Timm's E63 and E64 Auxiliary Water Pump Replacement
Is your cabin heater fizzling out when idling - no REST function?
All the big BMW’s with mechanical main water pumps are fitted with an auxiliary water pump - these are used to provide two functions -
they increase the flow of coolant around the cabin heater when the engine is idling, and they also keeps the coolant flowing when the
engine is switched OFF so that the cabin can be kept warm (know as restorative heating and activated by pressing the REST button).
Just like the earlier models (E31, E32, E38 etc), the auxiliary water pump fizzles - but this is much more of a
problem on the N62 engines as these idle at 550 RPM whereas the M62 trundles around at 700 RPM - and the
coolant circulates fine at those revs.
The auxiliary pump is fitted on the LHS of the engine bay, underneath the air filter assembly - access is
straightforward and this job is relatively easy to do with a minimum of tools. The pump is fitted to the
chassis via a rubber mount and this does not need to be replaced, just the pump assembly - the pumps are
available on-line with and without the rubber part. I used Part Number 64116988960 as a search term on
Ebay and found a whole bunch, mine was £55.
The pump can be tested quite easily, switch the ignition ON (key in, press the START button when NOT pressing the brake pedal), set the
temperature controls to the highest setting and the fan speed to low - this will enable the pump independent to the coolant temperature.
In a quiet environment you should be able to hear the pump running under the air filter assembly. If you can’t hear it, push a dowel onto
the pump from above (it can be seen under the filter) and put the other end to your ear - if it is running you will be able to hear it.
Enough waffle, let’s get the dud pump out and a new one in. Start by removing the main air filter assembly as shown below:
The connections to the pump are two quick-release hoses and a single electrical connector on the lower end. We will be disconnecting the
hoses and there will be a certain amount of coolant-loss. We have a number of choices, we can slurp out the contents of the expansion tank
with a fluid pump, that will help a bit, or we can drain the coolant system via the drain-cock at the bottom of the radiator:
It’s out!
Grease the connections on the new pump, this will ensure a leak-free connection
Fit the electrical connection to the underside of the pump, un-thread the lower hose from the vacuum pipe and with the pump above the
rubber mount refit the hose
Stick your thumb over the central connection and push the pump into the rubber housing and immediately refit the upper hose - it’s in!
Refit the vacuum pipe back in the clip and then refit the air intake assembly. There will have inevitably been a certain amount of coolant loss
so we need to replace this using BMW’s coolant:
And that’s about it, check the coolant level the next morning when the engine is cold and refill if necessary. It should take slightly longer to
read this than it does to actually do the job!
All done, time for a cup of tea
The downside with this method is that you will still have coolant loss and you also have to do a major coolant-bleed to get the air out - instead,
I’m going in without draining any coolant (as usual)! Well worth saying is that coolant is poisonous to animals, especially cats who seem to
love to slurp the stuff up. Where there is a chance of coolant escaping I stick the garden hose under the car so that any escaping coolant is
immediately diluted and carried away.
So, in we go then, as soon as a coolant pipe is removed the coolant will start to flow out and the way to stop it is to raise the pipe - the long
coolant pipe that runs towards the back is restricted by the vacuum pipe shown below, so unclip it ready so that you can thread the long pipe
past it:
Below are the two quick-release fittings for the coolant hoses. These have wire clips that stop the hoses popping off and these
need to be pulled evenly so that both sides leave the lower position and click into the upper position as shown in the two
pictures. Although these are quick-release they take a bit of manipulation to release them.
There is a trick to releasing the minimum of coolant - and it goes like this:
Release the top pipe first, and as soon as it pops off, bend it upwards to stop coolant flow
Lift the pump in the rubber housing (it is just pushed into place) - this reduces the coolant loss from the top connection
Disconnect the lower hose, manipulate it under the vacuum hose and prop it upwards to stop the coolant flow
Lift the pump upwards and disconnect the electrical connection from underneath
Switch the ignition ON (key in, press the START button when NOT pressing the brake pedal), set the temperature controls to the highest
setting and the fan speed to low - this will enable the pump independent to the coolant temperature. Start adding coolant, the auxiliary
pump should be circulating the coolant through the heater matrix and it should appear at the neck of the tank in a small stream as seen
below. There will be a few puffs of air as well as it self-bleeds.
If the heater matrix has any air in it this can be released once the expansion tank is correctly filled so that the float meets the top of the
neck (as seen below) - start the engine and allow to warm for a minute or so, then give the throttle a poke so that the revs reach 3000 RPM
- this will push any air out of the system.
