I had a 502 with B&M 250 on top of it. All the good stuff so on what not. At last rebuild, I only ran it for 100 hours or so with the blower on top then removed it. It is now basically a HP500 clone. This engine has lived 200 hours with a 120 T-stat. I am wondering if a 140 T-stat might be a better choice.
Is there any concern with switching from the 120 to 140 this far into the service life? Perhaps the piston/rings and walls were sort of married and broken in at a temp and shape corresponding to that temp and switching up to 140 may upset that. Probably overthinking this but I don't want to compromise a good engine. Same builder has done the last rebuilt and it runs perfectly as well as the previous blower motor. When the engine builder bored it last he set and clearanced everything to run cool and for the blower motor at the 5psi boost.

I thought the 502's had 140° ?? At least a 90s engines did

Don't fix what's not broke. Apparently the engine builder did not have an issue with the 120°F stat. And that's what counts. My opinion... not so much. lol

The 120 stat was selected not because it was optimum for an NA engine but for a blower motor. The cooling requirements are different and would be a compromise for one versus the other. The crux of the question is having an engine that was broken in at 120 degrees and the corresponding block and piston relationship be change much when operating at 140 degrees? I am aware that the 90 502 came with a 140. Merc probably wanted that for a reason and my builder wanted 120 for a reason. The reason for 120 was unbolted and sold.