Bleeding the E34 Cooling system

[vping]

How are the cooling systems to bleed? I heard that it is a pain in the ass.

[genphreak]

Not at all. If the system pressurises, you'll be ok. If it doesn't you have no hope.

Depends on the model- M20 and M30 you have to bleed manually. All the later engines autobleed, so long as you follow the correct procedure. Most importantly you have to use the factory coolant, or Prestone, or a very few special others. Using any other 'compatible' coolant will end Burn Your Wallet later....

[shogun]

m30 bleeding page_2 (http://www.nmia.com/~dgnrg/page_19.htm)

[ScottyWM]

Vince, I must have bleed my M50TU a dozen times over the years given all the water pumps and radiators I've replaced (yes I used BMW coolant). Never had a lick of trouble bleeding. Park it with the nose pointing uphill, follow the procedure, no muss no fuss...

[vping]

Thanks guys.

My daughter blew a heater hose and had to get it taken to a local shop. $300 for the hose. Wanted to then charge me another $400 for the other hoses and the thermostat. I'll fess up and say I should have replaced all the hoses when I got it but I assumed the prior owner did because he kept such great care. Live and learn. I'll take care of the other hoses and thermo myself when she comes home.

Something good came out of it though. I might have found another. A1997 528i. I'll hear more about it in a few hours and will let ya know.

Cheers,
Vince

[John in CT]

300 bucks, now that's a New York price alright,

Sheeesh,

John

[vping]

Hey Scotty,

When you have a moment, contact me via email.

vping at optonline dot net

[Victor]

Scotty,

I wonder if you'd mind clarifying a points regarding bleeding air from the M50TU please. What do you mean by "if the system pressurizes?" Also, the "procedure" involves filling the expansion tank until coolant overflows from the bleeder. But after that drops, there may still be trapped air, so I'm bleeding again and again after drives without the full expansion tank and getting bubbles. What's going on here ...

Thanks,
Vic

[Rustam]

I bleed it simply (m30 engine) :

1- let the engine work, it will heat beyond the middle notch. I let the needle touch the red.
2 - stop the engine and turn the bleed screw. Some coolant will come out and steam.
3 - let the engine cool
4 - check level and refill
5 - repeat the cycle till overheating stops.

By third cycle the system is usually blead. Simple and effective.

[Victor]

Wow. I'd be reluctant to see my (M50TU) engine get that hot. I've never seen it past the halfway point. And especially if there are air pockets, I'd fear warping the head.

Bentley's procedure is characteristically scant, leaving much to the imagination...

[genphreak]

I bleed it simply (m30 engine) :

1- let the engine work, it will heat beyond the middle notch. I let the needle touch the red.
2 - stop the engine and turn the bleed screw. Some coolant will come out and steam.
3 - let the engine cool
4 - check level and refill
5 - repeat the cycle till overheating stops.

By third cycle the system is usually bled. Simple and effective.

Definitely those steps work.

For the uninitiated, M50 and M60 engines aren't so finickity- and the bleeder screw is incorporated into the top of the radiator. The car auto bleeds to a much larger extent, so you usually only have to bleed once and top off a few times.

As much as the M20, M30 and M70 are harder than others, I don't like this approach as I worry it might stress the head gasket (due to the sudden opening of the thermostat). The level of coolant in the head is low/non-existent, so letting it heat to that point before letting the air out in one go risks changing its temperature too fast. The M30 is a long engine and the head gasket probably its second weakest design attribute. It is the other attributes that we love...

