Sunday, 12 October 2014

BMW E90 N46B20 Water Pump / Thermostat / Thermostat Housing

DIY Disclaimer: I hold no responsibility should anything goes wrong when you decided to follow my guide. It’s strictly meant as a reference for knowledge sharing purposes.

2007 BMW E90 N46B20

Mileage: 108k km

Been losing 500ml coolant weekly.

Photo taken from beneath the power steering pump.

2014-09-26 20.54.16 

I have no idea where the leak came from due to limited visual access but I can confirm it is from one of the water pump components. And losing fluid at 500ml a week, I can’t be keep topping up and dilute my coolant mix which is not healthy for the engine.

So I decided to take the plunge by buying all the components for that location (just in case), including one of the short hose.

Item 1: Water pump: 11 517 511 221

Item 2: Thermostat: 11 537 510 959

Item 4: Thermostat Housing: 11 517 572 859:

Item 7: Connector: 11 517 542 128


.. and Item 1: Water Hose: 11 537 572 159


2014-10-04 17.00.07

The spark plugs are for different project. Smile with tongue out

The rubber O-ring came with the water pump are not utilized because the rectangle one already available in the new thermostat housing while the round shape O-rings are for the old connector which was designed differently. New connector as you can see from the photo above at 4 o’clock location is entirely coated with rubber.

Workshop guide:



1. Our E90 N46B20 power steering pulley actually do not have the 3 holes to reach for the 2 water pump fastening bolts. Hence the only way is to remove the power steering pulley. Slacken the 3 x T40 bolts on the power steering pulley before remove the V-belt. The tension provided by the belt help securing the pulley from spinning freely. The pulley is very light and made of plastic material.

2. Use a size 16mm wrench to tension up the V-belt tensioner and release the V-belt.

3. Remove the power steering pulley.

4. Slacken the 2 x T40 bolts fastening the water pump to the power steering pump. These bolts are very tight. My Torx key set failed me because it bent when I apply force:


I had to order this:


5. Now the tricky part. The 4 x T45 bolts is hard to reach. Luckily they are not extremely tight compared to the above. The “L” shape Torx key excels. The T45 bits I bought is mostly hopeless here due to the narrow access.

Below is how I slacken (NOT RELEASE) the T45 bolts and if you are confident, you can release the water hose connections as it will give you a bit of extra room:


6. Water hose disconnection. Start from the top. Lift up the metal clip (refer bottom picture, from point A to point B) and wiggle your way out, 3 hoses connected to the thermostat.


7. Disconnect the thermostat wire located at the bottom of the thermostat.

Got the following from Pelicanparts. Similar connector. Just press the metal clip to the green arrow’s direction and pull the plug off.

pic10.jpg (1536×1047)

8. Now you can release the 4 x T45 bolts. The water pump connector may still be hanging to the engine and require some prying to get it out.


9. After both the power steering pump and water pump is out, then only I remove the 2 x T40 that fasten the power steering pump and water pump together. Water pump can then be taken out. Viola!


Removal took less than 45 minutes. Installation is not easy. Remember to fasten both power steering pump and water pump together before attempting the 4 x T45 power steering pump mount. Do not forget the connector at the water pump. Very tricky to put it back in because it keeps jumping out.

All in, I spent 4.5 hours to complete the job, inclusive of beer break in between.. Started 8:30pm, completes 1am.

More photos for references:

Power steering plastic pulley can be open using the T40 Torx key. Notice the V-belt still in place.

2014-10-06 07.23.01

After taken out the water pump:

2014-10-11 21.35.11

Check out the thermostat top water hose. Size 10mm bolt. Also you will notice the water pump connector below the exhaust manifold.. took me a while to get it out. Actually mustn’t apply force as it gets tighter. Just need to repeatedly tap it to get it out. Ya, I replace the connector too.

2014-10-11 21.36.01

The old water hose, lucky I replaced it. Ya, I applied gasket maker here too :

2014-10-12 01.22.14

Another view at the stubborn connector:

2014-10-11 21.36.32

Bottom view:

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Back view:

2014-10-11 21.39.58

Check out all the screws and bolts taken out. How do you like my metal screw pan? I believe we bought it from IKEA toy section when my children were young. It was on the way out to the donation bin when I rescued it and turn it into a screw pan by adding few magnets at the bottom. Viola! No more losing screws.. Smile with tongue out

2014-10-11 22.11.29

Old versus new. I apply gasket maker whenever possible. In fact, I’m suspecting my leaks are from these areas and not the water pump.

