radiator caps and pressure in vehicle engines

[Thunderchild]

Say I ran a vehicle engine with a faulty radiator cap that was not holding pressure (ie: non existent) what would be the effect ? why are radiator systems pressurized at all ? or is the pressure release to keep water in but let pressure out as the water (and air) heat up ?

[ChuckFickens]

The water would boil and eventually evaporate away due to boiling. The radiator is pressurised to increase the boiling point of the coolant in the same way as a pressure cooker works.

[beso]

An engine can be damaged by a faulty radiator cap.

If the pressure rating is too low it may cause the coolant to boil inside the engine. This causes cavitation which can blast chunks out of metal, particularly aluminium parts.

I have seen this happen when the engine is turned off and no coolant is being pumped. The sound of boiing could be heard a few seconds after switching off. The cavitation damage was evident on the body water pump ultimately causing it to fail with a hole.

[chas2008]

there for a reason-

http://auto.howstuffw...m/cooling-system7.htm

[Martin2875]

Hi Thunderchild. Car engines run better when they're warm, but not too hot. Water normally boils at 100 degrees centigrade, but this increases by 3 degrees for every 1 pound of pressure. So a car with a 13 pound pressure cap will boil at 139 degrees. Running an engine with no pressure in the cooling system is not advised as every time the engine reached normal running temperature it would boil over. Cylinder heads would buckle and engines will crack. Expensive.