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Cooling System Operating Pressures: Article by US Radiator

Cooling System Operating Pressures
          Article by U S Radiator

Cooling system operating pressures are largely determined by water pump operating pressures and its prefered to keep it under 10 pounds. The two factors that will increase normal operating pressure are increased operating temperatures (not a good thing and indicates a need for more heat transfer) and high volume electrical pumps.  Increasing the pressure by 1 pound increases the boiling point by 3 degrees, so by running a 12 pound cap the water won’t boil until it gets to 248 degrees.  An engine that wants to run at 248 degrees will open that cap up long before it gets that hot.  To deliberately increase the operating pressure by way of an electrical pump to increase cooling is redundant and again only points out the need for more efficient heat transfer.

Pressures will increase in the system just after turning off the engine as the coolant absorbs existing engine heat but can’t move through the radiator to dissipate it. The resulting increase in pressure pushes coolant past the cap and hence the need for a coolant recovery system.  Once the coolant in the idle engine starts to cool a vacuum is created and another valve in the cap opens and prevents the radiator from collapsing a top tank but more importantly returns the coolant to the radiator so no outside atmosphere or air (contamination) enters the sealed system.  Unfortunately most aftermarket recovery tanks are smaller than the needed capacity and that varies with cubic inches and size of the engine.  Rule of thumb is to buy the largest one that will fit in the engine compartment and still look cool.   Check the recovery tank often and if you find it empty you know the size in inadequate.

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