I ran the 10-40 4T Mob. oil once....Where I live it gets fairly cold in winter and dang hot in summer
I noticed that in hot weather the engine made more noise than with the 20-50.
One day about 2 yrs ago I was in one of my rare moods. It was dead of summer...apx 100*F + day and for about 2 hrs I was flogging the hell out of the Ol'Girl.
I pulled into a large boat ramp at the lake and slowly cruised around when my oil light came on..I stopped in the shade shut it off an checked the oil level....The oil was so thin...it was like water....I could barely see the oil on the dip stick
Well being me I stuck my finger down into the tank and...it did not take long to check the oil level.......and Yes it was full.. DO NOT Check Hot Oil with Finger!!!!
I will not run 10-40 oil again....
So next time I get in my mood and run the Ol'Girl hard again...I think I will grab each header to check if the tempatures are the same on all 3 headers..
I have never been known as the sharpest marble in the bag...