how to bleed an m50?

[munky30]

Whats the process? I have a friend thats a bit of a numpty and they want me to bleed their e36 325... whats the process/where are its nipples?

[munky30]

anyone?!

[Ant]

fill system through expansion tank on rad, open the bleed screw on top of the rad with a coin or wide/big flat tip 'driver( warning, they are shite and break ! )

top up till coolant runs from bleed screw hole, leave the rad cap OFF for now.

run engine to temp, heater on as normal.

Top up as required, check for heater etc etc

run the engine to 2.2K rpms in neutral, then watch the pump pull the coolant from the tank, then whack the cap back on whilst maitaining the fast "idle"

test drive, allow to cool for a few hours and top up the exp tank as required.

NB: if the rad and all pipes/heater are hot, and the coolant wont"pull" then I'd suspect a failed plastic impellor on the W/pump, all M50/52 are blighted with te wrongness.

HTH, works for me- everytime

[munky30]

Cheers ant... turns out its not as simple as we thought.

We did pretty much what you said to bleed it. It worked at first, water was coming out, thermostat had opened as both rad pipes were hot.

But no heat, the hoses to the heater matrix werent hot.

And nothing but air was coming out of the bleed valve.

So I guessed it was an airlock... 15 minutes later, still just steam coming out of the valve... one hell of an airlock!

Another 5 or so minutes and it was still just air. No heat inside the car etc, it wasnt overheating though.

My guess is that the pump's gone as you say... there was a rattle/vibration kind of noise coming from it when we revved it...

Its a 'new' (couple of months old) water pump though,,, but a pattern part.

Its an e36 320 if thats any use)

[DanThe]

Could be the heater valve, also a common fault

[Dan318-is]

Bleeding is notoriously c*ntish on BMWs though, i had a nightmare with mine in the middle of chiswick once, was there for an hour and a half until we got all the air out; make sure all the rad all hoses are boiling before you start changing water pumps etc; if they are not hot then its not bled!

[munky30]

Both hoses were hot, the rad was bloody hot evenly all over... so hot I have a burn from it... The hoses to the heater matrix weren't hot... a tad warm, but nothing compared to the rad ones.

We ran it for a good half hour with the valve open and there was nothing but air coming out.

The car was parked on a slight incline, front upwards.....

[Dan318-is]

The heater matrix pipes should also be boiling, they are the ones tha ti have found always are the last to give.

[munky30]

so is it more likely to be the heater valve... as no water is getting to the heater?

[Dan318-is]

Im not an expert by any means but it just sounds like you still have an airlock around the heatervalve area, believe me i no how long you have probably been bleeding it but its not always enough!

[munky30]

Ok, will give it a bit longer tomorrow and see what happens.. It wasnt overheating while we were doing it so we could have gone on longer... just got bored

There was a definite rattly noise from the pump though when it was revved.

[fozzymandeus]

I wouldnt immediately blame the water pump. It would take a seriously poor pattern part to still have a plastic impeller these days as genuine BMW replaced the design in about 1997. Also, wouldnt the car have cooked itself long before now if there was no pump?

You have to wait quite a while for the thermostat to open... is there any warmth in the hose to the bottom of the rad?

BMWs are a pain to bleed because there are no bleed screws!

[Ant]

Its important to realise there are 100's of plastic pumps still on the shelves and you WILL be supplied one unless you specify otherwise....

My dealers( all 4) will fob anyone off with the old stock unless you're clued up.

THey have no choice I suppose, they cant just be binned, although they should

[fozzymandeus]

Its important to realise there are 100's of plastic pumps still on the shelves and you WILL be supplied one unless you specify otherwise....

My dealers( all 4) will fob anyone off with the old stock unless you're clued up.

THey have no choice I suppose, they cant just be binned, although they should

Very good call. Hadn't occurred to me how long the part might have been sitting in a warehouse for. Yuck!!

[munky30]

Its a pattern part, no idea if it's plastic or not...

Thermostat works fine, both hoses to the rad got hot. And it does have a bleed screw

[fozzymandeus]

munky, there'll be a bleed screw to drain the system but plenty of other cars have bleed screws all over the place to check for air locks... but in a BMW you have to run the engine for ages to pump the system clean.

[Andyboy]

Could also be a shagged heater valve, very common. To get my bastard to bleed, I bypassed the heater valve by running the heater valve supply pipe straight to the matrix after which the system bled quickly. Removing the stat and drilling a tiny hole (2mm is plenty) in the outer rings helps too.

[Andyboy]

I wouldnt immediately blame the water pump. It would take a seriously poor pattern part to still have a plastic impeller these days as genuine BMW replaced the design in about 1997

Not so. The M54 built at least as late as 2001 still has a plastic impeller pump. I stripped a 2000 728i engine with such an item, original 2000 date stamp.

[fozzymandeus]

Ah hell. Just me being too trusting I guess.

[munky30]

Right, water pump was taken out and taken to bmw, they said its fine (and its metal).

Heater valve next... might advise bypassing it as you say andy... what are the good/bad points of doing that?

[munky30]

and how do I do it?

[Andyboy]

Easy. Look at the heater valve - one pipe in, one pipe out. Disconnect the pipe from the back of the head to the valve at the valve itself, it's on the bulkhead. Disconnect the pipe from the valve to the matrix at the matrix itself. Fit the pipe from the head to the matrix. It means the heater will be permanently on but you can shut it off with the sliders and have the cold air vents on. The rubber seal in the valve breaks up and blocks it, seriously restricting flow, making it impossible to bleed the cooling system after a drain down.

[Demlotcrew]

That rattly noise could be a worn Vanos unit.

Ha i bet BMW must have laughed at you asking them if a water pump is worn or not.

[DanThe]

Plenty of BMW engines do not have steel impeller water pumps, not plastic either, they call it a 'composite material' and is supposed to be better than both