VCCA Home Forums TECHNICAL - GENERAL Commercial Vehicles rad cap technology

I have two commercial vehicles with 216 c.i. engines, and alternate driving them to not allow one to think I favor the other.

In the current heat wave, the '39 tends to run hot, according to the gauge (180 - 212) while the '46 stays between 160 - 180 regardless of outside temp. Of course the 70 - 80 yr old gauges may not be precise.

I was today advised to drill holes into both rad caps so that if the water gets hot enough to boil, they can breathe, and won't cause the rads to blow

Comment?

That is pretty much normal. The 1937-1940 engines tended to run hotter. The 1941 had many cooling improvements and if the system is clean should not run hot under most conditions.
Either coolog system is "breathing" through the over flowtube. Neither radiator is designed to use a pressure cap and the 1939 radiator is venteed thru the top of the top tank so a pressure cap is not going to work.

My 1939, which had a new GM radiator and block would run at 200 Deg. in 95 Deg. temps. It never boiled over but at times would push out water under extreme conditions. An overflow tank took care of that problem.

I don't understand the drilling the hole suggestion.

WOW, a knowledgeable response within a 1/2 hour. Bless you.

Guess I am a little late to the party. Unless the overflow tube is plugged or blocked it will either vent excess vapor or liquid or both. Causing the radiator to blow is extremely remote. Holes in the radiator cap will direct coolant to places not intended.

Am from the "if it ain't broke, don't fix it" school and so am leaving well enough alone. Thx to both of you for your input

To add a comment, "hot" is a relative term.

At sea level water will boil at 212 degrees. Any increase in altitude will affect the boiling point by reducing it. I have forgotten how much the BP is reduced per thousand in altitude.

Anyway, the engine in our unpressurized old cars will take much more heat without damage than 212 degrees. The problem is in keeping the coolant in when it boils. The overflow devices will work to some extent but may be limited to capacity owing mainly to overfilling the radiator when cool/cold. Heated water expands, as you know.

Best and first thing one to consider is to limit the top tank of the radiator to about no more than half a tank level. I believe Gene has mentioned an inch or so above the flues.

As long as there is coolant in the engine it will not get so hot as to cause any damage. When the water level gets below the water pump impeller then is when the coolant may rapidly cook off and leave your engine with a too hot condition. Head and pistons, etc, suffer then. Pouring in cool/cold coolant may crack the head or block or blow the head gasket. (Best to let the engine cool down and pour coolant in while the engine is idling.) Combustion pressure will then force coolant out at a strong rate depending on how much pressure is forced in the combustion chamber.

Don't sweat a "hot" engine as long as you know the radiator has sufficient coolant and you make a mental note to check the coolant level often and especially after i has run with a temperature needle pegged. Less so, I suppose, if you have an overflow tank.

Okay, you may open fire now.

Charlie