Ok so when I was out with the wife tonight looked down at the gauges and she was reading about 220 or so then it would drop to about 180 then back up again.but once I was going at 45 or over she'd run about 180 and hold there. Before it seemed to hold at about 175. Is it the thermostat or something else?

What is the year and series Mercedes you are asking about? I see the w115 in your username but we don't want to assume.

Could be the stat. Have you emptied the coolant recently? If so could have air bubble in system.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Sorry it's a 76 300d w115

Haven't emptied it but did start to undo the line that goes next to the airconditioner pump and it did leak some.was trying to get to the alternator easier. Could that be the issue? How would I go about fixing this?

Remove radiator cap, insert coolant. I recommend 5050 antifreeze and water. Run car until the thermostat opens, then check to see if the coolant level has dropped. In that car you want it to never be low enough to expose the top of the core so there is room for it to expand without burping coolant on the ground.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Ok will do and thank you guys for your help.

Filled it to the top ran it for a while and it held at 175.

Now check coolant level in radiator to see if it has burped any air.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well got to find out that the water pump is the issue took it by a local mechanic that was helping me with my A/C and noticed coolant on the floor. So we tracked it down and my water pump is leaking my radiator fan is also very sloppy. So how hard is it to replace or rebuild the water pump.

I forget if that obnoxious AC bracket is in the way on yours... but om61x water pumps are real easy.


...if none of your bolts are wasted.

fan clutch... also very easy... annoying. but easy.


might want to look into alternative replacement options for the very expensive clutch.

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Yeah, that one will have the frankenstein ac bracket....sorry.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Thanks for the info I will look for them and get ordering.

Fan clutch could still be good. Wobbly fan could be a loose shaft in the water pump. Had that happen a few years back on a trip in the 220D. I had installed a fan and clutch from a W123 on that engine. Got to a pal's in Tulsa and discovered the fan had a lot of wobble, and saw that it was the entire shaft coming out of the pump. Amazingly the pump was not leaking. Got a pump from a local shop, installed, and drove on.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D

No concerns. I have boiled over cast-iron head engines many times. The heads don't warp like newer aluminum heads. It probably wasn't as hot as indicated. I have seen 120 C temperatures when there was air in the system after a coolant change, which probably was just hot vapor against the temp sensor.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans