bleed valve open when hot!
 

After driving my new (to me) '97 Boxster from the UK to Spain 3000Kms with no problems at all, a couple of days ago I had a coolant dump from the overflow area after taking it for a "drive it like you stole it" session over the mountains here in Tenerife. I let the car cool then refilled the coolant as per instructions I've found on here. Since I've done this the coolant has dropped by about a cupful every morning when I check it prior to use. I initially thought that it was an odd air bubble finding its way out of the system but after quite a long drive today I went to check the coolant level and noticed that the bleed valve is open on its own from pressure underneath it, now it has cooled it is now closed. There is no water under the carpets and no condensation on the boot lid or in the general area. Soooo is this correct for the valve to open itself and what could of caused the initial dump? I live 6000ft above sea level would the atmospheric pressure difference make any difference? Great forum by the way:cheers:

Yes, the valve opens up when the coolant is at operating temp.

Good, that's one less worry :) Any thoughts on what could cause the coolant dump? The guage needle was fractionally to the right of T.D.C and it only dumped when I had turned the engine off. Ideas please.

Sounds like you have a leak. Usual suspects are the water pump and the coolant tank. Get under the car and see if you have water around the WP pulley. Pull up the carpet in the trunk and if there is coolant on the floor, then its the coolant tank. If you still can't find it then have a pressure test done.

Don't fool around with this. Just a brief overheating on these motors can ruin them.

Everything San R said. My guess would be water pump. Pretty common, pretty easy. I'm a little mystified as to why it dumps when it is stopped and not while it's running but my guess will be that it is now running a little over hot all the time and your pump is just keeping up but when you turn it off any natural hot spots within the system just can't cope and cause the whole thing to spew.

Start by looking for leaks and then if you can't find one and your car has more than 50K go to a replacement water pump.

Thanks Jittsl, this is where I'm struggling to get my head round the problem. The car has only done 25000 miles and the radiators are getting hot so the circulation is ok, the fans come on and go off as they should. Ultimately I think my question is; if the bleed valve is open when the engine is at running temp. how does the system pressurise? As I am so far above see level if the system is open to atmospheric pressure the water will boil at a lower temp. So if the system is working fine when the engine is running the final heat transfer from the block with no circulating coolant may push it to its boiling point which is 10º F lower at 6000ft
I have owned a few performance cars and most of them heat up slightly above the norm because of the height above sea level and the steepness of the roads but this one has me confused.

Hmmm. I'm not sure either but a couple of things.

Firstly, the valve on the top is not full open as soon as you have it running. It is supposed to have a required pressure and only when this pressure is exceeded does it open (like any radiator cap). This can be bypassed by flicking the little trigger as I did when I last drained the system but in normal operation it should maintain a preset pressure.

Secondly, just because the radiators get hot does not mean everything is good. A faulty pump may move some (but not enough) water.

Thirdly, if you have set your water level to the recommended level, have then left the trigger open and made sure all the air is out by taking for a good hard drive and getting it to operating temperature, then closed the valve and you are still observing the water level going down on a daily basis then something is wrong. Choices are:
1) Water is leaking out either, all the time or when under pressure. Likely culprits include pump, reservoir, hoses, radiators or head gasket. Possible also that the cap or the overflow are not functioning properly and are not holding pressure and therefore allowing water to escape.
2) Engine is getting too hot and forcing water out the overflow. Likely culprits are bad pump, blocked radiators or not enough water in the first place.
3) Engine has blown head gasket which is causing 1 or 2. Only culprit is obvious.


For the one example I can offer you. My specBox runs in Texas temperatures (100+) in racing conditions and often shows 220+ on the gauge at the end of a race and I have not topped up the water since the motor was installed 2 yeArs ago.

Sorry I can't get at exactly why it puked but hopefully the above information will help.

Good luck, Laurie

Had something similar to this happen this spring. It turns out that the Coolant cap is a little sensitive when screwing it back on. You may be installing it incorrectly which does cause it to burp coolant when shut down. The threads are fine which may make it harder to screw on correctly. Once I reinstalled it the "burp" disappeared as I was instructed to by my friends Indy P-Car shop.

Just another thing to check out.

Hope it's that simple.

Lets hope ...

Thanks Jaak, but I hadn't touched the cap before the dump and had driven it 3000Kms in two days of hard driving just a couple of weeks before. If the bleed valve opens automatically how does the system retain pressure? Why did it suddenly decide to do it at high altitude?

Greg has a point.....
To be honest, this is the first time I have heard that the bleed valve lifts off its seat under normal driving conditions.....This valve vents to atmosphere, not to the coolant bottle.
Those of us who change our coolant without a vacuum pump drive for several heat cycles with the valve flipped open to release any air bubbles trapped in the system, but I assumed that the valve only opened to atmosphere when excessive pressure built up in the cooling system.
Perhaps some of our resident experts can comment....

the valve opens when it needs to. for me, it's always open at the end of a good drive.

check the coolant cap. they have been updated a few times (i think it's on revision #4 or #5 currently) because they let coolant out. other common areas are the coolant tank cracked (mine was) or the water pump weeping as it was failing (mine was). look around the hoses under the car near the coolant tank side tire for signs of coolant - mine was a crusty, dried crust...

and i know you said you never touched the cap prior to refilling, but it doesn't mean the PO didn't put it on wrong. they are very easy to put on crooked (i did) and lose coolant (i did) as a result. at 1500 miles a year, it's possible the car wasn't drive to the point that would cause a loose cap to cause dumping yet.

Thanks for the answers guys. It has the 04 cap at the moment, I'll check for an upgrade. The coolant tank is fine, I've had the carpets out and there is no sign of a leak and no coolant smell. I still don't understand how the system holds and pressure if the bleed valve opens on its own!
"and i know you said you never touched the cap prior to refilling, but it doesn't mean the PO didn't put it on wrong. they are very easy to put on crooked (i did) and lose coolant (i did) as a result. at 1500 miles a year, it's possible the car wasn't drive to the point that would cause a loose cap to cause dumping yet."
Possibly but the 3000Km thrashing I gave it a couple of weeks ago should of highlighted any faults I'd of thought.

Has anyone tried this, if so, what was your experience?

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