know to be the normal range).



I suspect the PO took the thermostat out but I haven't opened to verify. Replacing the thermostat is one of my 'must dos' when I buy a used car so I'm going to replace/reinstall it regardless. But what I'd like to know is, is there a reason why the thermostat would be removed in the first place? Is it common in MB Diesels to do so? I know removing them is common place when people suspect overheating, I'm wondering if there's more to the puzzle given it's a MB.



The second question, which I believe is related, is I have no heat in the car. Not sure, yet, if it's a blend door or if it's the more obvious not having temp in the engine. My google-fu in this area suggests the monovalve needs to be replaced. Thoughts?



Thank you.



PS. My dad had a 1983 OM617 back in 1983 and he told me he remembers MB removing the thermostat but can't recall the reason why. Hence my asking if I should reinstall a new one if the previous one was removed.

I can't imagine MB removing a thermostat for any reason, much less so on a CA emissions car.
Your thermostat could be sticking open, or possibly gone by the PO. Suggest that you replace with correct one, which should put you somewhere in the 80-85C range. When working, you will reach temp and stay there barring exceptional cold or heat loads.

Your heat not working could also be the heater valve is plugged not letting in flow to the core. A good test is to put the system in defrost mode and drive, if you don't feel hot air at the defrost vent, likely the heater valve.

Good luck

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

My experience is that Benz thermostats often fail by opening too early which equals a lower operating temperature. Two of the most common reasons for no heat are a bad thermostat and/or low coolant level.

A properly operating thermostat has one purpose, maintain a minimum operating temperature. The minimum temperature is needed for emissions, moisture burn off, engine efficiency and others I'm not recalling.

Change the thermostat and good luck!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Don't worry about the heat until you see the thermo temp 80 degrees, its probably way less than that with the thermostat issue. the heater valve won't pass coolant and prevents the fan from coming on until it reads 80C or close to that.
To heat it up fster place a piece of cardboard across half of the radiator (moe or less). Slip it in behind the evap fins.

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Your thermostat is stuck open. If it was removed completely, it would be overheating.

To answer your question about not having heat, you can test voltage to your monovalve with a multimeter by taking the connector off of the top. If I remember correctly, the monovalve is open by default (no voltage), letting hot coolant into heater core which allows for heating in the car. When you set the climate control to cold, the monovalve should have voltage which closes the valve and stops flow of coolant to the heater core. I made a homemade monovalve out of home depot PVC pipe, I believe it was a half inch setup, but it allowed me to have full control of my heating because I couldnt fix my climate control. Hope this helps!

Thermostats, depending on how they are designed, can fail either by overheating or under heating. When the one on my E300D failed it failed to get up to operating temperature. This sounds like what you are seeing. I would change the thermostat.

__________________
'97 E 300 D

All, thanks for the replies. I did replace the thermostat over the weekend and now it heats right up and sits at 80-85. Heat, however, is still an issue.

Drove the car to pick up my dinner last night which means climbing a 9% grade for about 4 miles. Engine got warm 85-90ish but maintained just fine (i was driving a bit spirited). No heat at all. Not even radiant heat, in fact the vent air temp was outside temperature. This was from lower, mid, and upper vents. I'm almost wondering if I have a plugged heater core or if the blend door isn't actuating at all. Thoughts?

Additional piece of information here. I don't think the actuator for the level is working either. I can push the different buttons on the HVAC system and the air doesn't seem to move from upper, mid, or lower. It's like it's stuck in the defrost and feet position.

Do the heater hoses get hot into and warm out of the heater core. Hot in and hot out is usually a plugged core. No heat into could be an air pocket. Try parking the car nose high over night with the overflow tank uncapped.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Also check to see if the auxiliary water pump is working.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Some people drill holes in the thermostat. I am OK with drilling a small hole to help vent out the air when you are refilling the cooling system but if someone drilled holes due to overheating it is time to locate the problem and fix that.

There is a picture in the thread.

http://www.peachparts.com/shopforum/diesel-discussion/299115-thermostat-holes.html

Another issue is if the temp sensor is working properly. You say that best by actually measuring what the coolant temp is with some other device.

I had a gasoline car where the coolant temp sensor got coated with a lot of thick white crud. That crud apparently insulated it partly and it did not register well making it inaccurate. Cleaning the crud off returned it too normal. Another area is corrosion or other poor contacts of the wire that goes to the coolant temp sensor.

__________________
84 300D, 82 Volvo 244Gl Diesel

If you decide to change the thermostat, find a vid or instructions on the Inernet on how to test the new thermostat before installing it.
Candy and cooking thermometers are cheap and can be used to take the temp of the water. Dump a teaspoon of salt into the water it helps calm the water down making it easier to watch the function of the thermostat.

__________________
84 300D, 82 Volvo 244Gl Diesel

As mentioned this is easy to test ~ unplug the small black connector on the top of the monovalve and go for a drive ~ all dash vents should pour out heat and lots of it .

Before you move on from the thermostat, what color was the old coolant ? .

Was there any crud / sludge / crispy stuff lining the inside of the hose(es) or thermostat housing ? .

Once you get it to dump raw heat it's time to begin looking at vacuum hoses and the push button control unit .

Taking the time to properly diagnose the issue with $ave time, money and frustration .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Finally had some time to do some of the recommendations and get answers to some of the questions.

The auxiliary pump is working.

Heater core hoses are hot/warm. I say this as one is the metal pipe and that's hot, the rubber hose out of the back of the head is warm (about as warm as the upper rad hose).

Coolant was an orangey brown color before changing the coolant. I used Zerex G05 for the replacement.

There does appear to be some brown/orange oxidation in the coolant channels. I'm hesitant to run a coolant system flush, but I will if it is suggested.

Just today I took the two heater core hoses off and attempted a flush. I do get water flowing in both directions. However, I don't think it's the correct amount. Plus the side to which I connect the hose is building pressure. I think the heater core is blocked but maybe not completely blocked?

After seeing flow, I topped up the system with water (for testing) and run up to operating temp. Still no heat from inside the car. In fact it actually felt cool. I'm wondering if I have two issues; plugged heater core and a blend door issue.

Hi there fellow San Diegan! It has indeed been cold around here hasn't it?
I was having heat issues recently as well, and discovered that if the coolant is even a little bit low, I would have no heat at all.
After topping off and burping the system a few times over a few days, suddenly had face-melting heat. Maybe something to try?