Automotive cooling systems use “system pressure” to affect cooling functions. The action of the pump pushing coolant through the engine against restriction creates pressure.
This pressure varies with engine rpm when a crank shaft-driven pump is used; An electric pump maintains a constant pressure or varies the pressure related to engine temperature. System pressure can be as high as 40psi or more at the engine outlet/cylinder heads or as low as 5psi at the pump inlet during idle. A pressure drop, through the radiator core, accompanies the drop in temperature of the coolant
System pressure is affected by:
- Engine design
- Radiator configuration
- Waterless coolants provide sufficient heat transfer, boil at a higher temperature, and are non-corrosive.
- Hose size
- Pump output
The only way to change this pressure is to increase/decrease pump flow or add or remove restriction from the system.
The water component of coolant boiling, in the hottest areas of the engine, creates expansive vapor, which further pressurises the system. “Cap pressure” refers to the amount of liquid and vapor pressure held in the system at the cap location. This is the only pressure that is obvious to everyone, it’s stated on the radiator cap. Depending on the location of the cap it can be as low as 4psi or as high as 35psi.
The boiling point of water, normally 212° F, is raised 1° F for every 3 psi. of additional pressure. A typical 15 psi. cap, will hold the water in the system up to about 257 degrees F. This does not mean there is no boiling in the engine up to this temperature, but it is the point, up to which the cap will contain the expansive nature of the vapor.
When using Evans Coolant in the engine cooling system these pressures can be decreased to maximize the system’s flow and temperature control capabilities. These changes are application specific and should be discussed before proceeding. Please contact Evans Tech Support at 1-888-990-2665 or firstname.lastname@example.org.