2005 Super Duty, 6.0, egr delete, 65 mph on flat highway, unladen, coolant temp 178*, oil temp 196*. I have read that with a delete that the temp spread isn't as critical. But I've never seen this much spread before. Am I looking at oil cooler? Thermostat? Getting ready for an RV trip next month! Thanks in advance guys.

 

Change the thermostat

 

^^^^^^^^^^^^^^^^^^^^^

This engine is a lot happier around 190* and up, and will likely be reflected in your MPG and performance. You are just wasting fuel at those temps.

I will say I have not read that deleted the 15* spread is not an issue, you are still running an OEM cooler and not air cooled but perhaps there is another view point on that.

 

Ok, thanks guys. For the record, after holding at 178* coolant temp for 20 minutes or so, she finally rose to about 190*. The oil temp rose simultaneously and maintained an 18* spread. I'll change the thermostat. Seems to be sticky. Thanks again!