Closed or Open Cooling System?

[mclairmo]

I am about to add a coolant recovery tank (billet cylinder type) and it appears to be a closed system tank. The coolant flows from the radiator into the recovery tank from a nipple at the bottom of the recovery tank and thus (I assume), that when a vacuum forms in the radiator, it will suck coolant from the recovery tank back into the radiator. My cap has two seals on it. My question is what is the advantage of a closed system? Will it help my engine run cooler at all? Also, what is the advantage of a higher rated radiator cap? I have several on hand (even a Griffin 24 lb racing cap) and wondering if higher pressure is better for cooling? I know that the higher caps increase system pressure which increases boiling point but will this help me run cooler or just prevent earlier boil over?

[cdowns]

a recovery system wont help to cool better//i'm not a fan of higher pressure caps on old vehicles as they just increase the chance of cores blowing out from the higher pressure that they werent designed to contain. i stick with 7-9lbs

[Hottrucks]

for each lb of presure it raises the boiling point of your coolant ( I forget what the # is I think 2* per lb) I'm a big fan of the 6 lb caps open or closed no big diff once it finds it's level it will stay there perviding you don't have any leaks..also there are a few additives like water wetter or sub zero that work very well in all my rods which have always had heat issues due to small engine compartments, big ponies and hot headers other than that use a good coolant and you won't stress your radiatior or heater core

[Stocker]

Can't recall the specs, but mine has a 16# cap which I think is correct (or maybe it should be 15#; someone will chime in). At any rate that's what I've used for 32+ years with no issues. Higher pressure will simply allow a higher boiling point, it won't make the engine run cooler.

A closed system will help cooling a bit though, simply because it will contain the maximum amount of coolant, where an open system will typically be more or less a couple inches low on coolant.

You're right about how a closed system works, with coolant dumping into the tank instead of on the ground, and then being sucked back into the radiator as it cools.

[WorkinLonghorn]

I agree somewhat. Actually,with the stock 13 psi (15psi with AC,heavy duty cooling or big block) there is also cooling taking place as coolant boils when it touches the hottest areas during heavy use. The steam produced may condense later in the system or it may be forced out the overflow,but the point is that at the hottest points it is able to boil and absorb the "latent heat of evaporation" from this action.
If you run a higher pressure then the coolant will not boil as easily at these contact points where it is hottest. The whole system could actually run too hot if no boiling was taking place.
That's my take on it anyway.

[Camper Power]

the overflow tank won't really help with cooling cause an open system is low when the engine is cold, but once its warmed up the system is (or should be) full. but also alot of race tracks dont allow vehicals with open systems on their track. as for the pressure im running around 15-16lbs, and my engines running right where i want it. also the higher pressure you go, the higher risk of blowing hoses and gaskets

[danleaman]

FYI for each pound of pressure the boiling point increases by 3 degrees.

[dwcsr]

Originally Posted by mclairmo

I am about to add a coolant recovery tank (billet cylinder type) and it appears to be a closed system tank. The coolant flows from the radiator into the recovery tank from a nipple at the bottom of the recovery tank and thus (I assume), that when a vacuum forms in the radiator, it will suck coolant from the recovery tank back into the radiator. My cap has two seals on it. My question is what is the advantage of a closed system? Will it help my engine run cooler at all? Also, what is the advantage of a higher rated radiator cap? I have several on hand (even a Griffin 24 lb racing cap) and wondering if higher pressure is better for cooling? I know that the higher caps increase system pressure which increases boiling point but will this help me run cooler or just prevent earlier boil over?

They haven't used an open cooling system since the Model T. All modern cooling systems are closed.
Yes a closed system does cool better by allowing the pressure to raise the boiling point of coolant. The use of a recovery tank helps keep the radiator full at all times and thereby helping the system cool better. Granted is not a huge difference but it helps by keeping the pressure steady in the system so you don't have a air pocket to compress before it gets to operating pressure. With any amount of air in the system the saturated water will try to release the heat into the trapped air in the system and can start a boil over. The higher the pressure in the radiator the more heat saturation the water will take to a point. The balance is getting enough heat saturation into the water without bursting the system and having a way to release the heat effectively.
The recovery tank operates as a catch can when the system is under pressure it pushes some coolant out. When the system cools it returns to the system under vacuum keeping the radiator full at all times.
For the sake of argument this is a boiling point of plain water
At sea level (14.7 psi) water boils at 212F
At 17 psi it boils at 219
At 19 psi it boils at 225
At 20 psi it boils at 228
Your 24 lb cap will boil at 238 but you may burst a tank, leak a head gasket or pop a hose, maybe not depending on the condition of your system

The point of raising the pressure is to raise the saturation point; once it boils it will not soak up any more heat and starts to release what it has absorbed as steam.

If you don't have a way of dissipating the increased heat from the water then raising the pressure doesn’t help much. Boil over is from the water being saturated beyond the capacity of your system to release the heat through the radiator. So in short you can have a 1000 hp motor with a 15 lb cap and be fine but boil over with a stock 350 and a 24 lb cap if you can't get the heat out of the water