1948 Plymouth P-15

[Eddie M]

A 180 degree thermostat should be installed in the coolant system.  Many  uneducated people in the distant past used to run without a thermostat thinking the engine would run cooler in the long run.  Myth.
As others have pointed out, there are many benefits to the engine internally to letting the engine get to running temperature sooner.

[plym_46]

Plus running the coolant through the heater adds about 20 to 30 % more heat exchange area to the cooling equation.  On really cold weather, it might be possible to see a situatio where the stat stays closed or partially opened and the heater does most of the cooling the engine.

[bigaadams]

one should run the thermostat..the purposes are many..it allows quicker warm up of the engine thus cutting emissions and saving you fuel as a cold engine requires more fuel...as for the argument of regulating flow...while a radiator is an water to air heat exchanger, the real practice for the regulated water flow is to ensure saturation of engine heat to the water for exchange through the radiator...it is a proven fact that as the engines running at lower temps are more prone to sludge buildup within..amplify this greatly if you car is used in relatively short terms of operation..say just around the flock or loading unloading etc etc..it will take approx 30 minutes of operation to really be effective to begin removing moisture from the interior of your block.. your engine by default should run a 180 thermostat...there is a thermostat of approx 195 that is for use in extremely cold climates..those in these adverse climates often just block a portion of their radiator to make up for the temps if the hotter thermostat is not installed.

[plym_46]

I ran mine for a season with out the stat.  I don't believe it caused any harm.  If anything in hot weather it may cause the temp to run coolant to get hotter, as the thremostat works to regulate the speed of the flow.  Passing the coolant through the radiator too quickly does not allow heat to exchange properly as it is not exposed to the flow of air long enough.

The themostat does not determine the temperature of the coolant but rather the temp when the fluid starts to flow through the radiator.

I would run it the way you have it unless or until a overheat problem presents itself.

[TodFitch]

The 180 thermostat will not make the engine run hotter in summer. At least it won't if the cooling system is in serviceable shape and it is not defective. What it does is get the temperature up to where the engine is happiest quickly. Too low a temperature will cause acid and sludge build up in the crankcase which you don't want.

If you are really worried about temperature, then put in a 160 degree thermostat. Not as good for engine life as the 180 but at least it will get the engine warm enough to start vaporizing the condensation in the crankcase.

[patsy13]

I moved from a cold climate to a warmer climate and wanted to change out my 180 degree thermostat.
Can I run the P-15 without any thermostat at all??  Will this harm the engine in any way??