hey o and thanks for reading.

so it started getting cold here in Missouri. i just got back from a trip to CA and while i was gone it snowed here and dropped to 40's and 20's (night and day). i thought my car might be hard to start - its my first winter with a diesel. however it started fine and ran fine. no problems at all during the three hour trip from the KC airport. the next day i went to meet someone to rideshare to work. we took his car. no problems getting going that morning either.

When he dropped me at my car at the end of the day (in a supermarket parking lot) i started it and cranked the heat and then went inside the store. when i came out 15min later my temperature gauge was up to 110 and the cabin was still cold. i'd never seen it go this high. i was concerned about driving it, but considering that i had a little room left on the gauge and a short distance to travel i decided to take my chances.

within a half mile of leaving the store my temperature gauge dropped. rather suddenly, and simultaneously heat started pouring out of the vents. ah that moment felt good. but one other time within the next two miles to my house the temperature started climbing and the cabin air turned cold. then it would suddenly reverse to normal.

so what's going on? this just started yesterday. i drove a little today and the problem was still there, though possibly worse.

water pump? thermostat? not enough coolant in system vs water (summer mix).

any insight would help. thanks for your time and interest.

jeff

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

110 degrees tells me there is something definitely wrong with the thermostat, the fan clutch or the water pump or all of the above.
I'd check the car carefully before you overheat it again (110 is overheating if its idling) you are skating on thin ice with this kind of problem! Thankfully you have the rugged OM617 engine with its cast iron head or you would probably already be looking at $3000 + of repair work.

After you troubleshoot the cooling system then you can fix the heater. Welcome to the cursed MB heater/climate control system.
Its likely to be the small electrical pump that circulates coolant to the heater core. The CC control panel (behind the wooden overlay on the dash) is another item that fails frequently. Bad solder joints, defective relays there are several problems that occur with it. A good used unit from a donor car might be in order for troubleshooting purposes.
The heater Monovalve is another thing that tends to go bad, it usually makes the car cold while you drive if it its bad. use the search feature on monovalve to learn about that.

Good luck - you got some work to do there!

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'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!

Sounds like you have a couple issues going on here. I would guess that the fan clutch is tired which will result in your car getting to 110 at idle. If it is the fan clutch the temp will drop once the car is traveling down the road (air moving through the radiator). None of mine get to 110 d at idle.

There is somewhat of a relationship between the coolant temp and the cabin temp but it only becomes apparant when you think about it a little. The heater core in the cabin is a little radiator. Hot coolant passes through the liquid side and the cabin air blows thorugh the air side. It increases the air temp and drops the coolant temp which is indicated on the gauge.

It sounds to me like you have an issue with your climate control system. I suspect it is your monovalve. See if there is any relationship between when you are stopped versus when you are traveling down the road. The monovalve is an easy diy'er type of repair.

The next step will be to start troubleshooting the rest of the automatic climate control system. Come back after observing when you have the issue.

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Jim

i will search on Monovalve. thanks for the tip there.

today the car ran hot up to a point and then dropped in temperature suddenly - like back to normal over a 30 second interval, and i wasn't flying down the road at that point. or those points. i thought maybe it was fan related or even a water pump problem. but i'm pretty green under the hood so i wanted to get some input before i started work. thanks.

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

Define hot.

Over 100d going down the road there is most definitely a cooling system issue. I'd try changing the thermostat first.

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Jim

is the monovalve going to have anything to do with the engine temperature?

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

Double check and make sure that the engine and reservoir are full of coolant. An engine real low on coolant can have similar symptoms.

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85 300CD
83 300TD
78 240D (daughter)

No. *********

my engine doesn't even really seem to be getting too hot - i mean i let the car idle and it goes up to 100c pretty quick, cold air blaring out the vents. any other ideas? where does the temperature gauge take its reading in the system?

i am losing coolant somewhere, but i don't see it leaking out anywhere. its possible the reservoir contents blew out through the overflow on that short trip home a few days ago.

what else could it be?

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

oh - and the big fan is running like a champ. the little one didn't kick on though.

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

That's your answer. If the coolant is low, it won't get pumped though your heater core. I had this happen before on my '75 300D many years ago. I would notice that I didn't have heat anymore and my temp was up. All of a sufdden some coolant would flow and I'd have heat and the temp would suppdenly drop.

After this happened a couple of times, I got to know that whenever I started to loose heat that I was probably low on coolant. It was ALWAYS the case.

Top off your coolant and you'll be fine. (I don't think I ever found my leak)

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

coolant filled - still no heat. i found a leak - actually didn't find it yet but discovered that coolant is leaking, somewhere below the thermostat, i can see it collecting on the top of what looks like the oil pan.

with the coolant filled to the brim, i started the car and let it idle. it did not overheat as before. the coolant leaked slowly. at one point when the heat was above 80c i stepped on the accelerator for a second and the coolant temp went down.

could be the water pump?

what lies below the thermostat, attached to the engine?

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

Sounds like you could use a new water pump, if I remember correctly it seals with an O ring and not a gasket. When I bought my 240D that was about the first thing I did, replace the thermostat & water pump. I was having a lot of warm then cool periods when driving the car, no more since thermostat & waterpump replacement.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.