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Freightliner m2 with cat c7 engine low temperature showing


Active Expediter
Hey guys,

Right up front thanks for all your help

I have a 2005 freightliner m2 with caterpillar engine
As I'm driving today after fueling I noticed that my temperature gauge seemed to be showing lower than normal temperature
I'm usually between 165 and 185 when driving but now it dips even slightly below 150 and won't hit more than 165ish.
It does seem to somewhat respond and rise a bit when uphill and vice versa.
I tried looking online but wasn't able to find much more than that it might be thermostat( I guess there are 2 of them) or coolant temperature sensor???
I'm just wondering if I should be extremely concerned about this or is it something not to be freaking out about?

Once again thank you for all your input


Veteran Expediter
Thermostat stuck open? Bad sensor? I'd certainly get it checked. That engine is way too expensive to have bad info coming out.


Veteran Expediter
Using a multi meter you can test the temp sensor. You will have to find out what the voltage range is. It sounds basic but, are you running the correct coolant and is it mixed right? Extended life coolant the red juice,

Check your coolant level, and mix ratio with a hydrometer. Too heavy on the coolant might cause a false low or high temp. A chemistry test will also help the test strips tell you if you need SCA. You can pick up test strips at a Detroit Allison dealership for arround ten bucks for a dozen Im sure you can get them at a Cat dealership. Just remember the test strips are often for the OEM formula but for a quick look it works.

Im leaning twords posably a T stat.
Good luck on it
Bob Wolf


Senior Moderator
Staff member
Fleet Owner
A constantly running fan would be suspect. A check on the ECM will tell you if that is the problem. Outside of that, it could be a thermostat, sensor, or just a bad radiator cap that isn't letting it pressurize correctly.


Active Expediter
Thank you for all the responses. I checked around the truck and everything seems normal. I'm on the road right now so can't really do much more.
This seemed to have happened right after I fueled. Don't know if that matters but the truck seems to be running a bit rough as if one if the injectors was kicking in and out at times. I might be just dreaming out and feeling things that are not there but I figured its worth mentioning. Also I noticed this while running the AC. The truck seems to have normal power and all too.