Shared Knowledge
"BMW Z3 - How to Replace the Water Pump"
31 January 2013
Summary: make sure the water pump needs replacing and not the thermostat housing or thermostat or some other coolant component. Water pump replacement is definitely a do-it-yourself (DIY) job.
Background:
1997 Z3, 58,000 miles.
Water pump never replaced.
Temperature gauge climbed above mid-gauge and headed towards max and steam coming from under hood.
Steam was coming from center of car or water pump area.
In my case, steam indicated a coolant leak (hose, thermostat housing, water pump, radiator?) but if car overheating and no leak or steam, water pump impellor could be bad.
The water pump in the Z3 is fairly small (image above) and mounts directly into the engine block. In my case, the original water pump had a metal impellor but apparently some pumps had a plastic impellor that could break off causing no water to be pumped and thus car overheating.
If your Z3 is overheating and you can not see a coolant leak, might or might not be water pump but rather a stuck thermostat or several other possibilities. Do not replace a part until you know or are fairly confident the part is actually bad.
Finally note that there are many good sites on the Internet that give instructions on replacing the water pump. Consult several before beginning a replacement.
Tools and parts needed:
32millimeter (mm) thin wrench. Available from bicycle stores.
Ratchet, sockets, wrenches. 10, 11 mm
Screwdrivers: flat blade and probably Phillips.
Antifreeze leak, drip, catch, container. Only needs to be 4 or 5 inches tall but should be at least 1 foot or more length and width. I used a plastic storage container I bought for $8, Staples.
Antifreeze. 2 gallons. Use BMW if you want. I use premixed 50-50 Prestone.
Good work light.
Flash light or other focused light source.
Hand cleaner, towels.
Perhaps latex gloves to keep antifreeze off hands.
Tube of white lithium grease
Since you have to remove the AC and serpentine belts, why not replace them now??
Since you working on coolant, why not replace the upper and lower radiator hoses??
Does the pump need replacement??
Set park brake: well, tight.
Jack up car on passenger side front. Jack up enough to get your drip, leak, catch, container under middle of car, water pump area.
Move your antifreeze catch container under the middle of the car, right under the crank shaft. Orient such that the long side is parallel with front of car, potentially catching most of the antifreeze that may leak, drip.
Note: if you a mind to, you could place some sort of material under the front of the car to keep antifreeze off your garage floor.
Note: antifreeze will burn, so no open flames anywhere.
Car coolant completely cool, cold.
Remove water pump fan. Use 32mm thin wrench on water pump fan nut. As fan threaded opposite of normal, you must move wrench to right to loosen nut. As water pump may try to turn as you move wrench, may have to place a thin, long, flat blade screwdriver between 2 water pump pulley bolts hold water pump pulley as you turn think wrench.
Once water pump fan loose, hand unthread it from shaft, not allowing it to drop once it completely free of shaft.
Lean fan on radiator for now.
Remove air filter box. You do this by unclipping the mass air flow sensor (MAF) and the 2 bolts holding the box to the chassis. You then pull back and up to get box out of car.
Move fan out of fan shroud by moving it towards the opening you created when air filter box removed. Set fan aside out of car.
Making sure there is antifreeze in reservoir,
Check car that there are no tools anywhere and there is nothing obstructing or could fall into pulleys or belts.
Start up car.
Check under car for leaking, dripping, antifreeze.
If leaking, move to driver's side fender and looking towards the passenger side with a focused light beam try to determine source of leak. Hose leaking? Leaking around water pump? If leak is clearly from water pump, shut down engine and jump to instructions on replacing water pump.
If no leak, check temperature gauge and if car not overheating, let it continue to run.
As coolant in system eventually gets hot enough, thermostat will open.
Once again check under the car for leaks and then back to driver's side and check area under thermostat housing.
The Z3 comes with a plastic thermostat housing that can suddenly crack and leak coolant but only does so after thermostat opens.
If you can see coolant leaking out of thermostat housing, you need to replace the thermostat housing, click here.
Replacing the water pump:
With fan completely out of the fan shroud, undo the 2 plastic rivets holding the fan shroud to the radiator. These are more-or-less one time use, so pop them out using a flat blade screwdriver. I used small cable ties when I wanted to reattach fan shroud.
Loosen the clamp on the small hose on the driver's side of the radiator, pull hose off radiator.
Loosen and remove the upper radiator hose. Loosen the thermostat housing end first as coolant will leak out when you pull the hose off.
With upper radiator hose removed, lift up on the fan shroud and then move it out of the way by laying it across the driver's side fender.
Using a 10 millimeter (mm) socket or wrench, crack the 4 water pump pulley bolts. If you crack them loose now, easier to remove once you have the serpentine belt off the pump pulley. Crack means just to loose a little and not remove.
