Question : Please help out a desperate BMW tech, 99 Grand AM

[90turbo1]

Wow this site has it all, anyway.....

i am a bmw tech and found my self working on a 99 grand am 3.4 SFI that was a trade in at dealership. the car had a coolant flush performed to it and after that it started to leak coolant from the intake manifold (lower) onto the transmission area. we then took the intake upper and lower off and found rear bank gasket on coolant port to be distorted and full of stop leak.

i cleaned best i could installed new gaskets and reinstalled the lower and upper intake manifolds. Yes I put the push rods back in correct order and torqued the rocker arms correctly.

motor runs perfectly and i bled the cooling system using the bleeder on front bank of motor the best I could.

now after about 10 min the coolant will start coming out of the over flow tube next to rad cap on over flow tank.

we suspected a bad cap so got a new cap and now it takes longer to do this but still comes out over flow tank. i have bled and bled system there are no bubbles in over flow tank and temp guage gets to about 200 and goes no higher. fans come on as normal and everything is great untill the cap is put back on motor.

engine is not leaking and all coolant lines appear to be in correct location.

any help on this.... i know someone has to have done this repair before so maybee they have had the same experience.

thanks

[robertisaar]

if its not overheating, i don't see the issue... maybe theres just too much coolant in the radiator, so its purging it into the overflow tank...

does it get sucked back in by the radiator as it cools?

[90turbo1]

well there will be considerably less when the motor cools in the over flow tank. but when cold I fill it to the line that says cold.

it will continue to push coolant out of over flow tank till the motor is shut off. or cap is removed.

doesnt seem right to me.

[robertisaar]

it almost sounds like it *generating* water... the only other thing i can think of is that the coolant might not be flowing right, making a big ass steam pocket...

but if the guage is right, its not gonna make steam at 200, hell it takes 212 at atmospheric pressure to boil plain water.

[90turbo1]

well like I said its not really boiling, just being pushed out over flow as if the cap is bad, but I ahve tried a new cap and tested the new one and it holds 15 lbs like it should.

i am just wondering if there is air trapped in the motor some where, the v12 BMW's will kinda do this if not bled properly. is there a specific procedure to bleed this motor...??

[robertisaar]

is there a specific procedure to bleed this motor...??

here's what alldata has to say about it:

[90turbo1]

well followed that. the system has been flushed so there is no more dex cool in system.. I understand that running green collant isnt the best but as long as they are not mixed it should be ok, not for long run.

its just odd what this thing is doing.

[robertisaar]

well followed that. the system has been flushed so there is no more dex cool in system.. I understand that running green collant isnt the best but as long as they are not mixed it should be ok, not for long run.

its just odd what this thing is doing.

you can mix the green stuff and dex-cool, but it only lasts as long as the green stuff is rated for.

i'm thinking since you did find a large chunk of stop-leak, i'm thinking it might be to blame for this issue(or at least point to what is causing it).

[90turbo1]

yeah I wll flush system again tomorrow.

[robertisaar]

yeah I wll flush system again tomorrow.

i'm willing to bet theres something in there messing with the flow(like a chunk of stop-leak lodged somewhere it shouldn't be) that was caused by either the owner being cheap or by their mechanic for being lazy...

[90turbo1]

yeah agreed?

well i will keep posted.

[robertisaar]

i just thought of something:

i don't think its likely, especially since you're NOT seeing any air come out, but possibility of headgaskets gone/going bad? and the compression is pushing the coolant out of the radiator? this problem you're dealing with now might have already happened, and the stop leak might have been to fix headgaskets...

[black05gt]

Hmm, my first thought was a blown head gasket, but was also wondering if a bad thermostat, stuck in the closed position, would also force coolant back into the overflow tank. But you state that it's not overheating, so I'd have to go with bad head gasket pressurizing the cooling system.

[95Grand-Am]

I have had this happen on a malibu with a 3100. I ended up changing the coolant tank because I couldn't get the cap to seal. Is yours building proper pressure or is i pukeing before presure is reached?

[90turbo1]

well here is what I found so far.....

let car sit over night with coolant in it. topped up to proper cold fill line and started. temp reaches 200 or so and then will start to push coolant out over flow tank hose.

so I was checking a few things and the two small hoses going to the top of the tank were not flowing. removed them and reved the motor and nothing. finally a glop of stop leak came oozing out of the small hose from the radiator to the expansion tank. so I flushed the system again and filled with just water this time (hell coolant is getting expensive) same thing but this time its a bit different. now over flow tank will stay normal till the motor is reved and when you let off the throttle the coolant will start to come out of that hose again next to the cap. but if you increase revs again it stops. I can almost control it by using the throttle.

so I checked the temp about 200 to 210. with cap on over flow tank there is no pressure in the hoses. I mean usually when a car is at operating temp the hoses are hard with pressure. this are is not. it feels like there is no pressure iin the system but the water pump is working as should.

its baffling me, i know now that there is no air in system. we did a block check and there were no combustion gasses coming up through the over flow tank.

i am leading towards a plugged up radiator (that seems to be where the stop leak accumulated lately) and a t-stat but I am unsure.

so what is the flow pattern of the cooling sytem to and from that bottle.

since there is no pressure in the large hoses when hot, could the t-stat be shut. (although the car doesnt appear to over heat by guage ect.)

or is the over flow tank leaking some how and not allowing pressure to build. I am un famaliar with this "open" type of cooling system.

thanks for all help and I am trying everythign suggested.