Exactly what the title says. I haven't added coolant or anything. Thought I would check the rad level and there was still pressure at the cap. It actually put some coolant in the overflow bottle. This sounds weird to me, maybe bad rad cap?

Dave

I have not seen this, so this is a guess. First, the logic. You start with an open system, fill it with fluid and cap it. Run the car, the temperature comes up and the pressure comes up because the system is sealed. Shut of the car, then when the temp comes back down, the pressure comes down and you return to the beginning state.

So now the guess. What can change the end state from the beginning state? A drastically cooler ambient temperature. A drastically lower altitude (which is the same as ambient pressure). Or introduction of some additional substance --- like combustion gasses caused by a head gasket leak.

I have not seen this, so this is a guess. First, the logic. You start with an open system, fill it with fluid and cap it. Run the car, the temperature comes up and the pressure comes up because the system is sealed. Shut of the car, then when the temp comes back down, the pressure comes down and you return to the beginning state.

So now the guess. What can change the end state from the beginning state? A drastically cooler ambient temperature. A drastically lower altitude (which is the same as ambient pressure). Or introduction of some additional substance --- like combustion gasses caused by a head gasket leak.

I'm going with ambient, outside, temps have gone up since it cooled down from a week ago.

Weird huh, you think if the head gasket was on the way out, it would loose pressure sitting for a week.

Dave

Sounds like a bad cap to me. Maybe it is not letting the overflow out to the recovery tank.

Sounds like a bad cap to me. Maybe it is not letting the overflow out to the recovery tank.
I think it may be that,seems the system is sound,no leaks,so maybe the cap is stuck closed.the temp change can do it to,just like a fuel tank-
rth

Its a closed system with no over flow tank.

Dave

Its a closed system with no over flow tank.

Dave

does the car run good? not over heating?? no oil in water? vise versa.
no white smoke out exaust?????

rth

Are you sure you dont have the opposit going on when the cooling system cools down and the coolent lvl drops a bit which can at times in a tight system actually pull a slight vacuum?

Then if the the case it will still make a sucking noise when you initally release the rad cap which can easily be mistaken for pressure being reased when it's actully the vacuum noise of the cooling system comming back up to atmospheric pressure when you release the rad cap .

But a stone cold cooling will not be presurized under normal circumstances.

Scott

If it had a vacuum would it still come out of the overflow hose? The car runs perfect not overheating.


Dave

Dave,you dont give enough info, what the exactly do you mean when you say coolent is comming out of the overflow hose?

* DOES COOLENT COME OUT OF THE OVERFLOW HOSE WITH MOTOR HOT AND RUNNING & OR IDLING?

* DOES COOLENT COME OUT OF THE OVERFLOW HOSE WITH MOTOR HOT BUT JUST AFTER SHUTTING IT DOWN?

* DOES COOLENT COME OUT OF THE OVERFLOW HOSE WITH MOTOR COLD WHEN YOU OPEN THE RAD CAP?

* OR IF COOLENT DOES NOT COME OUT OF THE OVERFLOW HOSE UNDER ANY OF THE ABOVE CONDITIONS THEN WHEN EXACTLY IS COOLENT COMMING OUT?

But to generally ans your question with motor hot yes coolent can come out of the overflow hose with a non recovery type system esp if it's overfilld ,has wrong and or old/weak rad cap,or if its running hotter then you realize.

In a std non recovery type cooling system like out old cars have there can still be some residual coolent in overflow hose with a non closed system if a little coolent spits out when you 1st shut it down as ,mantioned above. Then when it cools off there can be a small vacuum created that will hold some coolent in the overflow hose & or inside the filler nech untill you open the cap to vent the radiator & releasing the vaccum from the system and any residule coolent left in the filler neck area will then exit out the overflow hose when the vacuum is released from the system .

But with a closed recovery type cooling system like todays cars run when its cold there will be coolent in overflow to tank hose too. In those systems coolent moves from the recovery tank to rad when system/motor cools off and then when the coolent/motor heats up again the coolent moves from the radiator to the recover tank because coolent expands when heated.

If your running a stock cooling system with no recovery tank and the radiator overflow hose just hangs out in the open draining onto the ground make sure the coollent lvl is approx 2.5-3" from the top of the rad filler neck to ensure there's enough room for coolent expansion.

Coolent any closer to filler neck then 2.5"-3" will come out of the overflow hose when it heats up & expands and then you shut it down.

And again,a stone cold cooling system & cold motor should not have pressure in the cooling system.

If you shut down the motor hot and then pop the rad cap off 1hr or maybe even 2 hrs later there could be a little pressure left in the cooling system esp on a hot day.

But when the car/motor sits overnight getting stone cold there shuld be no pressure in the cooling system,vacuum in the system is possible at that piont but no pressure should be present.

Scott

Sorry for the confusion, its the old style cooling system with no overflow bottle. It sat for a week with no running. A week later I pulled the cap off to check the level, it felt like pressure when it went to the first stop when you remove the rad cap. When I went to the first stop I heard a hiss of air and coolant came out the overflow tube on the ground. I find it weird why there was pressure for sitting a week. It could of been vacuum I guess like you mentioned but if it was vacuum would coolant come out?
When hot or idling there is no coolant coming out the overflow.
Dave

Dave, I am having the exact same problem, even after setting for a week if I take the cap off it will overflow out of the cap hole. I am replacing the cap and the overflow hose tonight and will let you know if that is it. I do have an overflow tank that has stayed exactly the same level. I have a 160 thermo and it wants to run 195 when it warms up. I want to run a 180 thermo but cant until I figure this out. I am running 2 electric fans and have the option of running them constantly or off the thermostat. with the above scenario I have been running them constantly.

Jamie