07 5.9 coolant temp running low

[JaredCole]

My truck has always run between 190-200 degrees but lately while pulling my 8k trailer the gauge dropped to maybe 160. I checked the thermostat and it failed so I replaced it. But now it is still running colder and wont get above the same temp. Cant figure it out. I have the head studded, the truck has never overheated and no white smoke out the exhaust. I have the fleece coolant bypass, could that thermostat have stuck?

 

[Michaelsloft]

My truck has always run between 190-200 degrees but lately while pulling my 8k trailer the gauge dropped to maybe 160. I checked the thermostat and it failed so I replaced it. But now it is still running colder and wont get above the same temp. Cant figure it out. I have the head studded, the truck has never overheated and no white smoke out the exhaust. I have the fleece coolant bypass, could that thermostat have stuck?

Did you replace the radiator cap?

 

[sag2]

Are you using a genuine Mopar/Cummins thermostat?

 

[JaredCole]

Did you replace the radiator cap?

Yes

 

[JaredCole]

Are you using a genuine Mopar/Cummins thermostat?

Yea that's probably why, I've read these engines dont like non OEM t stats

 

[Missouri Mule]

Is your fan running to much ? That would cause cooler temp readings.

 

[Missouri Mule]

Left you fuel for thought. 1rst and 2nd gens used a mechanical fan clutch. Which could start freezing up or rotate pulling no air.
3rd gens used a electronic controlled fan clutch. With no time to research this I will take a wild assumption that on the 3 rd gens and Later models ????when the clutch was going or the electronics was starting to have problems the fan would continue to rotate ( as in pulling air) SO the driver... and truck.... would not be disabled out in middle of no Where!

 

[sag2]

Yea that's probably why, I've read these engines dont like non OEM t stats

Actually the OEM is the only one I would run.
As for the fan operation, if the thermostat is working properly a fan stuck "full on" should never drop the coolant temp.