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Old 05-25-2015, 05:16 AM   #1
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Too much pressure in coolant tank

I have been struggling for over a year with an issue with my 01 Boxster S Tip. Condensation under trunk lid over the coolant cap. I am on my 6th 04 cap. Never overheats. No water in oil or oil in water that I can detect. Level stays pretty consistent. Pressurized tank to 20psi for 24 hours. Pressure tested cap, pops at 20.5.



Getting desperate, I left the pressure gauge on the car and started it. After it warmed I got 20psi, (which is enough to pop the cap valve apparently.)



Again, the car does great even in Texas heat. It just vents through the cap... any ideas?

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Old 05-25-2015, 05:38 AM   #2
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The pressure is generated from the effect of temperature on the coolant, so my only thought is it is getting too hot or the coolant mix is responsible for the excess pressure. Have you cleaned your radiators and are you using the correct coolant mix?
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Old 05-25-2015, 05:44 AM   #3
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Other thoughts are a stuck closed thermostat or degraded impeller on the water pump.
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Old 05-25-2015, 06:58 AM   #4
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Thanks James! Mixture is dead-on, radiators clean, no signs of high coolant temps, temps verified by Durametric. Have Airlifted, pressurized, and spent a fortune on tools and caps... still have the problem. Dealer says it is OK. Shrug...
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Old 05-25-2015, 02:14 PM   #5
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Is the pressure relief valve leaking (located under the plastic cover below the coolant / oil fill caps)?
If you remove the plastic cover and see residue, its a good sign that the O rings are leaking when hot. You can try lifting the chromed D ring to its vertical position for a few days heat /cool cycles to make sure its not leaking condensation from the valve area.
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Old 05-25-2015, 02:39 PM   #6
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Steve, no residue at all. I replaced the orings twice...
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Old 05-25-2015, 03:12 PM   #7
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Anybody have s coolant flow schematic? I wonder if a restriction downstream of the tank could raise the pressure in the tank. A wild guess to be sure, but the options are thinning down.
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Old 05-25-2015, 03:28 PM   #8
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Found one.

Looks like there is a shut off valve (#10) on the tank inlets



Perhaps another forum member with experience can comment on what happens if the inlet valve sticks open.
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Old 05-25-2015, 05:12 PM   #9
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That's the spring loaded expansion valve located at the top of the tank....
bglz - I still would try lifting the mechanical D ring for a few heat cycles.
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Old 05-26-2015, 03:14 AM   #10
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Thanks Steve! I have tried that multiple times. Still venting through cap.
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Old 05-26-2015, 02:19 PM   #11
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If you have excess pressure in the cooling system then the pressure must be coming from somewhere.
1)It can't be the pump as I doubt it could compress up to ~ 20psi even with near boiling point water.
2) It could be a blocked engine / radiator vent line (#11 & 12 in diagram) but ??

I'd hate to think that you have a cylinder head crack opening up when hot and combustion gasses are "pumping up" the cooling system....
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Old 05-26-2015, 02:26 PM   #12
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Quote:
Originally Posted by Steve Tinker View Post
If you have excess pressure in the cooling system then the pressure must be coming from somewhere.
1)It can't be the pump as I doubt it could compress up to ~ 20psi even with near boiling point water.
2) It could be a blocked engine / radiator vent line (#11 & 12 in diagram) but ??

I'd hate to think that you have a cylinder head crack opening up when hot and combustion gasses are "pumping up" the cooling system....
This is exactly what I posted to the OP on another site (http://www.renntech.org/forums/topic/48478-too-much-pressure-in-coolant-tank/), and suggested running both a leak down on the engine and checking the vapor above the coolant in the tank for combustion gases using one of these:



That excess pressure is coming from somewhere other than the cooling system.....
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Last edited by JFP in PA; 05-26-2015 at 02:29 PM.
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Old 05-26-2015, 02:58 PM   #13
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Thanks guys! I am just grasping at straws here, hoping for a different answer, LOL! I just cannot understand it...
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Old 05-26-2015, 04:46 PM   #14
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JFP, thanks for your answers. It is not that I didn't believe you...I just was hoping for another verdict, LOL! Sort of like getting another opinion when the diagnosis is cancer!
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Old 05-26-2015, 05:09 PM   #15
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JFP, thanks for your answers. It is not that I didn't believe you...I just was hoping for another verdict, LOL! Sort of like getting another opinion when the diagnosis is cancer!
There are only a limited number of ways to get a cooling system to over pressure; over heating is the obvious one, but a combustion pressure leak into the cooling system is also a reality.

To use your cancer analogy, it is time to stop speculation and start diagnostics. A leak down will show if one or more cylinders are losing gas pressure, the presence of combustion by products in the cooling system would also be a dead give away. If neither of these check out positive, you will have eliminated a major probability and can move on to look at the cooling system itself.

But you have to start someplace.............
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Old 05-26-2015, 05:13 PM   #16
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Same problem

I just replaced cap and o ring and still having problem. Could it be fixed by replacing the entire valve?
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Old 05-26-2015, 05:28 PM   #17
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Watery

If the coolant mix was slightly watery would this cause the condensation?
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Old 05-26-2015, 06:05 PM   #18
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Thanks! I will take it in to an indie. I have spent a fortune on tools, caps and fluids, and spent a lot of time trying to diagnose the problem. I give up.
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Old 05-29-2015, 11:09 AM   #19
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Quote:
Originally Posted by Steve Tinker View Post
That's the spring loaded expansion valve located at the top of the tank....
bglz - I still would try lifting the mechanical D ring for a few heat cycles.
Did this fixed the condensation problem. Thanks Steve

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