Coolant system can't hold any pressure
 

Hey, all --

I'm hoping you can help me figure this out:

New to me 2000 Boxster S. Previous owner reported an overheating issue, and the water pump was replaced by a Porsche-friendly indy shop. Still had temp issues -- the shop said bad head gasket and the owner then parked it for two years deciding what to do next.

Issue: I can't get it to stop ejecting coolant out of the tank's overflow.

It has a new (German) coolant expansion tank and it has a new '-04' cap on the tank, both from Pelican. I've flushed and refilled coolant and performed the usual air bleeding routine several times. If I run with the bleeder valve open, it will drizzle coolant constantly. If I rev the motor, upon deceleration it will eject a large volume of coolant. When I shut down the vehicle hot, it will dump even more coolant. If I close the bleeder valve, I will get steam coming from the overflow area when the car heats up (and it still dumps coolant).

I tried to pressure test the new tank, and I can't get it to pressurize at all. If I plug the overflow tube and just blow air into the coolant fill opening, air comes directly out of the overflow hole (what leads to the overflow tube - between the bleeder valve and the fill cap). This happens immediately -- it doesn't build any pressure first. No matter what I try, the coolant system won't hold any pressure.

Thoughts?

One other note:

The old (cracked) coolant tank seems to have the same issue. It's out of the car - if I plug all of the holes with my fingers, air just pours out the overflow hole. It doesn't build pressure at all it just comes straight out.

I'm so confused!

sounds like head gasket to me...
it should not eject coolant at all. There might be some burp or level rise, but not spitting.
Spitting would suggest air coming through.

Not sure if that could work here, but on other cars the best test was to rev the engine (coolant would rise and spit) and let off the gas (level would drop and some coolant would be gone).
The former says gases get through the gasket, the latter suggests liquid got sucked into the engine.

If it was overheated - it is hard to judge what exactly it means.
Was it 120 C for a couple of minutes or was it 150 C and coolant was gone? Engine will work OK with coolant is even at 150 C, but the coolant must be present in liquid form.
Once it starts evaporating - well, no more cooling there.

The seam on the side of the coolant tank where the manifold and hose connections pass through can cause the symptoms you describe if the tank is not properly assembled from the manufacturer. It would be a major coincidence for this to be common to both tanks, but this is where I'd check first. This is where saving money and not buying a genuine part can cost more in the long run in both money and frustration.

Even if the tubes were blocked off, shouldn't the tank itself be able to hold at least a little pressure? It's boggling me that if I just put my lips on the coolant fill tube and blow, it just blows right back at me through the overflow hole. Shouldn't it hold pressure to something like 14 pounds before the overflow opens?

My coolant tank had lots of "spider cracks" that were invisible until the coolant got hot and the system's building up of pressure would cause those cracks to expand and leak all over.

Solution.....NEW TANK! (the original tank was 18 years old)

I had major overheating issues that startedwith the thermostat.
The hot coolant cracked the heater valve and while in there we pulled the water pump which had no impeller
Blades left. Now it runs 180 to 190 on very hot 90+days

I am burping the system with the
Clip.i added some coolant but will.likely need more, that even lowered the temp a scootch. Funny too the car just runs better.


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As goofy as this may sound, you need to find someone with the vacuum filling system and pull a vacuum on the system. If you have air trapped in it, it will all "burp" out under vacuum; if it does, top off the system with a 50/50 mix by using the vacuum system to pull it in.

if the system does not "burp" out any air, or refused to hold vacuum, something in the system is leaking (cracked head, etc.) and further digging is required.

I am a bit [emoji32] of the Head Gasket.

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The head gaskets in the M96/97 are multilayer steel and actually stronger than the cylinder head or block, which is why you never see them failing.................

The head gasket is an easy test - buy an exhaust leak detector kit on Amazon or harbor freight. Fill the test tube up with blue dye, stick the tube on to the coolant fill port, rev the engine, and pump the ball on the test tube. This sucks gases out of the coolant tank and if there are combustion gases present it turns yellow.

FWIW I just went though a similar process. Coolant spewing EVERYWHERE from overflow tube with every drive. The burp valve was bad and needed replaced. Also, I'm convinced that I somehow overfilled the coolant system. As you pressurize the system it forces the coolant level down, and if its overfilled then there's no where for it to go but out.

You are correct though, the system should hold 1.4 bar pressure without problem. At that point the bleed valve should start to rise like a turkey timer. Around 1.8bar it will actually start to bleed of excess pressure.

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Thank Ferry or whomever....

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As JFP suggested, this is going to be a good way of finding an issue. The vacuum systems to fill coolant are pretty cheap (under $100 for a decent one). Makes doing a flush & fill pretty quick too.

What if the head is warped due to overheating?
There is no good information evidence what the previous owner experienced/did.

These heads tend to crack before they warp.

Thankfully mine never leaked, but at its peak temp.it blew coolant out the cap.most drained.i have added a new cap, but the Tech told me the cap.I had was fine.

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Hey, folks -- just wanted to close the loop on this in case this turns up in someone's future search.

The problem ended up being a faulty coolant expansion tank. There was a small gap in the seal, letting pressure escape through the overflow passage. Replaced it with a new (Porsche OEM) tank and all is good.

The tank replacement job sucks bad on it's own, doing it twice is just adding insult to injury. If you have to do this job, get the OEM part!