Now go under the car on the passenger side and find the air conditioner belt. It is the outer belt on the crankshaft.
The 1997 Z3 uses the old style belt tensioners that use a large coiled spring to make the tension roller tight. In my case, I was able to pull the belt by hand enough to work it off the pulley on the AC unit. Remove belt.
Go to driver's side and find serpentine belt. Grab it with your hands and pull and see how the tensioner works. In my case, again, I was able to hand pull the belt enough to remove it off one of the pulleys. Remove belt completely.
Remove pulley on water pump shaft.
Using a socket and ratchet, remove the 4 bolts holding the water pump to the block.
With all 4 bolts removed, pump may not simply pull out but might need some persuasion via a rubber hammer striking down on shaft. Do not use a flat blade screw driver in the flange between the pump and the block.
When you ready, pull pump straight out of block and there will be a gush of antifreeze, hopefully into the container you placed below.
Now since you have the bucket and are working on the front end, I suggest you replace the upper and lower radiator hoses. They do not cost much but if they spring a leak out on the road somewhere, hassle time. If you do replace hoses, make sure you position you bucket under the area when you pull off a hose.
Take a clean cloth or paper towel and wipe out inside of hole in block.
Take new water pump and apply white lithium grease to the rubber gasket and to the pump mounting flange.
Place new pump back into block using the picture below. You want the large round ?? on the front of the pump to be at the bottom when you place the pump into the block hole.
Hand insert and tighten the 4 water pump bolts.
Once you are sure you have all 4 pump bolts properly seated, use a ratchet and socket to tighten pump to block. Apparently 10 foot pounds of torque is all that is required. As I do not have a torque wrench that will set 10 foot-pounds, I hand tightened, tight.
Put the pulley back on the water pump shaft. I had trouble doing this at first as hard to align holes in pulley with holes in pump shaft face but once I got the first one, the others were easy enough. Because pump turns freely, not going to be able to fully tighten pulley bolts at this time but tight by hand the best you can.
To see how to replace belts, click here.
With belts back on pulley's tighten the water pump pulley bolts.
Move fan shroud back into place. Note that the shroud has some plastic tabs that slide into plastic tabs on the radiator, so you need to align these tabs as you slide the shroud down onto the radiator. Once you are sure all shroud tabs are engaged, take cable ties and secure the shroud to the radiator on the left and right side.
Take water pump fan and move back into fan shroud.
Place fan onto water pump shaft and turn fan nut to the left or passenger side to begin to tighten the fan onto the shaft. Once you have it threaded on, use the 32mm thin wrench to tighten the nut. If needed, place a thin, long, flat blade screw driver between 2 of the water pump pulley bolts to keep the water pump from turning.
Reconnect the small hose coming out of the fan shroud to the radiator on the driver's side.
Reconnect the upper and lower radiator hoses.
Remount the air filter box. Take box and move it down at an angle into front of car and then down onto chassis. Reconnect the MAP and bolt to chassis.
Check over your work. No tools laying anywhere that could fall into belts or the fan?? All appears correct??
Fill coolant reservoir,
On radiator top, passenger side is a small plastic screw. Use a screw driver to remove this screw. This is the air bleed hole for the coolant system.
Open garage door, if not already open.
Start car and watch coolant reservoir. Add coolant as required to keep reservoir filled between the cold and the hot marks on the tank.
Check under car for leaks. You should not have any.
Let car warm up, checking gauge and level of coolant in reservoir.
Do not gun car accelerator as coolant will probably shoot out of air bleed hole in top of radiator.
As car warms up, eventually the thermostat will open allowing coolant in the block to circulate through the radiator.
Continue to check under the car for leaks. When the thermostat opens, if there is a crack in the thermostat housing, you will begin to see coolant leaking below your car.
If no leaks, let car continue to heat up watching the reservoir level and for air bubbles in the radiator air bleed hole.
When all air is out of the system, coolant will begin to overflow the radiator air bleed hole and it is time to put the plastic screw back into the hole and tighten it down.
Once again, check coolant level in reservoir and keep it at the full hot mark.
Remove catch container from under car.
Let car down off jack.
If you still have a leak:
Ok, you replaced the pump and you still have a leak, what to do??
Must clearly identify the source of the leak. Pump could be leaking around flange where it mates with block and if so, might have to remove pump and apply a gasket sealant to flange.
Leak might still be from thermostat housing, either via crack in housing or where it bolts to engine.
In any case, shut down car and walk away for a day or so. Know it is frustrating to go through a multi-step replacement only to find it did not fully fix the problem. I have had to take a component in and out several times before I got problem fully solved. Take faith, you can do it, just might take a little more time and effort than you initially planned on.