Coolant bleeding problems on an M20...

[G-Bear]

It’s a 325i. I changed the timing belt, water pump and various other bits. All went well until putting new coolant in. I worked on it at the start of the week, then had to go away with work so shall try my best to recall what I did.

The block was completely drained. The car was sat level. I followed the instructions from the E30 Bible, from what I remember it went as follows:

I removed the top hose completely that goes from the thermostat to the top of the radiator and took the hose out from the thermostat end that goes down to the bottom of the radiator (the one with the steel hose that runs diagonally down across between the rad and engine).

I kept the ignition off but turned the blowers to on (full) and the temp dial to hot.

I then slowly poured a litre of coolant in from the expansion tank.

Then slowly another litre into the hose that goes to the bottom of the radiator.

And then another in the expansion tank and so forth alternating between the hose and the expansion tank all a litre at a time.

I think after about the third litre that went in from the hose to the bottom of the rad, it was brimming out the top of the hose, so I reattached the hose to the thermostat. I put the rest in though the expansion tank only.

Once all 5 litres of coolant was in I then started putting de-ionised water in. Probably (from what I can remember) I got about a litre or so in then coolant started to come out from the top of the thermostat. So I put the hose back on that goes from the thermostat to the top of the radiator. Then put the ignition on only so that the blowers where blowing (turned to hot). And continued to fill from the expansion tank until that was full.

I then put the cap back on the tank and started the engine, keeping the blowers on on hot.

The engine got up to normal temperature after about ten minutes or so but the blowers inside the car where staying cold.

I’m sure from what I remember the top hose going into the radiator was hot, but the hose coming out the bottom was cold. I’m not 100% sure; it may have been the other way. But definitely one was hot and one was cold.

I switched the engine off and opened the bleed valve on top of the thermostat housing and coolant came out straight away.
The engine only took about 7 litres in total.

The only other thing I’m not 100% about was if the battery was connected from the start or only when I switched on the ignition, I’m sure that wouldn’t make much difference but thought I would include it just in case.

Sorry for being vague in areas I worked on it until midnight last Tuesday then was up at 5am the next day to go away on a job and have only just managed to get in front of a computer. I followed what was written in Andy's book I just donb't have it here with me currently to check.

I found this thread from doing a search, could I adapt to this?

http://www.e30zone.net/modules.php?name ... ng+coolant


Also On another note; The timing belt that was on previously was sat right at the front of the pulleys (closest to the fan) and had a couple of chunks taken from it, you could see where it had been rubbing against the inside of the upper metal cover. Do the belts have a tendency of moving? Or was this just shoddy work of the person that fitted it, there wasn’t a spring present on the belt tensioner so I figured whoever fitted the last wasn’t that caring about things. Or is it a sign of something else I need to address”¦

Any help I would be grateful of... cheers.

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[HJG-E30]

I had some bleeding troubles with my M20. In the end, I parked on a steep hill (front facing upwards), took the engine round to 6000 RPM and opened the bleed screw. This got the air out pretty damn quickly. Ran absolutely spot on from then

[maggspower]

I had some bleeding troubles with my M20. In the end, I parked on a steep hill (front facing upwards), took the engine round to 6000 RPM and opened the bleed screw. This got the air out pretty damn quickly. Ran absolutely spot on from then

This, apart from the 6000rpm thing no need to go that mad. 2500 will do it

Jacking the front up will help but a steep hill is better, one of the few advantages of living in Wales

[G-Bear]

Thanks gents.. This is what I was going to try next. I'll drive the front up onto some ramps.. would have forgot about putting the revs up though... Thanks again..

[Andyboy]

It sounds like the timing belt was fitted by a craftsman.

M20's are 99.999% of the time very easy to bleed. With the ignition off the heater valve reverts to a default open setting....assuming the heater valve isn't knackered. Is the car trying to boil and pressurise the top hose?
Have you put a new stat in? If you have, it might be faulty. These days I just drill a tiny hole in the stat outer ring - 2mm is plenty big enough. It makes no difference to the running temp but it makes filling and bleeding the system easier. Before doing that, I'd disconnect the upper water hose at the bulkhead. If no coolant comes out, continue adding water until it does. On many E36 six cylinders with A/C it's often the only way to get the bastards to bleed up.

[G-Bear]

I hadn't changed the thermostat. The top hose into the rad did seem pressurised. I'll check the hose going into bulkhead. Not that I have a total knowing of the journey the coolant takes around my engine I figured that might be where the trapped air would be. Thanks Andy..

[bmw9818]

i was having issues bleeding mine, car on a flat surface, didnt drill any holes using the normal stat bleed nipple, was trying for 2-3hours, went to get some lunch my dad did it when he came in the garage for a fag in like 10 minutes! still dont know how he did that!

[aimlessrock]

i had similar problems bleeding my M20 and eventually my mechanic sorted it by using a vacuum bleeder...took him minutes apparently.

[maxfield]

i had similar problems bleeding my M20 and eventually my mechanic sorted it by using a vacuum bleeder...took him minutes apparently.

Absolutely awesome tool! Saves so much time.

[G-Bear]

Got it sorted today.

I disconnected the top hose at the bulkhead. There was no coolant there. Once I undid the cap on the header tank it must have let the air through as coolant started coming through where I had open the system up at the bulkhead.

So I connected it back up and drove it up onto ramps and left it running to heat up, running the revs at 2.5k every so often. Heat was already starting to come out of the blowers. I bled it from the thermostat valve whilst topping it up from the header tank as I went.

It helped that I looked up in the bently manual the course that the coolant takes around the engine rather than just filling it up blindly following instructions

Everything is spot on now. Thanks all for your help and comments..