Here is the procedure I use:
0. Make sure the car is level- as the coolant level begins low, should the engine not be level there will be some coolant in one half of the head, and none in the other, as the engine warms. This will stress the gasket more when the thermostat opens and coolant flows through, quenching the heat from the upper half.
1. If changing the thermostat, consider drill a small (2mm or 1/8") hole in the top of the thermostat's flat 'mounting disc'. This allows air to escape promptly when you fill- coolant thus floods the head prior to the thermostat opening. Bill R told us about this mechanic's trick some time back, but beware using it on cars used in cold conditions. The bigger the hole the more coolant can pass the thermostat when it is closed. The hole allows a miniscule amount of coolant to bypass. It should not affect operation in >10 degrees C. Below that it will reduce engine temperature very slightly by allowing perhaps a cup of of cold coolant through the engine every few minutes, allowing the engine to run cooler, wear more and when it is really cold, use more fuel.
2. Open the bleeder screw.
3. Fill with coolant, until some escapes from the bleeder screw. If you have not drilled a hole in the thermostat, you won't see coolant escape until the coolant from the radiator (rather than the head) floods the water neck
4. Start the engine and keep topping off for a few minutes as the engine warms.
5. Close the bleeder screw
5. Grab a bottle of coolant and go drive the car to heat the engine. Stop every few blocks to open the bleeder and top off the coolant.
6. If you have a hole in the thermostat, you only have to do this once and not much air will escape before clear, non-bubbly coolant escapes the bleeder
7. If you DON'T have a hole, the a large amount of air will escape after the thermostat eventually opens. At this point, the coolant level drops dramatically and you should top off with a perhaps 1/2 to 1L of coolant. Because the cold coolant you add gradually dribbles into the radiator from the coolant reservoir, it is warmed after mixing in the radiator before entering the engine. Also, you may need to check a couple of times after the thermostat opens- as it opens and closes a few times during warm up. Air bubbles sometimes exist in other pockets in the head and can take some time to make it to the water neck where we can remove using the the bleeder screw.

Note: Once the engine is at a stable temperature you should stop bleeding, just do quick checks to see if there are bubbles in the water neck. If the engine has large amounts of heat in it, de-pressurising the system can allow coolant to boil and push coolant out of the bleeder.

Also, a note to novices:

1. Beware boiling coolant under pressure- it burns faster than anything else you can imagine
2. The bleeder screw on these engines can corrode if the engine has not had the correct coolant or it's been not been changed regularly enough. There are 2 issues with it:
- the screw can seize due to electrolysis in the thread. usually they crack open ok but you need to use a good hex socket to avoid slips under pressure.
- the screw has a little pin deep down at the bottom of the screw's sealing face that slips into a small hole in the top of the bleeder's orifice. It can shear off due to corrosion/fouling. If it does, coolant will flood out less neatly. If you have an M30, it might be worth having spare bleeder screw as they are really a wear item.

[632 Regal]

For the uninitiated, M50 and M60 engines aren't so finickity- and the bleeder screw is incorporated into the top of the radiator. The car auto bleeds to a much larger extent, so you usually only have to bleed once and top off a few times.

As much as the M20, M30 and M70 are harder than others

I have personal experience with the M60 and M70. There is no bleed procedure which is why I like them. They self bleed, no screw to temp to the red zone (would freak me out). Not sure as no experience but my first sense says not a good idea. AU might be different?

As for 6 cylinders I am still learning as I hope to scoop a few of the failed bleed cars up for cheap. Close to Atlanta GA and there are a ton of failed bleed victims. New radiators, water pumps, gaskets etc. Fix em flip em.

[Rustam]

It would take a period of time within the red and likely a run under load, not just idle to damage the head or gasket. Most certainly nothing will occur if the needle just touches the red while idling. I even wait a few moments to let the needle go into red, to insure good steam.

Done this with FelPro and Victor Heinz gaskets many times.

[genphreak]

I have personal experience with the M60 and M70. There is no bleed procedure which is why I like them. They self bleed, no screw to temp to the red zone (would freak me out). Not sure as no experience but my first sense says not a good idea. AU might be different?

As for 6 cylinders I am still learning as I hope to scoop a few of the failed bleed cars up for cheap. Close to Atlanta GA and there are a ton of failed bleed victims. New radiators, water pumps, gaskets etc. Fix em flip em. Ooops- My bad- M60 and M70 self bleed. No bleed screw in the raadiator like the M50 or water neck like M20 and M30.