The Stovebolt Site Forums The Shop Area Engine Shop Radiator cap?

Happy Easter all,
I have a question regarding which cap to use on my truck. Truck is a 50' 3100, motor is a 55' powerglide 235. The radiator is original to the 50, in very good shape. Should I be using a 0# cap or a pressure cap as specified for the 55?
Also, what temp. stat would you recomend using? as always thanks for your input.
John

140-160 degree thermostat (180/190 degree was safely used on larger trucks)

0# cap (4# cap most likely could be safely used)

A 140 is too cold.
The engine will only run at or above the temperature that the radiator size vs. load vs. air temp permits - you can't make the engine run colder than these limits allow. If the engine runs hot with a 190, a 160 will do nothing.
The limit to cap pressure is frequently the integrity of the radiator seams, use the highest one you think is safe. Why? Because the water temperature at the exhaust valve is always above the thermostat temp, and increasing the boiling point is the only protection you have against local steam formation.

Do you plan to drive the truck in the winter when you'll need to use the heater? If so, use a 180 degree thermostat. 160 or below will not make enough heat to warm up the interior. If it's a summertime-only cruiser, use a 160 for 20 degrees more safety margin on the coolant temp. If you've got an original 1950 radiator, I'd reccomend a 4# cap max, as it's probably got one of the "honeycomb" design radiators that won't take the pressure a later type tubular radiator will handle.

Panic is right- - - -a thermostat only sets the minimum operating temperature. The size and condition of the radiator determines how much cooling gets done once the stat opens up and allows the coolant to circulate freely. A good-condition, correct size radiator should keep your coolant temperature below 200 degrees regardless of outside temperature or load on the engine, as long as the water pump and fan are operating correctly. A 4# cap will raise the boiling point 12 degrees, to 224 at sea level, less as the altitude increases.
Jerry