Radiator Cap vent returns

[Ecomike]

My 85 XJ-Mutant diesel has given me issues off and on for about 9 years now, with not wanting to draw coolant back into the radiator when it cools off. It is not the usual suspects.

I have never really trusted the radiator caps whose vent returns do not spring close. But I just discovered that the 87-95 jeeps use the caps with the floating (no spring to close) vent on the bottom.

I am wondering if anyone in Naxja has ever researched the two different styles of vent valve and learned anything useful, like if a radiator hose is soft, will it keep the spring from opening and letting coolant from the overflow back into the radiator. Also what is it that actually closes the loose valves, is it buoyancy, or flow, or what? I use to think the ones with loose valves were just defective, but it seems there are two styles.

Here is a link that discusses the two styles, but nothing I can find on the internet explains why there are two styles.....etc.

http://installer.aed-inc.com:8191/Stant Technical Info/TempTalkRadCap_4.htm

 

[Ecomike]

From the link I posted in post #1:

The normally closed type of vacuum relief valve is used in a "Constant pressure" type cap. With this design, the vacuum valve is held shut by a very light spring, creating a totally sealed system. When the engine is started and begins to warm up, coolant pressure starts to rise immediately because the closed vacuum valve prevents pressure from escaping as the coolant expands.

With caps that have the open variety of vacuum valve (called “pressure vent” caps), there's no spring to hold the vacuum valve shut, only a small calibrated weight. When the engine is first started and under light operating conditions, pressure can vent through the vacuum valve. This allows the cooling system to operate at atmospheric or minimum pressure, which reduces strain on the water pump seals, hoses, radiator, and heater core. As the engine starts to heat up, the escaping steam or coolant pushes the vacuum valve up and shut. This seals the system tight and makes the cap function like a constant pressure type of cap.

When the engine is turned off and cools down, vacuum inside the radiator allows the weighted vacuum valve to reopen. This type of vacuum valve design can also allow the water pump to pull additional coolant into the radiator if the cap is located near the radiator hose that connects to the water pump inlet.

 

[Ecomike]

Well I switched to the radiator cap that does NOT have the spring to close vent and the problem has gone away. No head gasket leak, holding good pressure, and no coolant loses. So I guess I learned something here.