E31 M60/M62 Cooling System - Flushing - Filling - Bleeding - Venting
This routine shows the easy way to drain, flush, re-fill and vent the cooling system including the heater core
My new (to me) 840ci had an unknown quantity of anti-freeze in the cooling system, and that, combined with the strange blockage I had in the heater core convinced me that the coolant needed to be replaced and the system flushed. The cooling system on the V8's have a bad reputation for being difficult to bleed, but if you follow this routine you should have success first time.
Note: Anti-freeze is poisonous to animals, in particular, cats are attracted to the sweet smell. It is difficult to catch all the coolant while flushing, so keep a stream of fresh water running under the car to dilute and remove the coolant.
First of all we will remove the coolant into a container. To get the most coolant out possible, reverse the car up a pair of ramps. Without the car tipped forward, only 3 Litres will come out (out of 12 Litres). The easiest way to extract the coolant is to remove the lower hose. If the original hose-clamp is fitted, note which way around it is fitted, it has a sprung section that keeps a constant pressure on the hose, the sprung side must face the radiator - I found the easiest way to remove it was with a socket and ratchet.
Before removing the hose
clamp, it is best to remove the hose that feeds the heater matrix as this will
be needed for the flush. To get access to the correct hose, disconnect the
heater valve connection and remove the securing plate:
Loosen the clamp and remove this hose (just a few drops of coolant will come out):
Place a container under the lower hose and completely loosen the hose clamp, the radiator boss is serrated so wiggle the hose from the radiator carefully. Once the coolant flow has stopped, remove the container, it's time to flush the system. It is quite easy to flush the system using the hose that was removed from the water valves.
This hose runs directly to the heater matrix - then to the water valves - through to the rear cooling pipe - through the engine and the pipes in the engine 'V' - streams them mix at the water pump and then enter the radiator at the top-hose, through the radiator and out the lower hose.
A standard Hozelock nozzle fits nicely in the hose:
Fire up the hose and keep going until the water runs clear from the lower hose connection:
With the water still running, poke the lower-hose back on the radiator and this will back-flush the expansion bottle:
Once the water is running clear, remove the nozzle from the heater hose, disconnect the radiator lower hose and wait for the remaining water to leave the system. That's the flushing done! Roll the car off the ramps, refit the lower radiator hose and the heater hose. Refit the connector bracket and re-connect the heater-valves electrical connector. For the refill, use only BMW coolant and distilled (or de-ionised) water:
The cooling system holds 12 litres or so, so you will need 6 litres of the BMW anti-freeze. All well in theory, in practice there will be a few litres of water still hanging around the cooling system - for this reason, start refilling with neat coolant - it is quite possible that there is still 5 or 6 litres still in the system.
A funnel that fits securely in the expansion tank helps with the filling:
Remove the vent-screw, grease the o-ring (silcone grease or Vaseline), refit fully and then undo by two turns:
Refill using the neat coolant until you have used all 6 litres - and then move on to the distilled/de-ionised water - the chances are that you are not going to get much in there! Fill the expansion bottle right to the top, refit the expansion cap and give the top-hose a good squashing to get the air out - remove the cap and then add more water. Once no more air can be ejected refit the cap but leave the vent screw loose. Now drive the car onto ramps or roll it down the kerb:
Leave the ignition in position II (ignition ON), set the drivers heater temperature to 32C (past the detent) and fan on the slowest speed - this will run the auxiliary pump and circulate the coolant through the engine block.
Loosen the bleed-screw two turns
Pour the coolant into the expansion tank, if the coolant reaches the neck of the bottle fit the cap and tighten the bleed-screw, squeeze the top hose a few times, remove the cap and loosen the bleed-screw
Squeeze the top hose a few times, at this point the coolant should be circulating via the auxiliary pump and coolant should be seen entering the expansion bottle from the small-bore pipe into the neck of the expansion bottle. If the coolant is not circulating, squeeze the top-hose and while squashed fill the expansion tank right up to the brim, release the top-hose. Repeat until the coolant circulates.
Refit the cap, tighten the bleed-screw and start the engine,
loosen the vent-screw at regular intervals to release any air:
Allow the engine to reach operating temperature while ensuring the engine temperature does not go past the centre line on the instrument cluster gauge. Only top up the fluid by a small amount if this happens, stop the engine when re-filling.
Once the engine has reached operating temperature, switch the engine off and check for any leaks. Only attempt to get the coolant level exactly right when the engine is fully cool (at least 8-hours).
Time for a cup of tea!