overheating and having trouble bleeding system

[nomansland92]

My 1988 325ix has been having lots of over heating problems lately so here the story. As long as I'm drive and doesn't have to be real fast ill be fine but if I'm stopped or letting the car warm up it will overheat. the p/o replaced the fan clutch so i don't think its that but its a possibility. and i've replaced the w/p and thermostat also so that's not the problem. But i can't get it to bleed the air pocket out. ill let it warm up and heater on and on a hill and when i crack the bleeder air comes out and some fluid but tons and tons of air and it just keeps coming till it starts want to over heat so i shut it off and it does the same thing but as im bleeding it, the fluid in the over fill tank never goes down at all not even a drop unless i shut the car down and open the cap then it sucks it down. but then just more air out of the bleeder screw. so i was thinking maybe its the reservoir tank cap but the over fill works and anti-freeze comes out from the corner of the fender. If i feel the bottom left corner of the rad(driver side) its barely warm when the top is hot like it should so possibly plugged but that would make it not bleed and it never leaks. its like its pulling air in some where. Kinda makes me think the head gasket but its coolant and oil are not mixing and I'm not blowing white smoke.
Any help or suggestions would be really nice because winters coming and i have to get the 944 in storage and off the road soon.
thanks so much, Stevan

[stumble_t]

where is the coolant going?
pressure test your system and find the leak.

[nomansland92]

ill get a pressure tester and ill give it a shoot. So ill let you know
thanks for the input though

[Kershaw]

i think your idea of air coming in at some point is valid. you might have a leak somewhere.

[jlevie]

The cause of this is a leaking head gasket. The head will have to be removed, checked for warp and most likely surfaced.

[nomansland92]

i did a pressure test and its not leaking at all, and with no white smoke and i have good compression and no fluid mix and there's no vapor on any plugs, all those signs make me think its not blown but it would make sense if it was but that's like the last thing on the list to replace. But thanks everyone so far ill keep you posted on what i find out in off to the parts to for rad cap and thermostat and all those goodies
Thanks, Stevan

[jlevie]

A small head gasket leak can exist that only leaks air into the cooling system. The only symptoms of that may be random overheats (usually only low speed), an inexplicable loss of coolant, and/or air from the cooling system on successive bleeds.

The simple DIY test for this is to fully bleed the cooling system, drive the car for just a bit (but don't allow it to run hot), and re-bleed. Release of a significant amount of air then or on a subsequent bleed is evidence of a head gasket failure. You can also try a chemical test for combustion gasses in the coolant, though I've seen false positives and false negatives with that test.

The definitive test for a small head gasket leak is to pressurize each cylinder with 180psi for several minutes while monitoring cooling system pressure with a sensitive gage. A rise in cooling system pressure on one or more cylinders is evidence of a leaking gasket. A negative result on a cold engine requires that the test be repeated on a hot engine.

[nomansland92]

ok ill do another compression test and ill leave it sit for awhile and see if it bleeds into the coolant

[jlevie]

A compression test won't tell you anything, but a high pressure variant of a leak down test that I described above will.

But I will say that your description of what is happening tells me the head gasket has failed.

[Ceeker]

My 1988 325ix has been having lots of over heating problems lately so here the story. As long as I'm drive and doesn't have to be real fast ill be fine but if I'm stopped or letting the car warm up it will overheat. the p/o replaced the fan clutch so i don't think its that but its a possibility. and i've replaced the w/p and thermostat also so that's not the problem. But i can't get it to bleed the air pocket out. ill let it warm up and heater on and on a hill and when i crack the bleeder air comes out and some fluid but tons and tons of air and it just keeps coming till it starts want to over heat so i shut it off and it does the same thing but as im bleeding it, the fluid in the over fill tank never goes down at all not even a drop unless i shut the car down and open the cap then it sucks it down. but then just more air out of the bleeder screw. so i was thinking maybe its the reservoir tank cap but the over fill works and anti-freeze comes out from the corner of the fender. If i feel the bottom left corner of the rad(driver side) its barely warm when the top is hot like it should so possibly plugged but that would make it not bleed and it never leaks. its like its pulling air in some where. Kinda makes me think the head gasket but its coolant and oil are not mixing and I'm not blowing white smoke.
Any help or suggestions would be really nice because winters coming and i have to get the 944 in storage and off the road soon.
thanks so much, Stevan

I had the same problem; fill the reservoir; wait for it to go down. Then start the car, put the heat on full on defrost. You might have air in the back of the system. You have to make sure all the channels are open for coolant to flow. Wait for car to get to opp temp. Crack the bleeder open and rev engine from the throttle body to get the pressure up and air out. run it like this until you see bubbling. Close it and recheck temp inside car. If the reservoir need topping up do so. Just make sure you replace the cap otherwise back pressure will push it out inside of sucking it back into the system. you may have to do this a few times even if the car gets to 3/4 hot. as long as not in the red for to long you're ok. Head warpage typically happens while in the red for prolonged period and worse when under load-driving. Let the motor cool down and then take it for a spin to see what happens. Again you may have to do this a few times for it to stabilize.

[nomansland92]

ok i think i got everything figured out and all good now. So i've pretty much been having this problem since i did the timing, water pump, and thermostat, heres what im thing happened. I found out today that the clutch fan is junk and same for the new thermostat so that explains heating while stopped and i think all the air was from the coolant stating to boil and create steam and that's what all the air was so i got a new thermostat and bled it again and a little air then straight fluid and while driving it runs a little under half and when stopped for like a few minutes it will heat up because the fan doesn't engage but unlike before it would start jumping up almost as soon as i stopped. Ive never let it hit the red so i'm hoping the head gasket doesn't blow. I don't mind doing the work to replace it but i don't really half and extra 100 bucks for everything right now.
I hope this was every thing but won't know till i get a new fan clutch.
Thanks everyone,