C200K 2007 Coolant Sensor Issue

[johnwild007]

This issue has me pulling my hair out .
The temperature gauge starts at cold ,slowly goes to about 60 ,then falls to 40 and
stays there, moving slightly up and down .Obviously,replaced the coolant temperature sensor. But no change.
Expert advice needed. Thermostat ,waterpump ? Please help . Trying to avoid
expensive dealerships

[CraigB]

i'm not familiar with your car but just a thought - one of those cheap temp guns pointed around the region of the sender and see if there is any change. Probably not if it is moving rapidly. If it was an old fashioned gauge, it would be a fault in the gauge itself or something that could be cleaned - couldn't say for something so much later than my cars. But at least the gun would give you confidence that its not doing damage.

[johnwild007]

Thanks for your reply.
The main issue is: Can I forget about it ? So the gauge does not show the correct
temperature,but are other readings controlled by the sensor ? like the cooling fan
or other equipment?

[John Green]

My guess is the thermostat is jammed open. This will be why it doesn't warm up. On later models this will put the check engine lamp on as the ECU realises the engien should have warmed up within a certain length or time and driving.

Either way I would start with a thermostat and coolant change.

[CraigB]

I would go with John's advice - but did you get what I was talking about? These guns you point at an object and it tells you what temperature the object is. -ie. if your concern is if the car really is getting hotter and colder and is your dash gauge telling you what is happening or has its own fault, one of those guns is your short cut to tell you what temp it actually is and if it is going up and down the same as your gauge is. If you last question meant should I be worried if my real temp is going up and down like that, then yes, that tells me something is not right and needs fixing. I'm not always clear how I describe things but I do my best!