e34 bleeding/coolant troubles

[[1990]525]

Hi guys,

I'll preface this with by saying my car seems to have a portal to the 8th dimension where it's coolant goes. ~3/4 liter will disappear, yes disappear, in just a few miles of driving. It doesn't pool on the ground, it's not mixing with the oil, I put in a new head gasket and hoses etc, had the head checked at a machine shop and it was within tolerance, and this car runs like a champ.

Every time it would alert to low coolant I would refill it and began to notice that it seemed to have just barely emptied the expansion tank.

So I decided to do an experiment and ignore the low coolant warning light. I drove for ~3-4 weeks without refilling it all the while having low coolant light.

My car (1990 525) was overheating in traffic yesterday, so I gave in and picked up some coolant. Surprise, it had not gone down below the expansion tank and was 30 degrees cooler than the preceding days. Okay ignoring that the level is low maybe there is air trapped in the system which was causing trouble.

So I was going through the bleeding procedure but this happened: it would not bleed. I completely filled the expansion tank with coolant and even even had some backed up into the funnel but it would barely come up to the screw. So I screwed it back in, got up to normal temp. Left the radiator cap off and heater fully on during all of this. Opened the bleed screw, it would still not bleed. When I idled to about 1800 rpm it started to overflow from the bleed screw. When this became steady I reattached the screw and cap. Drove about 3 miles and when I lifted the hood again, the coolant was down to the last rib of the expansion tank.

So here are some questions:
a) wtf is my coolant going?
b) why did it take so much to overflow from the bleed screw?
c) what should I do if after refilling to cold mark again (once it cools down) it keeps sucking down coolant?

I'm at a loss!

Thanks

[genphreak]

Is it an M20B25, or an M50B25 engine in your car? The M50 is defaintely self-bleeding, probably the M20 will a bit too. On 2nd thoughts, you have a bleed screw, so definately you have an M20.

The most common problem for **gradual** cooolant loss however is invisible gaseuos expansion (BMW term this IGE (sorry, no I call this IGE) through weeping hose joints/plastic radiator parts- where a hose (more likely hoses) joins a connector or plastic tanks join the aluminium parts of the radiator- the seal becomes gradually lost due to deterioration/wear/calcification. There are a number of hoses to exercise your wallet on. The exercise will make you feel better, but it may not work: It could just be going around the head gasket into a cylinder. Check your plugs- a single cleaner one will be a tell-tale sign- though so will a failed oxygen sensor. Perhaps get the car on diagnostics to read the error codes?

All this assumes your is ***definately** not pissing out some place out of sight/uner the manifoild under heat and pressure...

[BennyM]

I've only ever been able to bleed my M50s by keeping the revs at 1500 to 2500 RPMs. It sounds to me like you've still got a lot of air in the system. And of course, if the level goes below the expansion tank, it'll start sucking more air in.

[Mordan]

this is how i bleed my M50 with no hassles

let the engine cool
open bleed plastic screw
fill radiator until bleed cries
put ignition on. You should hear some noise, like an electric motor
coolant is now gone
pour SLOWLY coolant into the radiator.
do it for like 5 minutes until bleed screw cries.
bring engine to température
you are done.
next day fill in if necessary

well I have done it only once so I'm not 100% sure my description is correct.

for coolant loss check the cabin heating radiator (PITA). Mine was leaking coolant. Easiest thing to do is to pressure test the system.

[bubba966]

Is it an M20B25, or an M50B25 engine in your car? The M50 is defaintely self-bleeding, probably the M20 will a bit too. On 2nd thoughts, you have a bleed screw, so definately you have an M20.

The M50 is NOT self-bleeding. Only self bleeding E34 engine is the M60 if I'm recalling correctly (one thing to love about my M60 besides the powerband...).

Many people have many problems bleeding the M50. I've never had a problem doing it, but I've always elevated the bleed screw by jacking up the front end or bleeding it on an incline.

[[1990]525]

It's an m20b25 and I'll check these things but all hoses were replaced and it's also been pressure tested and combustion gas tested.

Thanks :P

[M20Turbo]

I do as described below on my M20, works well......

http://www.bmwe34.net/E34main/Mainte...eplacement.htm
M20 Bleeding experience by moots:

Just to share a simple method to bleed the cooling system.I really cannot comprehend why we need to bleed,bleed and re-bleed the cooling system after every maintenence.I did this after replacing the thermostat and flushing the coolant:
(Mine's an m20 engine with the reservoir by the side of the rad)
1.Fill up the rad with the plastic bleeder screw(on reservoir) and metal bleeder screw(on t-stat housing),open.
2.When full,put a finger over the reservoir bleed hole and blow,yes,blow into the reservoir filler neck.(we are basically pressurising the system)
3.When water flows out of the t-stat housing bleed hole,tighten the screw.
4.Top up reservoir if required.
5.Now blow again until coolant exits the reservoir bleed hole and tighten when bubble free.
6.Top up coolant to the cold/kalt mark,tighten cap.You're done. No more bleeding required as all air is purged from the system. I have done this 4 times on three cars and it worked like a charm.

[edward]

My car uses coolant as well, since installing my 99 dollar ebay radiator. I noticed the other day that it was leaking where the coolant sensor plugs into the radiator at the bottom of the expansion tank.

Edward