Water Pump Replacement

January 18, 2003

Reading time ~7 minutes

Symptoms

  • loss of coolant
  • evidence of water spray in a circle around the fan - check the bonnet lining and sides of the radiator hoses
  • dampness on the front of the engine underneath the fan (after the car has been sat for a few hours)

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You will need

  • a replacement water pump - try Euro Car Parts.
  • a 32mm spanner for the viscous coupling on the fan
  • a mallet to hit the 32mm spanner with (really!)
  • some antifreeze and deionized water, to refill the system
  • your normal collection of spanners and sockets
  • a “Stanley” knife blade
  • some 800 grade (medium/fine) wet & dry paper
  • gasket sealant if required
  • 2 hose clips

Procedure

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Remove the fan

Stand at the left hand side of the engine and put your 32mm spanner on the viscous coupling bolt. Hit the top of the spanner towards you with the mallet (it is a reverse thread). If you are lucky, the bolt will turn and it will be easy to unscrew. If (like me) you are unlucky, you will have to use a bit more cunning. You can buy a special BMW tool to hold the pulley still while you turn the nut, or you can jam it in some way. This is what I did. With the spanner in position ready, I jammed a socket wrench against the belt, thereby applying tension. I also had the end of the socket touching the small cooling fan on the front of the alternator, stopping it turning. One good blow to the spanner with the mallet in my free hand was enough to get the bolt turning. Remove the fan and store it propped up in the same orientation as it was in the car. I don’t know why you have to do that, but I read it somewhere else. I presume the viscosity changes if you lie it horizontally.

Remove the pulley

Loosen the four pulley bolts. Now loosen the belt tensioning bolt on the alternator. Rotate the front adjuster nut clockwise to crank the alternator further into the engine and therefore loosen the belt. Now go back to the fan pulley and fully remove the four bolts, then remove the pulley. Let the belt hang in place.

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Remove the engine hoist bracket

The next obstacle to pump removal is a hoisting bracket on the front of the engine. It has two bolts with different sized heads. One is visible, so remove it first. Feeling around the bracket with your fingers, you should be able to locate the other one. Remove the second bolt and bracket.

Hose clips

Slacken off the two hose clips and move them to the centre of the small hose. Don’t remove the hose yet.

Pump

There are six bolts around the pump. The ones at the bottom are easier to locate by touch. When you start to slacken off the last bolt, coolant will start to seep out from behind the pump. When the bolts are all out, pull away the pump and remove it from the short hose. Coolant will flood out of the front of the engine. Remove the short hose.

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The old pump

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Prepare for the new pump

You will need to remove the remains of the old gasket from the front of the engine before you replace the pump. Leaning over the engine, and with the aid of a torch, carefully scrape away as much as possible of the old gasket, using a Stanley knife blade. When you have done that, go over the gasket area with some wet and dry to finish off.

Attach new pump

Put the gasket on the new pump - it is easier to fit if you stick it there with some gasket sealant. If you are happy to line up the pump and get the bolts through the holes in the gasket dry, then go for it. The gasket will still do its job, with or without sealant. Attach the pump to the engine. I’ve no idea what torque the bolts require - just don’t go mad or you might strip a thread.

Attach engine hoist bracket

Re-attach the engine hoist bracket you took off earlier. Start with the top (larger) bolt, it makes it easier to line up the bottom bolt (the one which is harder to see). You should be able to put the bottom one in by touch.

Attach hose

Find the small hose that you took off earlier and thread two new hose clips onto it. Attach it to the same place it came off and tighten the clips. Beware of the one on the pump end - you don’t want it to foul the pulley which you are about to re-attach. Look at the “before” picture to see how to fit it.

Attach pulley

Put the pulley back on the front of the new pump and bolt it into place with the four bolts. Hang the belt around it, and crank the aduster on the alternator to tension the bolts. Now tighten the tensioner itself to stop it moving. Give the four pulley bolts another tweak when you are done.

Attach fan

Line up the bolt on the back of the viscous coupling and rotate the whole fan until the threads bite. Remember it is a reverse thread. Once it has started you can spin the fan to tighten it fully. Give it a quick tweak with the 32mm spanner but don’t worry about it too much, the normal rotation of the fan will tighten it.

Add replacement coolant

Check the specs in the manual - mine recommends a 40% antifreeze mix. I made it more like 50%, figuring that the previous owner must have been topping it up for a while due to the leak, thereby diluting it more.

The first header tank full just sat there, until I pumped the large top radiator hose with my hands. There was then a sucking noise from the header tank, and all the fluid in there drained off. It took about 3 more tanks full before the level remained steady. There is a small bleed screw on the thermostat housing at the front of the engine - if you loosen it, coolant is supposed to flow out. It didn’t seem to do much good on my car - coolant flowed out even when the system had obvious airlocks.

Perhaps it is only useful when the system has been completely drained.

Start the engine

Fire her up (leave the header tank cap off for now). What you should find is a small stream of water flowing into the neck of the header tank filling hole, via the small pipe on the left of the car. Go and give the top hose a few more squeezes to make sure, and loosen the bleed screw again to make sure you’ve still got coolant flowing out and not air. Another quick way to remove airlocks is to disconnect the small pipe which goes from the radiator to the header tank. If you pull it off at the radiator end you should get quite a bit of air out before water starts squirting out.

Err on the side of caution

That’s the end of the job, so you can now tidy up and go and make yourself a nice cup of tea. However, just in case, I’m going to carry a few litres of ready mixed coolant with me for the next few days, and I’m keeping my eye on the coolant level to make sure it isn’t going down.

Thanks

Thanks to my good friend Rob Knott, an ex-BMW mechanic who gave me the detailed repair procedure as we walked around Stonehenge. Thanks to his tuition I was able to undertake the work myself. Unfortunately he now works for that other German marque.

Caveats

The pump cost me £25, and I spent about £50 at Halfords on the coolant, spanner, hose clips, wet & dry paper, gasket sealant etc. etc. I also had to take the day off work. Although I got the satisfaction of doing it all myself, in hindsight it would have been cheaper to get my local independant BMW garage to do it. I was quoted £50 parts and £50 labour, which now seems very cheap.

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