RACING PRESSURIZED RACE CAR COOLING SYSTEMS can improve aerodynamics by allowing cars to run temperatures as high as 265 degrees.
How high can I run my water temperature?
What type of radiator can I use that will accept high pressures?
By Jean Genibrel
Pressurized cooling systems are becoming ubiquitous in racing and off-roading. Indy Cars, Formula Ones, NASCAR cars have used this type of cooling system for some time now with great success.Pressurized cooling systems are finding acceptance in off-road racing, short track, and road racing.
Properly designed pressurized cooling systems, such as those manufactured by C&R Racing, utilize an accumulator which is similar to a surge tank, but it is built to sustain higher pressures, and it acts as an air spring. Water accumulators contain a pressure relief valve and a sight gauge to help in bleeding the system, a line from the suction side of the water pump and a return hose from the radiator. The tank comes with a Pressure Relief Valve (PRV). The PRV is adjustable, so it eliminates the pressurized radiator cap. The accumulator is also accompanied by a quick disconnect fitting for the operator to add some pressure to check for any air trapped in the heads.
This drawing from Evans Waterless Engine Coolant identifies the areas most prone to boiling in the heads. These spots reside above the combustion chamber and the exhaust port. Once the water reaches Critical Heat Flux, the steam creates a barrier between the metal and the coolant. This condition can lead to preignition, detonation, pinging and severe engine damage. A system with an adjustable pressure valve will permit the pressure to increase to a preset level and to avoid boiling the water.
A water pressure gauge (and warning light) can give the driver an idea where his car cooling system stands. The temperature should increases at the same rate as the cooling system pressure. When a hose blows or a leak begins, the driver can spot the problem before losing control of the car in the leaking coolant.
About Pressurized Cooling Racing Water Systems
From C&R Racing
Pressurized water systems are relatively new to the short track and stock car world. This technology has been around in F-1 and Indy Cars for many years. C&R has been involved with the pressurized cooling systems through our Indy Car customers since it’s inception. It’s more efficient and more failsafe than the conventional closed cooling system that has been around for the last 80 years. This is the future for cooling systems that will make it’s way into the stock car and short track arenas over the next few years. (Since C&R published this piece, their pressurized cooling systems have made headways into off-road racing and drag racing. ed)
Pressure in a cooling system is vital for keeping water in contact with the metal surfaces of the cylinder heads and block. Pressure keeps the air compressed and maintains the water to metal contact that is vital to prevent localized boiling or steam pockets in the combustion chamber areas of the cylinder heads. When a situation occurs that causes temperatures to rise such as lean fuel mixture, too much ignition advance, or a clogged radiator, the air in the water will expand and form small steam pockets. This will start in the combustion chamber area (hottest spot) and the steam pocket will be attached to the metal surface. These spots get very hot and since it’s in the combustion chamber area, it will create a detonation problem. Therefore, engines lose power when overheating occurs. Once steam starts in the cooling system, the problem will magnify and continue to get worse.
By keeping adequate pressure in the system, the boiling point will be high enough that this overheating situation can be prevented. The higher the pressure the higher the boiling point. For instance, at sea level with a 30 lb. cap the boiling point would be around 265 degrees. That’s why we always recommend a 30 lb cap for racing. With our pressurized system, we use an adjustable pressure relief valve instead of a radiator cap. We do this because it will go higher than 30 psi. The other components in this system are an accumulator and a tool to set the pressure in the system. The accumulator is a can, similar to a header tank, that the air bleeds into from the cooling system and this can also has a controlled air space that acts as an air spring. This air spring will compress under temperature expansion and keep water from going out the overflow. It keeps the pressure in the system and is the place where the system pressure is set.
The boiling point increases as the pressure in the system rises. The critical point to avoid is the nucleate state where the steam bubbles can explode and cause damage to the engine and create preignition.
“If the heat flux of a boiling system is higher than the critical heat flux (CHF) of the system, the bulk fluid may boil, or in some cases, regions of the bulk fluid may boil where the fluid travels in small channels. Thus large bubbles form, sometimes blocking the passage of the liquid. This blockage results in a departure from nucleate boiling (DNB) in which steam bubbles no longer break away from the solid surface of the channel, bubbles dominate the channel or surface, and the heat flux dramatically decreases. Vapor substantially insulates the bulk liquid from the hot surface.
The pressure in a cooling system is vital for keeping water in contact with the metal surfaces of the cylinder heads and block. Pressure keeps the air compressed and maintains the water to metal contact that is vital to prevent localized boiling or steam pockets in the combustion chamber areas of the cylinder heads. When a situation occurs that causes temperatures to rise such as lean fuel mixture, too much ignition advance, or a clogged radiator, the air in the water will expand and form small steam pockets. This condition starts in the combustion chamber area (hottest spot), and the steam pocket will be attached to the metal surface. These spots get boiling, and since it occurs in the combustion chamber area, it will create a detonation problem. Detonation is why engines lose power when overheating occurs. Since race car cooling systems are not designed to cool steam, Once steam starts in the engine, the problem will magnify and continue to get worse.
