[71RestoRod]

You always want the engine running at temp. A cold motor is less efficient but more concerning is the condensation that tends to build up inside the block, creating sludge, rust and generally speaking an unhealthy operating environment.

It's also true that engines can run cooler with thermostats installed. It just depends... I've seen this first hand with flathead Fords which are notorious for running hot. The water pumps circulate coolant so fast that the radiator doesn't have a chance to do it's job. We slow down the flow by installing thermostats, restrictors, etc. I've seen some guys get the best results by cutting back the impellers on the water pumps.