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Pelican Technical Article:

BMW Water Pump and Thermostat Replacement

Difficulty Level: 4
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

  This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series.  The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
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[click to enlarge]

     BMW cooling systems are known for being troublesome. The thermostat and water pump are two of the principle areas of failure. Some of the old-style water pumps have a plastic impeller that becomes brittle and breaks off after many years of service. BMW has replaced the plastic impeller in recent years with a metal one. If you know you have a plastic impeller in your car, replace it as soon as possible. Overheating problems are common on these cars, and if your engine overheats, you may find yourself replacing the head gasket, which is not cheap (see our head gasket replacement article).

     Begin by gaining access to the water pump. Remove the fan and belts (Projects 5 and 34), and remove all coolant from the system (Project 33).

     With your equipment removed, the front part of the engine should be very accessible. Remove the fan pulley from the water pump; it is held on with four small nuts (see Project 34). Loosen the four nuts that hold the water pump to the engine block. Then, using a rubber mallet, softly tap the side of the water pump. It should separate from the block after a few taps. Once the water pump is loose, pull it out of the engine block.

     With the pump removed, check the inside bore (where the water pump fits) for debris or corrosion. Use a wire brush to remove any corrosion or debris that may have built up there. Install the new water pump using a new O-ring. Place a bit of white lithium grease around the O-ring to ensure a good seal and to ease installation of the pump into the engine block. Insert the new pump, and tighten the four bolts that attach it to the block. Torque them to 11 N-m (8 ft-lbs) but no tighter.

     At this time, I recommend that you remove the thermostat housing (located above the water pump) and replace the thermostat as well. The thermostat is a relatively cheap part that fails easily and can cause your engine to overheat.

     This project details water pump and thermostat replacement on E36 engines. For information on E30 water pump replacement, please see the website.

     If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs.  If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one.  Your continued support directly affects the expansion and existence of this site and technical articles like this one.  As always, if you have any questions or comments about this helpful article, please drop us a line.

Figure 1
Shown here is the front of an E36 six-cylinder engine with the fan removed. The fan pulley is held on with four small bolts. When you remove the pulley, you will expose the water pump and its shaft (inset). The thermostat housing (yellow arrows) is made of black plastic and covers the thermostat assembly.
Figure 2
Tap on the water pump with a rubber mallet to free it from the engine block. The pump should pull off of the block after the seal is broken.
Figure 3
The old-style pump (right) has a plastic impeller and the new water pump (left) has an upgraded metal impeller. Although the plastic impeller does not have any broken pieces, the plastic has become very brittle and likely to break in the near future. There is no functional difference between these two—they will both pump the same amount of coolant through the system.
Figure 4
The interior of the water pump housing will most likely be coated with dirt and debris. Clean the inside bore of the water pump housing with a wire brush attachment and a hand drill prior to installing the new pump.
Figure 5
The new thermostat has been installed. Be sure to use a new O-ring to seal the thermostat to the cylinder head. Electrolysis caused by dirty coolant (see our article on Cooling System Flushing) has done some damage to this head. As a result, I applied a liberal coat of black silicone to the orange O-ring that is embedded in the thermostat housing (O-ring without silicone is shown in the inset photo). The silicone will help to seal the areas that have become somewhat porous on the cylinder head (green arrow).
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Comments and Suggestions:
Poti Comments: You guys have been really helpful just by reading the comments and stories. I have a 2003 530i with 117k miles. i just changed the intake and exhaust camshaft sensors and now the car has to be jumped to start. It ran well for one day with no codes but now the P0365 shows up again. it has a brand new battery! any thoughts?
January 4, 2015
  Followup from the Pelican Staff: Could be a bad connection or defective sensor. I believe that code would be for the exhaust sensor. Check the signal when the problem is present, should be a 5 volt square wave. - Nick at Pelican Parts  
aussie36 Comments: Hi.. first post and it's a happy one.. I recently purchased my first bimmer e36 and quickly discovered temperamental overheating issues.. after discovering pelican parts and doing my research I decided to replace thermostat, water pump precautionary and clutch fan car stayed reasonably cool with air con fan running.. I also found the radiator slightly blocked & gave it a good flush.. I'm pleased to say that today she's a very happy Beemer!! Thanks for great info.. helped ne a lot.. -tho coming from previous 4age 16v & 20v powered corolla's, the learning curve for BMW home mechanics was somewhat steep by comparison.. again, thanks for the very informative articles... Looking forward now to finding more power and getting the car on a better stance..
March 12, 2013
  Followup from the Pelican Staff: Glad we could help! - Nick at Pelican Parts  
Loveperlicanparts Comments: will these instructions work for a 2001 BMW X5, V6???
August 22, 2011
  Followup from the Pelican Staff: Your vehicle doesn't have a V6, if it is a 6-cylinder, it is an inline 6. This tech article is from a similar engine: /BMW/techarticles/BMW-3-Series-E46/28-WATER-Water_Pump_Replacement/28-WATER-Water_Pump_Replacement.htm - Nick at Pelican Parts  
shomo Comments: Does this work for a 98 m3??
June 11, 2009
  Followup from the Pelican Staff: Sure does! - Wayne at Pelican Parts  

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