Timm's BMW E31 Heater Valves and Auxiliary Water Pump Replacement
Including Replacing the famous 'Exploding Hose' on the V8's
 

If the BMW E31 has a weak spot, it's the cooling system. In particular, the heater valves get stuck or blocked, hoses explode, the auxiliary pump seizes up, leaks, and then the end drops off. This feature is shared with the E32 and E38, but one thing that isn't is the restorative heating, there's no 'REST' button in the E31 and the auxiliary water pump appears superfluous.

This 'How To' was instigated by the appearance of clouds of steam when pulling off the M5 into road-works on the A30. If there's one thing that makes you sweat, it's knowing you have only a few seconds to get to the side of the road before the head gaskets start complaining. In this case, the hose connection on the auxiliary pump failed:

BMW E31 840ci Sport Broken Auxiliary Pump

The plastic on the auxiliary pump gets brittle after a few years, the constant tugging from the coolant pipe that runs to the back of the engine eventually snaps off the connection. To get the car home I bypassed the auxiliary pump, this made absolutely no difference to the heater operation, so I will not be re-fitting it, but this is just a personal choice. The routine shows how to replace the complete heater system located behind the engine.

Right, start by removing the upper engine cover (10mm nuts under plastic covers) and acoustic material:

BMW E31 Heater Valves and Auxiliary Water Pump ReplacementBMW E31 Heater Valves and Auxiliary Water Pump ReplacementBMW E31 Heater Valves and Auxiliary Water Pump Replacement

Next, remove the microfilter housing, this can be removed without disassembly by parking the windscreen wipers in the centre of the screen and then removing the centre cone-shaped nut which is just in front of the passenger (RHD) wiper pivot. Now remove the two 7mm self-tapping screws each side of the housing:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Although the picture above shows the cover removed, there is no need to do this, also, partially remove the rubber seal shown just to the left of the socket wrench and the one above the microfilter housing. The complete housing can now be lifted upwards and slightly forwards and removed from the engine bay:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement
I took the chance to replace the torn seal at the bottom of the housing with self-adhesive foam

BMW E31 Heater Valves and Auxiliary Water Pump Replacement Blower Motor

Separate the connector pair in front of the heater valves and remove the housing:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Next, remove the cover over the heater valves, I have found the best way to do this is to use two large screwdrivers in a 'V' shape on each clip. Here's what the clips look like on the underside of the cover (as normal, one is broken):

BMW E31 Heater Valves and Auxiliary Water Pump Replacement Cover

And here is what the mating parts look like on top of the heater valves:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Next, remove the three  coned-nuts as seen above and shown below:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Often, the rubber body of the fixings fail, these are available from BMW:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Disconnect the loom to the heater valves (shown below) and the loom to the auxiliary pump (the bracket seen behind the valves normally holds the connector pair, but is missing in the picture below):

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

The heater valves complete with the auxiliary water pump can now be wiggled out to give better access:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Before removing the hoses, run water under the car to dilute any coolant that is lost, it is highly poisonous to animals and cats in particular are attracted to the sweet smell:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

The heater valves can be removed by fully loosening the jubilee clips and wiggling the pipes from the valves and the auxiliary pump. It is important not to put too much stress on the unions as they can break, or cause enough damage to fail when under pressure.

The same is true for the heater matrix connections, if the pipes don't pull off after fully loosening the Jubilee clip, slit the pipe along the length using a sharp knife. Although there is loads of room for removing the coolant pipes, some will face directions that a screwdriver can't get to - so use a ratchet and socket, here's one on the rear of the engine showing how awkward it can be:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Right, once all the coolant pipes have been removed and the heater valves have been removed from the engine bay, the new parts can be fitted. I have decided not to replace the auxiliary water pump, this is held on the heater valves by a single Torx screw:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

TESTING: With no power connected to the heater valves, they should both be open. Connecting the garden hose to connection number 1 (see below), water should come out of 2 and 3 with very little resistance. If there is any substantial back-pressure the valves need replacing. The valves have three electrical connections:
GREEN/YELLOW = 12V - Both Valves
YELLOW/BROWN = 0V - Right Valve
YELLOW/VIOLET = 0V - Left Valve
Connecting a 12V supply should fully close each valve - failure to do so requires the replacement of the assembly. There are replacement parts available, but quite often the coil itself fails, and this is not a separate item.

 The next pictures show the correct positions and the part numbers:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement
These two pipes (64218390607) run to the left and right sides of the heater matrix and rarely fail

BMW E31 Heater Valves and Auxiliary Water Pump Replacement
This short pipe (64218391897b) is one of two that can fail spectacularly, the 'b' shows it has been updated

BMW E31 Heater Valves and Auxiliary Water Pump ReplacementBMW E31 Heater Valves and Auxiliary Water Pump Replacement
The long pipe (64218367782b) can also be fatigued by the movement of the engine and tear at the unions

Note that the pipe designations above assume the auxiliary water pump is not fitted, where it is fitted, pipe 1 connects to the end of the pump, and a short pipe (64211383407) connects between position 1 on the heater valves and the side connection on the auxiliary pump. Below is a diagram with hose numbers for the complete system:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

Start replacement of the heater pipes with 64218391897b which is the short pipe that runs from the back of the engine to the left-hand heater-matrix connection, then the two heater-matrix supply pipes 64218390607 that run from the heater valves. Note that the ETK shows one of the pipes as 64218390608, however, both types are identical, they are also now supplied as 'b' versions. Finally replace the long pipe (64218367782b) that runs from the rear of the engine to the auxiliary pump or connection 1 on the heater valves if the pump is not replaced.

As I am not replacing the pump, I have fitted the auxiliary pump electrical connector to the bracket to stop it flopping about:

BMW E31 Heater Valves and Auxiliary Water Pump Replacement

NOTE ON BLEEDING: The standard bleeding procedure as shown here is not sufficient when all the heater pipes have no coolant in them. At stage 4, the engine needs to be revved to around 4000RPM to get the coolant circulating. With the heater set to 32C, check that heat is available from the vents once the temperature gauge is in the centre. Rev the engine again if there is no heat - sometimes it takes a few goes to get the coolant circulating the heater matrix.

All done, time for a cup of tea.


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