Oil temperature

First thing I would check is the sensor and then the dash board gauge.

 

What engine and Year? Might be oil cooler is Plugged.

 

I agree, if there's an ECM hook up and see if there's fault codes at that temp there should be. The only engine generally have 2 temp sensors 1 for ECM 1 for gauge. Sensor for gauge could be bad if ECM shows no problem.

 

I'll admit Detroit is not my field but Troubleshooting 101 is the same across all platforms. First thing first rule out the simple things I.E sensors. I'm still not convinced that there is a "Physical" (meaning actual problem) because if oil temp reached 300F bells, whistles, and the voice of God should have all been going off in your cab as well as a FC. Some sort of FC should have logged around the 250F mark. The only reason gauges exist is because people generally Americans are always on a Need To Know Basis. In the auto industry you rarely even see temp gauges. Either buy a cheap temp gauge from NAPA and find a port on the oil rifle to plug in to, or buy a cheap scanner that'll allow you to monitor temps that the ECM see's before jumping in the "this has got to be the end of the world" issue. I'd be willing to bet there is 2 temp sensors, 1 for ECM and 1 for dash gauge.

 

As a blanket rule, at 250F or above you are cooking the oil and the component itself. This goes for everything. Engine, trans, diffs, hydraulics, etc. Hopefully its just a failed sensor or wire. If the oil is really hitting 300F and you haven't bought the truck yet, run away very fast. More problems will be on the horizon.

 

my freightliner has two sensors 1 to gauge 1 to ecm no way the ecm is going to let it run at 300 very long

 

i would say failed sensor or wire as well, get a lazer thermo and shoot it at the oil filters and the pan and see what you get for comparison.