rtbrjason

On the E550 (2007), is there only one coolant temperature sensor? I had noticed my coolant temperature ranging from 167 to 221 degrees Fahrenheit as per the OBD2 port. The gauge on the cluster never gets much higher than 80 celsius.

I ended up doing a thermostat this week which comes with a new sensor in it. I also picked up a separate coolant temperature sensor but it appears to not be for this car. Does anyone know if the gauge has a separate sensor from the one used by the ECM?

Also, 167-221 seems like quite a large range. None of my other cars drop as low as 167 once warmed up. Is this normal for this car? Changing the thermostat and sensor made no difference.

kajtek1

I think they have 2 separate sensor, but never could confirm it.
I recorded similar difference on W210, where I displayed temperature on climatronic.
Pushing the car at 80mph on long grade with 114F outside had the cluster gauge showing 85C, while climatronic went to 96.
All was still within specifications, so I did not worry about it.

konigstiger

0009050600

rtbrjason

Thank you, this was very helpful. I can locate it by feel from the top but can't quite maneuver enough to get it unplugged or pulled free. I think I will take a try at attacking it from the bottom next time it's on a lift.

Kwijibo

The M273 uses an electronically-operated thermostat and the ECU purposely varies the coolant temperature in a range between 80 deg. C and 100 deg. C. This range is about three LEDs on the dash gauge.

The promotional literature claims that varying the coolant temperature benefits efficiency and emissions.

If you're concerned that the OBD reported temperatures are not accurate, you can verify with an infrared thermometer.

If you're concerned with the large temperature operating range, what you're seeing is probably normal.

rtbrjason

Thanks for the insight. Mine is bouncing between 75 and 105, so not that far off from what you've mentioned. The gauge on the cluster usually shows 80. At most it goes one or two bars above that, but never gets near 90, let alone over the 100 mark.

rtbrjason

I did end up doing a coolant temperature sensor. This was a bit of a pain and a little over my ability to get to so my mechanic friend ended up taking care of it for me. There was no better access from the bottom and he ended up doing it from above.

After a 60 miles or so of driving, I'm noticing the temperature is no longer dipping into the 160s. We've also had a fairly substantial change in weather. It's only been in the mid 30s here today so it could also be a function of that. Hopefully it will warm back up here and I can get some data in similar conditions to compare to.

NewShockerGuy

Thanks for the follow up. I'm going to be doing this shortly. Just wanted confirmation if one could see the temp sensor or not... doesn't seem like it's going to be as easy as the actual thermostat in the front.

-Nigel

2007_e550

Is there only one coolant Temperature sensor?

NewShockerGuy

I think I only changed the one at the back of the block. It was a PITA to do so. Nex time I wouldn't replace it if I didn't know 100% that it was bad. I figured it was cheap, and why not replace it since I am already doing other stuff... it proved to be a frustrating experience, though not impossible.

To my knowledge there was only one on our w211, 2009.

-Nigel