Monday, October 27, 2014

The Definitive Mango BMW E46 Cooling System Blog with Complete Parts list and tips!


This blog post is for you if you just purchased your E46 3-Series and/or have more than 75,000 miles on your current cooling system on your E46 3-Series BMW.

The BMW E46 3-Series is among certain BMW models that are known to to suffer from cooling-related failures, often times catastrophic due to warping the engine block.

The 6-cylinder in your E46 is a straight six design featuring an aluminum head and block.  This design has inherent benefits for which BMW engines are known for.  However this design also has inherent drawbacks.  When overheated even for seconds, the long aluminum head on a BMW straight six is particularly vulnerable to warping.  The fix is a risky and costly top end engine rebuild or a complete engine replacement.  The cost is $3,500 and up.

When a BMW  3-Series overheats, the result is usually a blown headgasket causing coolant consumption, coolant/oil mixing, or an overpressure situation in the cooling system.  Either way, the car will not run long during any of these three conditions.  This happens to so many people on a daily basis but can easily be prevented with $500-750 worth of parts every 75,000 miles.

As such, it is absolutely imperative that you maintain your BMW E36/E46 3-Series cooling system.

If your temperature gauge does go into the red zone, shut off the car immediately and have it towed.

BMW E46 Complete Cooling System List 9-26-16
Mangos Engine including Rebuilt Cooling System

Appreciate your support over the years and using my links--I earn a small amount when you use them and it doesn't affect you at all.  Much love! 

The List.  11-16-17

1) Radiator
(Manual transmission) link to buy
(Automatic transmission) link to buy

2) Expansion Tank

3) Expansion Tank Cap

4) Water Pump

5) Radiator Hose Lower

6) Radiator Hose Upper
link to buy

7) Expansion Tank to Pipe Lower Hose (VERY important)
link to buy

8) Thermostat

9) Radiator Fan Switch

10) Water Pump Pulley
URO Aluminum link to buy

11) Coolant drain crush washer at engine-block

12) Water pump pulley bolts (You can reuse these if you are careful)

13) Belt Tensioner Pulley (Main central pulley)

14) Alternator Deflector Pulley
link to buy

15) Coolant
link to buy

See this thread before ordering to make sure which A/C pulley you need. 

16) A/C Tensioner Pulley - Mechanical
Dayco 89133 link to buy

Alternative:**Thanks To Terra, you can also buy BMW X5 part for your hydraulic tensioner.  #11287549557  it comes with a backing plate you won't be using. Discard it. Just reuse your bolt**

16) A/C Tensioner Pulley - Hydraulic
link to buy

17) Alternator/accessory belt (Main large drive belt--The same across all model year cars)

18) A/C belt (Differs dependent on your build date--see below)
link to buy (5-rib production date up to 9/2002) 

link to buy (4-rib production date from 9/02)

Expansion Tank Mounting Plate Manual Transmission (Optional--You may reuse--For manuals only) link to buy

If your E46 has an automatic transmission, you'll need to add at least some of the following parts to the above list:

Automatic Transmission Expansion Tank Mounting Plate (Again, optional--you may reuse)
Genuine BMW link to buy

Automatic Transmission Thermostat (often crumbles apart upon removal of original--DO NOT GET CAUGHT WITH YOUR PANTS DOWN ON THIS--REQUIRED FOR AUTOMATICS)
Genuine BMW link to buy

Automatic Transmission Fan blade (Optional yet recommended)
Genuine BMW link to buy

Automatic Transmission Fan Clutch (Optional yet recommended)
HELLA link to buy

Automatic Transmission Cooler O-Rings. (Highly recommended as the old ones tend to not seal the same) Order two of these for the transmission cooler.
OEM link to buy

Prices, information, and brands/prices/links subject to change. These are current as of 9-25-16

The total cost for manual cars is around $500. For automatic cars, around $750 which includes the fan blade/clutch.

The failures:

How, why, and when do the failures typically occur?

Expansion Tank

The number one cause of cooling failure for the E46 3-Series is the expansion tank This tank has a 100% failure rate and fails on every single E46, usually around or before 90,000 miles.  This can be installed in your driveway in 45 minutes or less using simple hand tools.  If you can change a light bulb, you can change your expansion tank.

Some fail sooner than that while some last longer.  These tanks fail because of heat cycling of the plastic material they are made of.   Typically the failure will make itself known when you see a yellow low coolant light on your gauge cluster.  You will open the hood and the tank will look fine but what you don't see is the hairline crack that formed down the side of it, usually invisible to the naked eye.  This crack expands under pressure and water spews out either while driving or when the car is parked.  Come back to your E46 and there's a puddle under it? Yep that's your expansion take 9/10 times.   If the water/coolant level becomes low enough, there will not be enough coolant for the water pump to circulate.  No circulation means no flow through the engine/radiator. No flow through the radiator/engine means overheating and a $5,000 engine replacement and lost down time, towing fees, rental car fees, headaches, etc. Again, buy here.  DO NOT BUY THIS AFTERMARKET IF OU CAN AVOID IT.  GENUINE BMW ONLY.  Genuine BMW is maybe $20 more but it's worth it.  If you do not buy Genuine BMW, you may buy OEM which as of time of writing, is the brand CoolXpert.