C&R Racing manufactures most of the radiators used in NASCAR Cup racing. With those teams, C&R engineers have been able to develop a pressurized system that has allowed some engines to run as high as 290-degrees F. The system is composed of a purpose-built radiator, a pressure tank, and a pressure relief valve at the top of the reservoir. The gauge on the right is used to check for air in the system at the time of the installation. The assembly from APPLIEDSPEED.com also comes with a pressure regulator to install the small amount of pressure intended to check for air trapped in the system. The kit also comes with a quart of C&R’s Safe Coolant Corrosion Inhibitor additive.
What are the advantages of a pressurized system?
With a pressurized system, the engine can operate at higher temperatures safely. In the case of an Indy Car or F-1 car, it means that the air ducts to the radiators can be smaller and thus more aerodynamic. On a Sprint Cup or road race cars, tape can be applied to the grill opening making the cars more aerodynamic by reducing the quantity of air that becomes trapped in the engine compartment. There is a bigger safety margin for error such as clogging the radiator or running too lean on fuel mix. You can run leaner for power and not be in the danger zone of overheating. As an example, most F-1 teams will run cooling system pressures as high as 50psi and will race all day with temps at 265 degrees.
When filled, the accumulator should contain an air space above the water level to act as an air spring. Since water does not compress, but it expands with higher temperatures, the air spring allows the expanded water to squeeze the air without lifting the PRV. If the system is all water and no air spring is present, the PRV will lift during the temperature expansion cycle. The PRV setting in relationship to the size of air spring, water volume, and the amount of pressure added at ambient will determine the maximum water temperature possible without opening the PRV. Some teams are running as hot as 290°F (and 60 to 70 PSI) with the C&R system on a regular basis without opening the PRV.
The air spring possesses an additional feature. To check for complete bleeding of any air, the system is first filled with water, the engine is operated at low to medium speeds for several minutes, and the level is checked again on the gauge. A drop in the level means that there is some air in the system.
FROM C&R RACING'S INSTRUCTIONS
Fill cooling system with water and a water conditioner such as Safe Water Conditioner. Remove –12 port plug from the top of the accumulator and top off with water. Depress poppet on quick disconnect so that the air spring cavity will fill 75% with water leaving upper 25% as air space. MAKE SURE THAT THE SCREEN ON THE –12 PORT BUNG IS CLEAN (Where Applicable)Click on this video for more information
- Run the engine with –12 port plug removed until all the air has bled out of the system. Fill accumulator with water to the top of –12 filler leaving no air space. Replace –12 port plug and warm the engine to approximately 180 degrees.
NOTE: Using water circulator will help purge air from the system.
Connect pressure filling tool to quick disconnect fitting. Increase pressure until water pushes through PRV (Approximately 35psi). Push water out until level on sight glass is at half way point. That point is the operating level.
NOTE: During this step of setting the water/air spring level in the sight glass you can see if there is any air trapped in the cooling system.
If the level in the sight glass is at halfway and when adding pressure the water level drops substantially or even disappears, there is an air pocket somewhere in the cooling system. Air will compress causing the water level in the sight glass to drop. When you take the pressure off, the water level will come back into the glass.
Circulate the water by running the engine or use the water circulator (Appliedspeed.com part number 60-00002 ) to bleed out the air. When the system is properly bled, the level in the sight glass should only drop ½-inch or less upon applying pressure.
“Air will compress, water will not”. This is an ideal way to test for trapped air. After setting level in sight glass at halfway, bleed pressure down to 15psi. 15 psi is the starting pressure with a 180-degree engine temperature.
- Fill cooling system with water. Plug in water circulator and circulate to remove air. Depress poppet on quick disconnect to bleed air from air spring cavity and fill to top of sight Fill accumulator to the top and replace –12 port plug.
- See step 3 under race day procedures.
- After setting level in sight glass, bleed to 5-8psi. This will be a starting point for qualifying with a cold engine and cooling system. This number is based on starting with a “cooled off” temperature of 50°F.
ADVAMACS.com publishes this handy "Boiling Point Calculator": http://www.trimen.pl/witek/calculators/wrzenie.html
Do not attempt to run higher pressures than your radiator is designed. Purpose-built radiators from C&R Racing contain reinforced tubes, and they are welded with the proper techniques to hold high pressure.
Do not pre-pressurize your cooling system. Instead, allow the system pressure to build on its own from the engine heat. The C&R instruction video will guide you on how to check for air in the system by installing some initial pressure.