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1999 C43 AMG, 1998 C43 AMG
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604 Posts
Discussion Starter #1
Alright, this has been going on for 2 years, but I'm only now looking into it.

As the title implies, I'm having a hard time getting the car to warm up; both the engine and the interior. Having a weak interior heat isn't all that weird. You typically just replace heater core = done.

But my engine has a hard time getting hot, too! It struggles to get above 40 degrees! If I leave it running to warm up, in about THIRTY MINUTES it will reach 80 degrees, plus the heater will be working noticably better (but not perfect). But as I begin to travel down the road, the engine and heater temp quickly falls to lukewarm.

Also, a mysterious coolant leak I can't find. It's making no puddles, but it has a slow leak somewhere making me top it off every couple weeks. Perhaps this is related...

Not burning coolant. Already fixed the head gasket. Engine runs like a champ. But I think I have the only m104 on the planet that is running TOO COLD.
 

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2013 VW Golf Sportwagen TDI, 2011 Mazda 2, 2000 E320 4Matic Wagon (retired),1994 C280 (retired)
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3,488 Posts
The very first thing that would come to mind would be a thermostat that has failed in the "open" position. I read your post twice to see if there is any mention of a thermostat having been replaced and I don't see it. I hesitate to offer this advice because I know you are an advanced DIY'er and have in all likelihood considered the thermostat. But I have delved deep into the evil that is the cooling system on the M104, and this is the only reason I can think of that a car that is otherwise working properly would fail to reach operating temperature in a few minutes.
 

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2001 CLK55 AMG, 2002 C32 AMG
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1,637 Posts
sounds like a thermostat issue to me, at least to solve the engine coolant temperature issue. maybe there is a separate issue with the heater as well, but you wont know until you get the coolant hot.

the mercedes thermostats are designed to fail open. mine did it. i say replace the thermostat and coolant and see how if it helps.
 

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Registered
1999 C43 AMG, 1998 C43 AMG
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604 Posts
Discussion Starter #4
Wow. I'm kind of embarassed.

I had no idea the thermostat fails open on these things.

Needless to say, that fixed it. Hah.

Thanks for the tips guys. I was THIS close to replacing all of the hoses on my car, as well as the heater core.
 

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ML320,C230, F250, Bayliner, Mountain Bike, Fleetwood Motorhome etc...
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1,836 Posts
Wow. I'm kind of embarassed.

I had no idea the thermostat fails open on these things.

Needless to say, that fixed it. Hah.

Thanks for the tips guys. I was THIS close to replacing all of the hoses on my car, as well as the heater core.

My thermostat stuck open and I had the same problem as you but I didn't wait 2 years to fix it... lol
 
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