DIY parts & procedures for replacing e92 M3 belts, tensioners, and water pump

Just did the job last week. Here are the parts and procedures for the job.

Parts needed for the job:

https://www.ecstuning.com/b-genuine-bmw-motorsport-parts/water-pump-e9x-m3-with-upgraded-aluminum-impeller/11518331044~oeb/
Genuine BMW Motorsport water pump with aluminum propeller
11-51-8-331-044
(OEM BMW water pump with plastic propeller which is a little cheaper has different part number)


BMW water pump screws with washers (x4). M6x25-U1
07129905558


https://www.ecstuning.com/b-genuine-bmw-parts/coolant-bleeder-screw-priced-each/11537793373/
BMW plastic coolant bleeder screw with o-ring
11-53-7-793-373


https://www.getbmwparts.com/oem-parts/bmw-pulley-11517838676
Water pump pulley

https://www.getbmwparts.com/oem-parts/bmw-strut-bolt-07119905525
Water pump pulley bolt x4

https://www.getbmwparts.com/oem-parts/bmw-belt-tensioner-11287835417
Alternator belt tensioner

https://www.getbmwparts.com/oem-parts/bmw-tension-strut-11287841546
AC belt tensioner

https://www.getbmwparts.com/oem-parts/bmw-serpentine-belt-11287837898
Alternator belt

https://www.getbmwparts.com/oem-parts/bmw-ac-belt-11287841529
DOUBLE SIDED AC belt (IMPORTANT: check and see if your M3 has single sided or double sided AC belt!!!!!)

https://www.getbmwparts.com/oem-parts/bmw-idler-pulley-11287841531
Idler pulley with the bolt in the middle (IMPORTANT: double check to see if your M3 uses idler pulley with the bolt in the center or with the bolt off center as the earlier built ones are equipped with idler pulley with a bolt located off the center)

https://www.getbmwparts.com/oem-parts/bmw-cap-11287535867
Idler cap

https://www.getbmwparts.com/oem-parts/bmw-cap-11287835996
Tensioner cap (need 2)

https://www.getbmwparts.com/oem-parts/bmw-belt-tensioner-11287841527
AC belt tensioner pulley

https://www.getbmwparts.com/oem-parts/bmw-tension-pulley-11287838194
Alternator belt tensioner pulley


AC belt pulley bolt
M8x100-8.8
07 11 9 905 696

Tensioner bolt (need total of 4)
11 28 7 839 136
M8X32-ZNS3


Alternator belt pulley bolt
07 11 9 905 855
M8X60-ZNNIV SI


1 gallon/bottle of OEM BMW coolant



Procedures for replacing M3 belts, tensioners, and water pump:

I cannot tell exactly how long it took me to do the entire job. I believe it took me about 6 to 8 hours. No need to jack the car up for this job for me.

You may want to label all the bolts as you remove them so you can have a reference of what bolts are for which parts when you install the new parts.

Remove air filter box

Remove front air duct box (has 2 screws at the front)

Covers the air intake and the oxygen sensor duct with cling wrap and secure with tape

Loosen up the hoses in the plastic hose holders on the bottom of the fan before start removing the fan. It’s important to do that otherwise they may keep pulling down the fan when you try to pull the fan up.

Disconnect the plug to the fan on the left hand side

Remove one screw on the left securing the fan.

Move away the tubes on top of the fan

Start taking out the fan. Take your time and be careful. It’s quite a struggle to remove the fan.

After removing the fan, loosen the AC belt tensioner to loosen up the AC belt. Use the 14 mm 2 ended wrench and use the circular, tilted end. Turn the wrench clockwise to loosen up the tensioner.

You have to (it’s a MUST!!!) remove the idler pulley first before you can take out the AC belt.

Loosen up the alternator belt tensioner and loosen up the alternator belt and remove the belt

Remove the AC tensioner screws to remove the tensioner and the pulley connected to it.

Before removing the alternator tensioner, you MUST MUST remove the water pump pulley first to give room to remove the alternator tensioner screw on the left.

Remove the water pump pulley.

Remove the alternator belt tensioner and the pulley attached to it.

Put towels or a low profile big pan under the car as the coolant will be pouring down.

Use a trash bag and duck tape it to around the water pump to reduce the coolant mess.

Remove the four bolts holding the water pump.

Screw in 2 of the bolts into 1 hole on each side in the middle. This will help to loosen up and help to push out the water pump. Get ready for the mess from the coolant fluid.

Put the new water pump in place. It will not be all the way in until you screw in the 4 bolts. As you tighten up the 4 bolts, the water pump will get push in.

Now it’s time to put on the new tensioners.

First you have to attach the tensioner to the AC belt pulley and attach the tensioner to the alternator belt pulley. IMPORTANT: pay attention to the side and direction of the tensioner being attached to the pulley. Note that the tensioners have marking “top” on one side.

