The cap has two valves in it. One is the rubber faced spring loaded metal cup that holds the 13psi radiator pressure. In the middle of the wet part of the main part of the cap is a small dime sized metal disc. This is a one way check valve that holds radiator pressure with the main valve, and under very light spring loading, allows the partial vac in the cooling system to pull water back in from the recovery tank. Remove the cap and make sure the little disc can be lifted with a fingernail. Make by blasting with a hose that the line from recovery tank to radiator neck is clear and not obstructed by the cap seal. There are two seals for the cap. One seals the top of the neck with a positive clamp seal as the cap is tightened, and the other seals the lower radiator neck with spring pressure up to the cap pressure rating. The lower seal is broken by pressure as the radiator vents to the recovery tank in a temp overheat or hot soak, and the little central valve lets the water back into the radiator as the system cools and the partial vacuum builds.

I bet the bottom hose is getting weak. 10yrs is way too old.

If the upper hose, heater core hoses, and cap haven't been changed in that much time, it might be a good time to replace them as well. <img src="/forums/images/graemlins/cyclops.gif" alt="" />

both, thank you very much for the info. I will have a closer look.

oh, and cap is new, hoses are not.

After reading all this i still say you must of bought a defective radiator cap dealer or not.Does your lower radiator hose have the spiral spring inside of it if not you should replace it with one.Does it collapse at higher RPMS?

it only collapses when engine is cooling..........no spring.

ok, attention smart people:

turns out, that there was a lot of sediment in bottom of overflow bottle blocking the tube, I just changed the coolant and it still looked nice, this truck has some serious sediment issues.

question 1: can mixing of green and orange coolant cause it to form sediment? I think previous owner had mixed them.

question 2: can sediment trapped in heater core cause the water rushing sound i hear in the dash?


I had the system power flushed and there is still a rushing sound from under the dash, dealer thinks it is the heater core.

he told me there was tons of sediment coming out of it, almost as if someone poured sand into the radiator.

would that get caught up in the core and cause that sound?

lastly, at this point, is there any other part of the cooling system that should be replaced since it was so plugged up with sediment? since it is apart to get the heater core, I want to make sure the whole system gets taken care of and we don't put in a new heater core just to get it plugged up again with sediment traveling over from another part of the system. should I replace the radiator and water pump while I am at it?

Your not supposed to mix the green and orange.

http://bioengr.ag.utk.edu/Extension/ExtProg/Machinery/Articles/engcool.htm

As this engineer states "The organic acids in orange types will cause precipitation of silicates in the green type"

You need a serious system flush. I would remove the thermostat and garden hose it for a while. If you can get to the heater hoses, I would power flush that also with a garden hose.

Be careful not to spill any antifreeze depending on your local regulations.

If it's really bad, I would have the radiator boilded and flushed at a radiator shop. Whatever it takes to get that crud out. <img src="/forums/images/graemlins/patriot.gif" alt="" />

Probably have a lot of it sitting at the bottom of your block too. <img src="/forums/images/graemlins/frown.gif" alt="" />

ok, so do I need to replace the heater core or radiator or will a bunch of good power flushes get everything out in time?

also, does anyone know if the gen II or gen II.5 monteros have a constant flow heater core system or does it have a valve inline with the heater hoses? I know both exist, just not sure how the montero is setup.