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E34 (1989 - 1995)

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Old 10-28-2013, 12:18 AM
Mamij Mamij is offline
Location: Denmark
Join Date: Apr 2007
Posts: 598
Mein Auto: BMW 320i M52 1996
Why its generally EASY PEASY to bleed a BMW

Roberto was right all along. See this thread for full exhaustive details :


To quote just ONE passage :

" air cannot get trapped in the block as the area behind the thermostat is directly connected through an open passage to the upper radiator hose. the main exit for the coolant flow passes behind the thermostat and into the upper radiator hose passage with no restriction whatsoever. The air cant get trapped back there it will escape into the radiator(past the thermostat cover bleed screw on its way "

The engine in the car is installed at a slight incline to the horizontal as well, which, together with natural coolant flow while the engine is running, moves air out of the block to the radiator, where it accumulates under the bleed screw, ready to be vented easily.

Those people with M20 engines do not have a thermostat housing with 2 ORIFICES, one for the thermostat and one that opens to the cylinder head directly....which is the case with the M50. That's probably why BMW put 2 bleeds screws on the m20 engine, to help them out better, and why they changed this inconvenient design for the subsequent engines.

I hope this puts paid to the MYTH that forums sometimes propagate, which, in this case, is that it is difficult, problematic, complicated etc to bleed an engine. Jack up the front of the car, turn cartwheels, and whatnot. It is not. Its the easiest thing in the world.

If you are overheating, and you feel that bleeding actually fixed the overheating, you

a. have observed incorrectly.
b. were either very short of coolant, or your system was clogged because it had not been flushed for years and years and in the course of fixing your overheating, you ended up flushing the blockages out,
c. there is something else wrong with your system (likely thermostat and/or wp), it is a transient failure, and you just happened to get lucky for now. It will happen again down the line.

I recall some people getting mighty offended when Roberto pointed out that this should be a simple thing and if you are struggling with it, something else must be wrong with your system or you must be doing something wrong without realising it (and you didn't realise what you later did right either).

Facts triumph loud proponents of superstition, usually advanced by older folks who genuinely struggled with this in cars of a bygone era that had poorer cooling system designs. These people refuse to think critically because they lack the fundamental self confidence to admit they could be wrong. They hold back truly inexperienced people - who can't yet tell the difference - bigtime.

I will close by quoting from the bfcer referenced above.

" BMW has chosen to remove the thermostat from the airlock-prone top hose position and place it in the airlock-free bottom hose position. A very wise move, for even while filling a completely dry block, all the air is guaranteed to come out the top radiator hose and be released via the expansion tank or bleeder screw. "

Another forum myth bites the dust !

Last edited by Mamij; 10-28-2013 at 08:00 AM.
Old 10-28-2013, 02:13 AM
M540FELLA's Avatar
M540FELLA M540FELLA is offline
Location: Chatt,TN
Join Date: May 2012
Posts: 831
Mein Auto: 95 540i m sport
Re: Why its generally EASY PEASY to bleed a BMW

You mean you were right? Come on man seriously....:sly:
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