M50 Coolant Bleeding from Newbie

[mrtr10]

Good Evening guys

I would like firstly say Hi and congratulate you all on such a great website.

Now, I have been having problems bleeding the coolant system on my 520i SE Touring and would appreiciate any advice on how to get all of the air out of the system after new thermostat fitment.

Is there a knack to bleeding on this model?

Really appreciate any help or advice offered, so thanks in advance.

Kind regards
Mark

[DaveVoorhis]

Open the bleed screw on the rad. Fill the rad to the brim with coolant. Allow the level to drop until it stops dropping. Note that it drops slooowly. Refill to the brim. Repeat until the level stops dropping. Put the rad cap on. Turn the heater controls to full heat. Start the engine and immediately rev it to 3500 or so a couple of times, then stop it. Don't run it for more than 30 seconds. Refill the rad to the "cold" line. Do the start 'n' rev thing again, and verify that the level doesn't drop. Close the bleed screw and drive the car, keeping a close eye on the temp gauge.

[colo525i]

There are detailed instructions at bmwe34.net 2 things that helped me when replacing thermostat/bleeding. Did you put the thermostat in with the arrow pointing up? This should help the system bleed the air more quickly. Secondly, be patient and allow the air to bubble out of the system, it may take a while. I managed to drain the radiator, change the thermostat and put the coolant back in all while the engine was cold with no ill effects. Everything that came out went back in

[mrtr10]

There are detailed instructions at bmwe34.net 2 things that helped me when replacing thermostat/bleeding. Did you put the thermostat in with the arrow pointing up? This should help the system bleed the air more quickly. Secondly, be patient and allow the air to bubble out of the system, it may take a while. I managed to drain the radiator, change the thermostat and put the coolant back in all while the engine was cold with no ill effects. Everything that came out went back in

Thanks for the advice guys, have tried both of those methods and still seem to have problems even after all the bubbles seem to have stopped coming out of the bleed screw.

When driving the temp needle sits bang on the middle position, but, heater temperature flucturates from hot to completly cold as the revs rise and fall. After stopping and switching off engine, the rad cap was hissing and coolant being forced past. Very strangly the radiator was now completley cool, it had been hot whilst idling before going for a drive........

Any further ideas........please!!!

thanks again

[colo525i]

You might want to replace the rad cap, it should seal tightly under any condition. You should be able to bleed the cooling system almost entirely (if not all the way) while the engine/coolant are cold. The heater getting cold at idle is most likely a dead aux water pump. It sits up near the firewall and heater valves and they like to die with old age or coolant that is not changed frequently. Try the rad cap first if you've never replaced it.

[mrtr10]

good evening again guys,

Thank you for all of your advice and tips so far, have tried all of them but still have the following problem.

Car starts fine from cold and hot, engine warms correctly within 10-15mins and at idle and during normal road driving (around town and urban roads) temperature gauge sits bang on the centre mark of the dial. No problem there you say...... when checking coolant level after drive, I notice that the pressure in the system seems to be excessivly high and coolant leaking from expansion resevoir cap. Radiator is also only luke warm at best and bottom radiator hose which leads back to thermostat is completely cold.

If the car is driven at speed (60mph upwards) for a period of more than 10 mins, the temp gauge moves VERY quickly to the max and all of coolant is forced out of the expansion cap.

Work done so far;
1) Renewed thermostat
2) Bleed system - numerous times including using a pressure bleeder.
3) Renewed expansion resevoir cap
4) Flushed complete cooling system and radiator.
5) Confirmed no external leaks
6) Carried out block test, compression test, and cylinder leak test to confirm head gasket is not in trouble.

Water pump is under 3 months old (previous owner)

Strange thing is that, if you run the engine with no fan or viscous coupling attached, the cooling system appears to work correctly at urban speeds - as long as not in traffic. By 'works correctly' I mean that the radiator gets hot as does the lower hose. Obviously I have not tried this at constant higher speeds!!!!

Please, please, please, has any body got any other ideas???

Thanks for your patience in reading this long post, and for any ideas that you may have.

Kind regards, Mark

[632 Regal]

Mark, I still think you have an air pocket in there somewhere. Have you always had the heater on HOT and full when bleeding? Sometimes it's just a PITA to bleed. You also want to check the pisser line to see if it is clogged or not.

This is why I bought a V8

[mrtr10]

Good evening again guys,

could I ask a favour of any other member with a 520i with the M50 engine, I need to know the width and depth of the radiators fitted to your cars. Mine is a manual without A/C, so details on these models would be ideal.

I have a sneaking suspicion that the radiator in my car is too large for the model version. This would cause excessive cooling of the coolant and therefore closure of the thermostat from the return path from the radiator thus causing the 'engine side' of the thermostat to run hot.

Thanks again.

Mark

[cooljules]

Good evening again guys,

could I ask a favour of any other member with a 520i with the M50 engine, I need to know the width and depth of the radiators fitted to your cars. Mine is a manual without A/C, so details on these models would be ideal.

I have a sneaking suspicion that the radiator in my car is too large for the model version. This would cause excessive cooling of the coolant and therefore closure of the thermostat from the return path from the radiator thus causing the 'engine side' of the thermostat to run hot.

Thanks again.

Mark

Um sorry i cant help, i cant get into my destroyed susp car since the batt went flat and wont open with the keys...bllx

I know i had to bleed mine again again again...got it done in the end with the front end raised. I also have a 96 touring 525i now having both engine sizes, the power/torque diff is quite a big differance..i wouldnt go back to a 520i.

Selling the touring as i need to fund my new 525 salloon, but i will miss the space etc, did me well all over my E Europe trip last autumn.

[colo525i]

Mark, don't think you can have "too big" of a radiator, as the thermostat will open if it gets hot in the engine. I just realized both times i have had my car raised when bleeding it on the Driver's side (USA). It has worked just fine, bled cold after draining the rad and replacing the thermostat.