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2017 GLE350 2014 C250
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Discussion Starter #1
2014 C250, 81,xxx miles. Symptoms: Warm / hot weather: gets to operating temperature quickly and stays there consistently even on 90+ degree days. Cold weather: takes a long time to warmup (+-10miles), even longer around town with heat on from start. Turn off heat, temperature begins to climb back up, turn on heater, temperature drops quickly and will not go back up for a long period of time with heater on, or until highway driving. Temp sensor at thermostat is fine and no codes with scanner. Ive read some other threads on here with similar issues, some say normal, some say thermostat. Car runs great. Anyone had the same issue and any luck with resolution (or not). Thank you
 

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Your thermostat is stuck open, it needs to constantly open and close to keep temp at the safe operating range , its not good to drive a cold engine, change it as soon as possible.

If working properly it will inhibit the flow of coolant allowing the car to effectively heat and then close once the coolant temperature lowers, and it will continue to do this thousands of times while you drive around to keep the car at a safe operating temperature.
 

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Discussion Starter #3
PRK - Thanks. The engine does get up to operating temperature, and stays there when highway driving... do you think the thermostat is still sticking open?
 

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If it goes cold when you use the heater, yes change it, as the heater core is just another small radiator with a fan on it and the temp should not fluctuate a great deal, it should hover around the same temperature no matter what you have on or not.

Your first post indicates a thermostat failure, the fluctuation from cold to operating temp then back to cold if you use the heater indicates its stuck open and not doing its job.

Not good to drive a engine if its not at operating temp as it causes premature wear because the tolerances are less when cold.
 

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If it goes cold when you use the heater, yes change it, as the heater core is just another small radiator with a fan on it and the temp should not fluctuate a great deal, it should hover around the same temperature no matter what you have on or not.

Your first post indicates a thermostat failure, the fluctuation from cold to operating temp then back to cold if you use the heater indicates its stuck open and not doing its job.

Not good to drive a engine if its not at operating temp as it causes premature wear because the tolerances are less when cold.
 

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2017 GLE350 2014 C250
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Discussion Starter #7
For those of you that are interested, I did the repair... Some notes:

a. Dont let anyone tell you that it is an easy job on the EVO engine. It is as painful as changing a water pump.
b. You MUST remove the PS line from reservoir to pump (at the pump end is fine). You will never get the job completed without doing so.
c. Be very careful with electrical connectors.. they WILL be brittle.
d. Get yourself an 8mm ratcheting wrench. Some of those bolts near the top of the housing are impossible to get at with the correct socket.

Im not sure what they were thinking designing something that should be a simple 30 minute fix instead of a three hour major job.

What was wrong with mine? Have a look at the picture I have included, you can plainly see that the rubber seat gasket is torn. The thermostat was opening and closing correctly, but the torn gasket was allowing coolant to pass though all of the time. Hope this helps. J
E2B11C3D-CA8C-4230-8654-89E8E25E68E0.jpg
 
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