It's a bad idea to run any engine without a thermostat. Lack of a thermostat promotes increased oil dilution by raw fuel during the warm-up period that can cause an increased bore wear and overall drop in lubricant performance. No properly functioning thermostat will add to, or cause, overheating problems. Such problems are always due to other causes. If a thermostat fails, it almost invariably does so in the open (safe) position. In more than 40 years in the auto maintenance/repair business I can think of only one instance when a thermostat stuck closed and caused overheating. Running an engine below its optimum operating temperature is always a bad idea. If the vehicle overheats in stop-and-go traffic on hot days, fix the problem; don't paper over it by removing the thermostat.

Does anyone run a thermostat in their four cylinder car? My PA doesn't have one, and the owner's manual does not show one, but a spare head I have has one in it, and apparently, the parts catalog shows one. Any thoughts?