Coolant system question

Blu Dice

Blu Dice

Senior Member
Someone explain the need of a pressurized coolant system vs having a non pressurized system. And when and why did Ford go to a pressured coolant system. Is it practical to change from a non pressured system to a presurized system, and visa versa? What can go wrong if you switch from a pressured system to a non pressured system?
 
The higher the temperature you can run an engine at the more efficient it is. Modern engines run at much higher temperatures and that requires a pressurized system. Early Ford can also benefit from a higher operation temperature but there are other issues that come into play, such as the under hood temperature. The overall under hood temp and engine temperature lead to other problems such as vapor lock and/or boiling the fuel out of the fuel bowls. As with about everything it is a compromise, you want the engine temperatures as high as possible without leading to other issues. With modern engines the use of fuel injection and recirculating fuel supply, computer control, etc, the temperatures can run much higher.
 
Because once it boils, you better shut the thing off . . . as the coolant can no longer do it's job.

I also think there is a secondary reason: Having a sealed system also keeps the coolant in the system - or in the overflow tank (modern cars). On my 32, you can't fill the system anywhere near the top - it will overflow a lot of water out the drain tube . . . and obviously it doesn't magically come back.

Also, I agree with JSeery - just didn't want to get into the other reasons for higher temperatures (by design).
 
The 32 to 53 Fords don't need to be pressurized but need the over flow
tube sealed off with a low pressure "safety valve". With an open overflow
tube with higher water temperatures or higher RPM's of the water pumps
water is pushed out the over flow tube. Most of these cars have a 22 quart
system and cooling depends on the amount of water or coolant the size of
the radiator, fan, the amount of coolant in the system and the gallons per
minute flowing through the system. The increase or decrease of any of
these effect the end result which is the operating temperature of the water
the engine. We are not interested in raising the boiling point, when the
water gets to 210 there is a problem that needs to be fixed. In my opinion
the ideal temperature is 180, this heats the engine and allows a cushion for
slow traffic and up to 200 degrees. In slow traffic on hot days the fans on
most old Fords don't provide enough air through the radiator, getting out of
traffic and increasing the forward motion of the car allows forced air to cool
the water. Radiators with the over flow tube coming from the filler neck can
be fitted with a 4 lb pressure cap. Early radiators with the over flow off the
top tank of the radiator can use a 3 lb check valve supplied by Skip Haney.
With a proper working 4 lb cap or the 3 lb check valve the water can be filled
up into the filler neck and remain filled for a year or more. When I say working
pressure cap that means one that the rubber bottom end of the cap hits and
seats down on the washer like seat in the bottom of the filler neck. The long
large diameter hoses will take up the small expansion of water below 210
degrees, cap or valve releases pressure above that. G.M.
 
You don't have to run temperatures any higher than normal 160-180 deg. to use a pressure cap.
The pressurized recovery system that I am using consists of a recovery pressure cap and a recovery tank connected to the overflow tube.
Any overflow when at high temperature flows into the tank and as the engine cools it draws it back into the radiator.
This is the same basic system that has been used on newer cars for many years.
 
From the 1949 - 52 Ford F-Series shop manual:

"The cooling system used on trucks is the pressure type, having a regulated pressure of 3 1/2 to 4 1/2 pounds maintained in the system while in operation. With this pressure system, the coolant is allowed to reach a higher boiling point. This higher coolant temperature reduces the loss of energy to the coolant and also assists in decreasing internal friction by maintaining a higher lubricating oil temperature."

The earlier engines were originally designed to operate at lower engine temperatures and unpressurized cooling systems. But they will benefit from higher coolant temperatures, I would consider 180 degrees as the low end for engine temps and personally prefer something more in the 185 to 190 degree range.

The overflow systems are a big advantage regardless of the normal engine temperature!
 
Last edited:
Blu Dice said:
I'm dumb - why would you want that to happen?
Click to expand...

Hi Everyone, as stated, the boiling point increases 3 degrees for each PSI of pressure.

