I can tell if an engine has been run without a thermostat when I tear it down for a rebuild. There will be a shiny spot less than an inch wide on all the piston skirts- - - - -the rest of the piston will be covered with varnish where it has not been in contact with the cylinder walls. Those pistons are either worn out, or badly in need of skirt knurling to get the diameter back to normal.
Piston skirts are egg-shaped, with the widest point at right angles to the wrist pins. As they heat up to normal temp they get round because there's a couple of "anti-expansion" struts cast into the piston. That only happens at normal operating termperature.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!