Parts wear with a cold engine. Don't just take the thermostat out. Replace with a 180° if you think 190° is too warm. Engine will take a long time to warm up and still never reach full operating temp without a tstat. Looks like the 2 choices for a new one are 180 and 190. So it sounds like it's correct. Can you see on the gauge when the stat opens and closes? Temp will probably go just over 190, then drop to 175 or so. Then start to rise back up to 190ish. As for the wear. Piston will warm up and expand from combustion heat. If the block doesn't get warm the cylinder won't expand so the piston rings are a tighter fit and wear the walls of the cylinder. Same thing with bearing journals. Designed to warm up and expand to create a clearance. Doesn't warm up without a tstat, any moving part wears more than a warmed up engine. It might be only a very slight amount, but it does. Stretch that out over 10 or so and it equals 20 years of wear. Not saying people don't do it, just not me or anyone with any engine building experience. Also won't have full combustion so less power.
