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2016 metris, i live up in northern ohio, found out that my metris has no heat at idle, i can start up in morming and let it idle for an hour and it will not warm up. temp will sit at 40 degrees C.
Once i start down the road it will warm up to 85 degrees C. but if i get stuck in traffic, i can watch the temp drop back down to 40, anybody else notice this. dealer has no clue
 

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I don't know why they don't have a clue. That sounds like a classic bad thermostat to me. That is, the engine keeps getting cold coolant even when it doesn't need it. (It's better than the opposite problem which can also happen with a bad thermostat).
 

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I had the exact same problem. It happened once, when it was 5f and a load of ice on the windshield. After an hour in traffic, the van was kinda warm at best. The dealer was unable to find the problem. I haven't experienced the issue since that one time.
 

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When a dealer has no idea of of something like this, it tells me that the techs aren't troubleshooting or they are spending little time on it. Its no like they are working on a space shuttle or a nuclear drive submarine.
 

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Actually, I think I figured out what it is. Next person that has this problem consider the following:

There's a shroud, so I am not positive, but Mercedes has traditionally used a three fan cooling design- a large fan driven by the engine (either the crank shaft or more likely the serpentine belt) and a pair of thermostatically controlled electrically driven auxiliary fans.

Something in these cars is convincing them that they are much hotter than they are, causing the coolant valve AND the auxiliary fans to run in cool down mode. The car, driving at high use, where this kind of cooling normally occurs, will eventually reach operating temperature. However, under any other circumstance it will cool down below operating temperature.

If this is not so, your car will, at idle, sound like a vaguely dieselish gas engine with rail chatter. If it is so, you will also here a high-speed electric whine from the cooling fans, as you would on a hot summer day with the A/C on. Anyone beat this out?
 
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