Put on the alternator belt tensioner and the pulley.

Put on the new water pump pulley.

Put on the AC belt tensioner.

Put on alternator belt. Make sure you double check on the way the belt loops around the pulleys. If you loop it in a wrong way, the pulleys will turn in the wrong directions and it will cause damage to the parts. It’s easier to put the belt onto the small pulley on the alternator last after loosen up the alternator tensioner.

Now it’s time to put the AC belt and the idler pulley on. My M3 has double sided AC belt.
Please make sure you double check if your M3 has single sided or double sided AC belt as the way you loop around the pulleys is DIFFERENT. Then make sure you double check on the way the belt loops around the pulleys. If you loop it in a wrong way the pulleys will turn in the wrong directions and it will cause damage to the parts.

Next, put the double sided AC belt (you may have a single sided AC belt if your M3 was made in ?4/2008 and before so make sure you double check before buying and install the AC belt as the way you loop the AC belt around the pulleys WILL BE DIFFERENT) in place for the idler pulley before putting on the idler pulley. It’s IMPORTANT to have the belt in place for the idler pulley first because with the idler in place first, there’s not enough room for the belt to pass through to seat it on top of the idler pulley. If you have a single sided AC belt, I believe the belt actually goes on to the bottom of the idler pulley so you do not put the belt on top of the idler pulley but double check first.

After that, it’s time to put on the AC belt. It’s easier to position the belt onto the power steering pulley last when you loosen the tensioner to give rooms for you to position the belt into the power steering pulley.

Now put on the small plastic covers or caps for the AC belt tensioner, alternator belt tensioner, and idler pulley.

REMEMBER to put those covers/caps on before putting the fan back in place. Otherwise, you have to remove the fan again in order to put those plastic covers on. It happened to me last time so remember and it’s apain to remove the fan.

After putting those covers on, it’s time to put the fan back in place.

After the fan is back in place, secure the 2 hoses to the bottom of the fan to the plastic holders on the bottom of the fan. I couldn’t reach the holder on the left bottom of the fan but as long as you can secure the 2 hoses to the plastic holders on the middle and right bottom of the fan that seem to be secure enough to keep the hoses in place.

Put the tubes on top of the fan back in place.

Reconnect the plug to the fan.

Put the screw back onto the fan on the left hand side.

Now it’s time to refill the coolant.

Remove the coolant reservoir cap.

Loosen the bleeder screw. You do not need to remove the bleeder screw. Only loosen it is enough. If you have the OEM plastic screw, make sure you turn it slowly and carefully as you do not want to break it otherwise you have to figure out how to get the broken plastic bleeder screw out. You make want to replace the bleeder screw with a new one actually as plastics degrade over time especially being exposed to heat next to the engine. I replaced mine with an aftermarket titanium bleeder screw.

Mix coolant with distilled water in 1:1 ratio. For me it required less than 1.5 gallon coolant mixture so 1 gallon of BMW coolant purchased was more than enough.

Slowly add coolant to the reservoir to 3/4 between minimum and full marks. Fill up to the max mark (top of the second ball mark). You will hear some bubbling sounds in the reservoir tank which is normal as it vents.

After refilling the coolant reservoir tank and the bubbling sound in the reservoir has stopped, leave the coolant reservoir cap open and close the bleeder screw (if you leave the bleeder screw open, the coolant will sip out of it during the next step).

Now start the M3 and turn the heat to max but leave the fan setting to low.

Run the car for 15 minutes to warm up the car. Leave the reservoir cap open the entire time. Once in a while, loosen and close the bleeder screw (once again, slowly and be careful if you have a plastic bleeder screw) as it may help to vent but get some paper towels ready as coolant will come out from there when you loosen the bleeder screw.

Turn off the car. Check the coolant level and refill to about the max level mark if needed and it’s done. If the coolant level is a little more than max, it’s ok as long as it’s not a whole lot over the max as the level will likely be lower by the next day as the cooling system continues to vent and the air continues to be removed from the cooling system.

Close the reservoir cap and secure the bleeder screw and you are done. Congratulations!!

Daily for the next few days, check the coolant level again (while the engine is cool), as it may show the level lowered to between minimum and max level mark. This is normal. Just add more coolant to the max level. If the level is higher than max, then you have to remove some from the reservoir tank. You can use something like a a syringe connect with a rubber tubing so it can reach into the reservoir tank and suck out whatever amount of excess coolant.

Hope that helps.

Thanks for the detailed write-up and part numbers!

Update. After a few weeks have gone by since the job was done, the car still runs well and the coolant level remains the same without signs of leakage.

suprafrank wrote

Update. After a few weeks have gone by since the job was done, the car still runs well and the coolant level remains the same without signs of leakage.

Great write-up, thanks very much.