Modern vehicle © 15 psi, water now resists boiling for 45 degrees over non pressurized system.

Also why it's dangerous to remove cap from pressurized system, when pressure is lost fluid happily not boiling goes right to steam when depressurized.
 
VeryTangled said:
Hi Everyone, as stated, the boiling point increases 3 degrees for each PSI of pressure.

Modern vehicle © 15 psi, water now resists boiling for 45 degrees over non pressurized system.

Also why it's dangerous to remove cap from pressurized system, when pressure is lost fluid happily not boiling goes right to steam when depressurized.
Click to expand...

Why does the boiling point keep coming up?? These engines should never
get over 210 or 5 lbs pressure. G.M.
 
G.M. said:
Why does the boiling point keep coming up?? These engines should never
get over 210 or 5 lbs pressure. G.M.
Click to expand...
Thought it was the radiator/heater core construction that limited the pressure that the system would handle and not the engine?
 
34PKUP said:
Thought it was the radiator/heater core construction that limited the pressure that the system would handle and not the engine?
Click to expand...

I tried a 10# cap on my first Pike's Peak climb to try to keep the water in with such low air pressure. It just blew the water out around the hoses and other weak points of the cooling system not designed to handle that much pressure. Ford's designation of a 4# cap, at least for the 59A engine that I have, is just right. It raises my boiling point 12 degrees, which is usually plenty for most of my driving.
 
34parkup, you are correct. Very tangled, I was taught 4 degrees fahrenheit for every 1lb increase in pressure from atmospheric pressure (sea level)

A point that hasn't come out yet is that you do not want your engine to boil.

If it boils, there is local overheating at the point the steam bubble grows from.
The temp rises there and cracks can occur as a result of big temperature differences.

As mentioned by JSeery, a rise in the normal operating temperature of an engine means it is more efficient (a petrol engine is only about 26% efficient, a diesel about 30%, and an electric motor about 90%, from memory)
The benefit of a pressurised system becomes obvious when you look at a system running a 12 pound cap. At 4 degrees per pound this system can run up to 260 degrees before it boils.
Dare I mention thermostats?
Thermostats maintain a minimum operating temperature (you can run too cold) and lenghten the life of your engine.
Early flatheads ran no stats and an open (unpressurised) cooling system. The later flatheads ran both thermostats and a pressurised (closed) system, along with which, came better reliabiity and a far greater engine life.
 
A benefit of a boiling point slightly over 212 (4 psi cap) is that an engine running at normal temps of 180 won't puke coolant when you stop, and cooling system temperatures rise. A very normal situation.

Water expands about 5% from 70 deg to 180 deg, so on a 22 qt system a recovery can has to be around a quart to hold that.
 
We run a 13lb cap on a competition 99 engine.We run truck pumps which have to be in very good condition and double clips on water pump intakes.It also recovers water from catch tank on cooling.Temp runs around 200f.I know we are pushing our luck and probably wouldn't work on a road engine. Geoff
 
The limitations of the pressure in the cooling system is set by the seals/gaskets so if you start raising it you will sooner or later end up having coolant in the oil or leaking out the pump sealings.
With a rebuilt pump with a modern seal you shouldnt have any more limitations then a modern car has.
Hoses and radiator aint different just make sure they are in good shape.
 
34PKUP said:
Thought it was the radiator/heater core construction that limited the pressure that the system would handle and not the engine?
Click to expand...

The top tank on the radiator is the thing of most concern when the
old Fords get hot. Modern tanks are round to take more pressure.
The old radiators have large surfaces of flat metal and the tanks
surface gets bulged and stretched plus seam solder joints open.
The temperature should never get over 210. Forget raising the
boiling point it serve no purpose. G.M.
 
Some military Fords were running pressurised systems in 1941 and because they had an issue with bursting seams an upgraded radiator was introduced with a wider seam.
War caused technology advances to move fast.
 
You must log in or register to reply here.
Back
Top