OK, not entirely scientific, but this information may help. I had to run a few loads of gravel over the weekend, up a 6% grade for around 10 miles, where load weight estimated around 8,000 to 8,500 lbs. Ambient temp was around 40 degrees and I was in tow mode. I run Penzoil full synthetic and my 2019 Ram 1500 Laramie Sport has around 13K miles on it, powered by a 5.7 HEMI.
First Load
- Ran 4,200 RPM, which resulted in 60 MPH.
- Engine oil reached 260 degrees about 6 miles up the hill and held there.
- Coolant reached 225 degrees and held there.
Second Load
- Ran at 3,600 RPM, which resulted in 50 MPH.
- Engine oil reached 260 degrees about 8 to 9 miles up the hill and held there.
- Coolant reached 225 degrees and held there.
Third Load
- Ran 3.200 RPM, which resulted in 45 MPH.
- Engine oil reached 254 degrees at the top of the hill (and was still increasing prior to cresting the hill).
- Coolant reached 225 degrees and held there.
My conclusion is that, these engines are engineered to reach an engine oil temp 260 degrees and hold there, depending on the engine load requirements. At no point did the power derate, or the speed drop off, or any warning lights appear. I thought it was interesting, though, that the analog temp gauge didn't move at all throughout any of these trips. It stayed just left of center the entire time.
By the way, I have a boat with a GM Marine 6.2L Super Charged LSA. It doesn't matter what conditions I run it in, it runs at 210 degrees coolant temp. I don't have an engine oil temp gauge so can't tell you what that runs, but I think these newer engines just run hotter than older engines.
Hope this helps.