I'm looking at this DIY for preventative reasons. My coolant is original so I think needs changing soon and I've read that thermostats are worth replacing at this sort of age too (I think it's working fine but for a few£££ worth a change). I think the A/C, power steering belt and the alternator, water pump belts could probably do with a refresh for age reasons too.

Does my reasoning seem ok?

Has anyone got experience of the lifetimes of water pumps or tensioners (I'm trying not to waste money)?

My M3 is Nov 2012, 38k miles

Thanks

Harryc9 wrote

suprafrank wrote

Update. After a few weeks have gone by since the job was done, the car still runs well and the coolant level remains the same without signs of leakage.

Great write-up, thanks very much.

I'm looking at this DIY for preventative reasons. My coolant is original so I think needs changing soon and I've read that thermostats are worth replacing at this sort of age too (I think it's working fine but for a few£££ worth a change). I think the A/C, power steering belt and the alternator, water pump belts could probably do with a refresh for age reasons too.

Does my reasoning seem ok?

Has anyone got experience of the lifetimes of water pumps or tensioners (I'm trying not to waste money)?

My M3 is Nov 2012, 38k miles

Thanks

My '08 has 66,xxx miles.
I'm still on the original water pump and thermostat.
Both belt tensioners are also the originals, but I did have to replace the pulley wheels themselves at around 55,xxx miles.
When I saw the price of the complete tensioner assembly that BMW wants you to purchase, I decided that I'd try and find the wheels themselves. That saved some significant money.

Davisca455 wrote

My '08 has 66,xxx miles.
I'm still on the original water pump and thermostat.
Both belt tensioners are also the originals, but I did have to replace the pulley wheels themselves at around 55,xxx miles.
When I saw the price of the complete tensioner assembly that BMW wants you to purchase, I decided that I'd try and find the wheels themselves. That saved some significant money.

Thanks for the info,

Does the wheel come with the bearing as a sub-assembly that can be fitted to the original tensioner? Did the wheel have wear?

Hopefully I can get some more owner feedback before buying the bits and doing the work.

Yes, the new pulley wheels fit onto the original tensioners.
The replacement pulley wheels come with new bearings.
My pulley wheels showed some wear, but the problem was that the bearings were dry.

Here's a shopping list for all of the pulley wheels:

DIY: idler pulley replacement [#47]

Davisca455 wrote

Yes, the new pulley wheels fit onto the original tensioners.
The replacement pulley wheels come with new bearings.
My pulley wheels showed some wear, but the problem was that the bearings were dry.

Here's a shopping list for all of the pulley wheels:

DIY: idler pulley replacement [#47]

Thanks mate, bought all the parts except the water pump because the car hasn't done load of miles and they seems to be reliable for a lot of years.

including thermostat (plus o-rings), temp sensor, a new coolant reservoir cap and coolant the parts came to £850! That is from the Stealers mind you.

i also read that guys use cardboard to protect the radiator while you're fumbling around down there which seems a good plan

If I just need to replace the tensioner for the alternator belt, I understand I need to remove water pump pulley (can I reuse old pulley and does it come off without a puller?). The water pump pulley is blocked by maybe an idler pulley. Does that idler need to come all the way out or can I get it to the fan and have room to remove water pump pulley? Asking because I really don’t want to remove the fan again it was a PITA especially with supercharger.

Thanks!

IM Buddy8 wrote

If I just need to replace the tensioner for the alternator belt, I understand I need to remove water pump pulley (can I reuse old pulley and does it come off without a puller?). The water pump pulley is blocked by maybe an idler pulley. Does that idler need to come all the way out or can I get it to the fan and have room to remove water pump pulley? Asking because I really don’t want to remove the fan again it was a PITA especially with supercharger.

Thanks!

I replaced my alternator, belt, tensioner and tensioner pully last night.
Do you really need to remove the water pump pully if you're just replacing the tensioner? (EDIT: I see now...water pump pully blocks access to bolt holding tensioner). Getting the water pump pully back on was tough. It just has has 4 10mm bolts holding it on. No need for a puller but its a tight fit between that idler pully and the oil filter hard lines.
The idler thats blocking the water pump pully could be loosened but not removed because of the oil filter lines. I had to remove the other belt from that tensioner and play around with the water pump pully to find the perfect angle. Probably used a good bit of force as well.

Adding a little more detail here on torque specs. After looking around the forum for awhile I convinced myself that all the 8mm bolts that secure the tensioners are torqued to 40nm. The short ones accepted the setting while the longer one on the right side (alternator) came up to this setting more gradually.

I didn’t like how it felt, so I pulled everything out to make sure I didn’t strip the aluminum threads on the motor.

The pics tell all…40nm is way too much for the longer 8.8 grade bolt as it stretched it significantly.

The shorter bolts are higher grade and can tolerate that higher torque setting.

I haven’t found a clear torque setting for this bolt, but from this experience it should not go past 20nm.