996 coolant bleeder valve question.

[phrenix]

Hi folks. A question regarding coolant bleeder valve.

I recently spent a load of money replacing clutch/flywheel and complete engine breather system. (Mentioning clutch/flywheel as this means engine was taken out).

OPC charged for coolant so guessing a degree of coolant topup took place when engine breather was replaced.
Went to drive car the other day & saw coolant reservoir was completely empty. Topped up with coolant and had car on ramp to inspect for coolant leakage. Thankfully none, so putting it down to air pockets working out of system and drawing coolant down into the depths!

I noticed the next day that the coolant bleeder valve was in open position, but coolant level was as it was when topped up. I closed the valve position and drove to work (about an hour journey). Checked to see that the coolant bleeder valve was in open position again.

Closed it again and by time I got home, had opened again. Any ideas why the valve keeps opening? My understanding is that it opens when pressure builds up too high?
Slightly concerned why this is happening.

[phrenix]

AN UPDATE..

I am still having the same issue with the bleeder valve popping up by the end of a drive.
Today I got the coolant system pressure tested in case the visual inspection had leaks that I did not see. The pressure was held so no leaks in the cooling system.

However, this still means that the pressure being built is higher than it should be. The friend who did the pressure test suggested that there may be a blockage somewhere. A Google on causes for high cooling system pressure bought up a few mentions of head gaskets!

I checked the coolant reservoir and the fluid looks quite brown (which was mentioned as a sign of head gasket issues). Would the pressure test hold pressure of this was the case?

[phrenix]

UPDATE ON THE UPDATE..

Took a closer look at the coolant. More rusty than the 'mocha milkshake' I read about re head gasket failure. Probably rust or dirt blown back out to the coolant reservoir as the high pressure bleeds out.

Also checked oil on dipstick to check for telltale marks of coolant getting into oil. Oil is clean as a whistle. No 'milky' appearance as should be expected with head gasket.

Could it simply be a blockage somewhere?

More info that makes me believe that it's not head gasket in that there are no over heating issues. Temp gauge reads as normal (just beyond the 80 mark) and fans kick in as normal as far as I can tell. Also no loss of coolant levels since topping up on the weekend.

Anybody have ANY idea what this could be?

[Martin & Kim 6853]

Not sure if it helps but I had a problem with the radiator cap which would occasionally pop the bleeder valve up, changed it and that problem went away, and like yours the temp was acceptable but I did have a leak (In fact i still do) so the levels did drop a bit.

Will be interested to hear what you discover good luck

[tr7v8]

Not sure if it helps but I had a problem with the radiator cap which would occasionally pop the bleeder valve up, changed it and that problem went away, and like yours the temp was acceptable but I did have a leak (In fact i still do) so the levels did drop a bit.

Will be interested to hear what you discover good luck

leak, Leak, LEAK LEAK after all that bloody work...........

[allanjenkins]

From what I understand the bleed valve allows coolant to bypass the thermostat, therefore allowing full system bleeding to take place from cold, when the thermostat would usually be closed.

The system still maintains pressure, the bleed doesn't actually bleed off pressure to atmosphere, its only a coolant bypass.

The downside would be slightly slower warm up than with the valve closed.

Think you should be considering a new cap.

From what I've read, for a complete coolant disassembly/assembly it takes 2 - 4 goes at top up to get the trapped air out of a system if it's not filled very slowly in the first place.

[Martin & Kim 6853]

Yes Jim developed a leak from the front offside somewhere am guessing it's a hose. Hopefully it's being looked at next week and the mans brief is to find the bloody leak, all I seem to have done for the last year is chase water leaks...

Annoying I know after the knuckle scrapping we did changing the rads