2014-10-11 22.17.25

This is how I open the thermostat, using a 1/4” bit. 7 of these screws. 3 to secure the thermostat to it upper housing and 4 to secure the water pump.

2014-10-11 22.30.15

2 bottles of 1.5L coolant with 6L of distill water. Still plenty left.

2014-10-12 01.21.04

That’s all for now! Thank you for reading and please provide feedback or query if any.. Winking smile


  1. This comment has been removed by a blog administrator.

  2. Thanks for the good diy article
    Really appreciate your effort to write it

  3. Thanks for the good diy article
    Really appreciate your effort to write it

  4. i am wondering e90 320i is using electronic water pump, is that possible to covert into mechanical pump?

    1. Maxim,

      It's not electric. Only the e90 325i uses electric water pump. We are using mechanical pump.

  5. really ? then we are lucky i think.
    i am newly bought a used 320i e90 2007.

    and i am quite worry about the electronic water pump. thanks for your info, i shall be feel better now. wahhaha

  6. How much did the components cost?


    1. Water pump: 11 517 511 221: $190
      Thermostat: 11 537 510 959: $140
      Thermostat Housing: 11 517 572 859: $65
      Water Hose: 11 537 572 159: $105
      Connector: 11 517 542 128: $50
      1.5L Coolant: 81 229 407 454: $23 x 2
      6L Spritzer Distill water
      Labor: 0 (DIY)
      Total: $596

    2. This comment has been removed by the author.

  7. Great Diy I just mine,on the weekend and looks good,but I have a rackling noise when I drive,any ideas

    1. Unless you didn't align the pump securely with the power steering pump.. but you can't fasten the bolt if that's the case.. try unstrap the fan belt and spin the power steering pulley by hand to detect the noise.

  8. Hi Chew, im getting electric coolant pump error code after having the high air temp symbol. I see you managed to change the pump yourself, did you bled the pump system after installing to ensure that there are no air pockets present? I read that it can be bled using GT1 soft?

    1. Unlike it's 6-cylinder siblings, the 4-cylinder e90 320i is not using electric water pump.

      It looks like your electric water pump is throwing out error code, you may need to replace your electric water pump.

      Bleeding the electric water pump cooling system is easy. No need GT1:

    2. Where did you get the distilled water? I asked my local hardware shop and they dont have it. Worst case, is it safe to use tap water instead?

    3. Bought it from a supermarket. Under the drinks/soda section.. look carefully, drinking water comes in different types:
      1. Mineral water
      2. R.O. (Reverse Osmosis)
      3. Distilled water

      99.9999% cars on the road uses tap water.. πŸ˜‚

    4. Managed to changed it last Saturday. Prying out the quick connector host is such a headache as there is not much room to have a good grip on the hoses. Anyways thanks for the tips and feedbacks!

    5. Haha.. it only need some side way knocking to slowly wiggle it out. It took me awhile too.. installing it also another headache..

  9. This comment has been removed by the author.

  10. Hi Astro

    hopefully you still check this blog, sweet article.

    Though what did you need to remove to get in here?
    So standard plastic air vent to access the engine, did you do any of the work below the car or just from above?

    I notice you say to only loosen the water hose connector, but then you seem to have pulled if off later on?

    1. Hi Matthew,

      The car wasn't jacked up, so ya, nothing from beneath. All works done by accessing from the above.

      The water hose, loosen the clip to detach. So ya, only pull off the end connected to the thermostat housing. The end connected to the radiator remain connected.


    2. Hi Astro. Going to do this today. How much coolant do I put in? I can't seem to find the info any where online

    3. It's about 6 to 7L.. but then again, it is not possible to drain 100%, so I assume around 6L. I will put 2 bottles of 1.5L coolant, and top up with distill water.

  11. Hi Astro
    Managed to find it in the end, 7.5 liters. But I lost a bit during the bleeding process, so close enough.
    Thank you man you've been so much help on this job!
    Only thing I can't figure out, is the coolant temperature, mine is reaching 105 degrees c. but I can't find much info on these 320i n46 engines.

    1. 105°c to 108°c operating coolant temperature is very healthy.. our thermostat remain shut at temperature below that..

  12. Thank you! Was thinking i'd have to take her to the mechanic in the morning to get her checked

  13. Hi Astro,
    Is it possible to remove the pump without removing the pump?
    I am about to do mine tomorrow, will there be enough space?

    1. Sorry, just saw your message.. not possible to get to the water pump without taking out the power steering pump.