At Evans Cooling, our technical team is always working on ways to help the many users of our waterless coolants. Here are some of our best technical tips.
Tech Tip: Decreasing System Pressure
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
- Thermostat design
- 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 pressurizes 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 100° C, 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 125 degrees C. 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.
Tech Tip: Coolant Pump Drive Ratio
Do you know your coolant pump drive ratio? You can find it by dividing the diameter of your crankshaft pulley by the diameter of the water pump pulley.
8” crank /6” pump = 1.333, or 33% overdrive for the pump. 4000 engine RPM would be about 5300 RPM at the pump.
A figure less than 1.0 would indicate an underdriven pump.
6” crank /7”pump = .85, or 15% underdrive. 4000 engine RPM would be about 3400 at the pump.
Generally, overdriving the pump will give better cooling system performance in a street car. (OEM ratios are often 25% overdrive or greater) A street/strip, road racing or off-road application which sees sustained high RPM, should underdrive the pump.
Coolant pump performance is affected by driven speed, also by radiator type, and by restrictions such as thermostat type and hose size.
Tech Tip: Storage of Used Evans Coolant
Evans Waterless Coolants are hygroscopic. Hygroscopic is defined as "tending to absorb moisture from the air." When working on a system containing Evans Coolants, the coolant should be drained then stored in a sealed container. If possible, the openings of the system should also be blocked or plugged to limit exposure of the remaining Evans Coolant to the atmosphere. Always recheck the coolant water content before reinstalling with a refractometer or test strip.
Tech Tip: Thermostat
The thermostat in an engine cooling system has two purposes; The first is temperature control and the second is restriction. Thermostats are typically located in one of two places, the upper hose or the lower hose. Upper hose locations control the coolant leaving the engine, typically a higher temperature is used, and more restriction. Lower hose location controls incoming coolant to the engine; The temperature and restriction is typically less than the upper hose location due to heat absorption through the engine. Temperature control is determined by the OEM or the DIYer, per the application they are building.
Today's OEM engines use many thermostat designs and the aftermarket has different designs for most applications (high flow, bypassing, fail safe, balance sleeve). Removal of the thermostat is possible on some applications BUT NOT ALL! Evans High Performance Coolant can take advantage of the different design thermostats or removal of the thermostat when possible, due to a higher boiling point than water or 50/50. Carbureted engines can benefit from lower thermostat setting, but computer-controlled fuel injection typically requires temperature control in a specific range. For more information on your application please contact Evans Cooling Systems.