W-Lewis,
You are absolutely correct on
oil temp based on old hand knowledge and what I see on my Backdraft and C7 Corvette.
Oil temperature is about the same and may go 5 to 10 degrees over water temp after a long time.
The Backdraft I have purchased used has an
oil thermostat but much bigger than the Earl one posted and had a price tag of about $300. $110 for this one made by a big name manufacturer might be nice.
Not knowing where you live but I do know that oil coolers are good in Texas during the summer as additional oil cooling is nice for all those 95 plus degree days. All extra cooling is good in the South.
An old oil and gas engineer that worked for CoreLab for 30 plus years where all he did was test oil told me oil temps should be higher to burn moisture and other impurities out of the crankcase. 140 degrees is nothing.
Best,
Nathan