Thermostat assembly ??
Thread Starter
Newbie
Joined: Nov 2014
Posts: 8
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2010 C300 Luxury
Thermostat assembly ??
I have some questions regarding the thermostat assembly on a 2010 C300. This is a car I don’t drive very often, short trips a couple times a week, and has 65K miles on it.
Several weeks ago the check engine light came on, so I stopped at Auto Zone and their scanner showed a problem with the thermostat assembly. After a couple weeks the light went off. A month later it came on again. Couple weeks later it went off again. Now it’s back on. So here are the questions:
1. If there really is a problem with the thermostat, why doesn’t the check engine light just stay on?
2. Can I just replace the thermostat, like I used to do with older cars, or does the whole assembly have to be replaced?
3. As long as the engine temp stays the same as it’s always been, does anything need to be repaired at all?
Several weeks ago the check engine light came on, so I stopped at Auto Zone and their scanner showed a problem with the thermostat assembly. After a couple weeks the light went off. A month later it came on again. Couple weeks later it went off again. Now it’s back on. So here are the questions:
1. If there really is a problem with the thermostat, why doesn’t the check engine light just stay on?
2. Can I just replace the thermostat, like I used to do with older cars, or does the whole assembly have to be replaced?
3. As long as the engine temp stays the same as it’s always been, does anything need to be repaired at all?
Junior Member
Joined: Jan 2019
Posts: 61
Likes: 11
From: Melbourne, FL
2011 C300 Sport
The ECU will throw a code if the engine does not get up to operating temperature within a specific time (like 10-15 minutes). If you drive less time than this or if the engine does achieve operating temperature it will clear the code after (I think) 5 successful operating cycles. In any case it can clear itself if the conditions are met and seem intermittent. The key indicator is the temperature does not get up to normal range. On mine it is around 90C. When this occurred it was less than 80C.
When I had this issue I swapped the thermostat. It is the whole housing, not just the t-stat.. So of course it costs way more. But, it is pretty easy to do.. You will need some coolant to re-fill the amount needing to be removed to swap it out.
When I had this issue I swapped the thermostat. It is the whole housing, not just the t-stat.. So of course it costs way more. But, it is pretty easy to do.. You will need some coolant to re-fill the amount needing to be removed to swap it out.
Super Member
Joined: Mar 2011
Posts: 803
Likes: 37
From: Bay Area, CA
2011 C300 Sport, P1, MM, Wood, Heated FS, DIY rearview camera.
I replaced mine less than a year ago, the whole assembly bought from Rockauto.
I don't remember what warning light or code I had, but noticed it took much longer time than usual for the temperature needle to reach the normal point, meaning the thermostat was stuck open.
It was easy to replace it. However, when I put the belt back, I didn't align it carefully. After a short drive I heard weird noise and found one side of belt was being rubbed off a bit. Replaced with a new belt also from Rockauto and well aligned and problem ever since.
I don't remember what warning light or code I had, but noticed it took much longer time than usual for the temperature needle to reach the normal point, meaning the thermostat was stuck open.
It was easy to replace it. However, when I put the belt back, I didn't align it carefully. After a short drive I heard weird noise and found one side of belt was being rubbed off a bit. Replaced with a new belt also from Rockauto and well aligned and problem ever since.