If you just need the expansion tank cap, buy here. It's good to keep a spare cap or replace at 25,000 mile intervals because the seals on the cap are known to harden and lose their ability to seal, even between tank replacements.  They're around $12 -- good investment.

Pulleys and belt(s) systems 

Our M5X and S54 engines have three belt-driven tensioner pulleys. The role of the tensioner is either to provide belt-spacing/traction and to quell crankshaft vibrations due to irregular accelerations from the crankshaft. This is done to prolong the life of belt-driven accessories and likely to quiet engine operation.

When should you replace your pulleys?

If your pulleys are original: replace them.

If you don't know how old they are: replace them.

If they are noisy or have excess play: replace them.

If they have 60,000 or more miles: replace them.

This is a crude diagram of the front of an M5X engine: 

The main belt drives the water pump, alternator, and power steering pump.  This belt is guided by pulleys.  These pulleys contain ball bearings and grease.  After around 60k miles, this grease dries up and the pulleys are vulnerable to failure.  The belts are then thrown off once this pulley fails and you now have no cooling system, no power steering, and no charging system.Your dashboard will light up like a christmas tree and your temp needle will fly into the red zone.

Belts.  Obviously the belts themselves can fail causing an otherwise brand new cooling system to not operate. Replace every 35k miles. You can find it here.

This belt system is no joke.  E46s are prone to pulley failure.  I've seen it time and time again.  Is your E46 squealing and whistling?  Replace your pulleys. They're cheap and very easy to replace.

See my thread here for more info and discussion:

Water Pump

The water pump is another potential failure point but admittedly not as common.   It can fail in at least three ways. 1) The impellar itself will break and cannot continue to push water.  2) The seal may leak and, 3) The bearings will fail causing the shaft to wobble and break which will in turn throw the belts off effectively rendering your cooling system useless.

You might hear nightmares of water pumps with plastic impellars, but don't pay attention to this.  Replace your water pump due to age and/or mileage, not because what its made out of.  The latest BMW water pump design (at least 10-15 years old) features a plastic composite impellar.  BMW did once try metal impellars but quickly phased those out due to premature balancing and bearing failures.  Design is more important than physical materials.  Some people insist on installing the Stewart water pump.  Some recent reports suggest that these are low-volume production items and may fail prematurely. Others report success.  It's up to you.  If you insist on the Stewart water pump, it can be found here.

You'll need to remove the fan on your automatic E46 to access the water pump. I recommend this fan clutch tool here:


Generally fails in the open position leading to a "cold" temperature needle on your gauge not allowing the car to warm up, this item can leak as well or worse yet, fail closed or partially closed.  It's a good idea to replace it.  Thermostat can be found here.


The E46 radiator is typically robust, but the end tank seals are rubber and harden over time. You'll notice staining or slight weeping.  The radiator has thin passages which can become clogged with sediments as well and may cause water to flow slowly to where it needs to go. This may cause problems in traffic or while stopped.  The plastic end tanks may also fail but this isn't that common of a failure mode for this part.  They are cheap enough to replace anyway and is one of the most vital cooling parts--arguably the most important one.  Don't skimp on this.   Manual Trans unit here and Auto Trans unit here.

Fan blade and clutch
(for automatic transmission equipped vehicles).

Another failure point.  If the blade chips or deteriorates, there goes its balance and will explode in your engine bay.  There goes your belts, hoses, hood and whatever else it feels like taking out.  The fan clutch is typically robust, but is good practice to replace it anyway.  It controls the speed of the fan. You don't want it spinning too slowly or too quickly. A fan that cannot blow sufficient air over the radiator will fail to cool the water/coolant and thus the car will overheat. This typically happens when the car is stopped in traffic, say at a red light.


Written specifically by Mango

In order for your car to not overheat, these basic requirements have to be met:

1) Cooling system must be filled to capacity. That is to say the system must have no leaks and no air bubbles or pockets in it. Car must have correct amount of coolant/water.

2) Water must be able to be driven without any unnatural hindrance. That is to say the water pump must be able to push water throughout the system without added blockages or weakened drive force due to a damaged water pump or slipping/missing belt. The thermostat should also be opening and closing as designed.

3) Air must pass over the radiator in sufficient quantity at the correct moment. That is to say your mechanical and/or electrical-driven fans must be operating correctly when triggered by properly working sensors.

If your car is overheating, at least one of the above is not being met or you have bigger problems with the headgasket (unlikely if you've never overheated before)

If your car is overheating at idle (say in traffic) and you are sure that 1) you have adequate water in the system and 2) said water is air pocket/bubble free, then air is failing to blow over the radiator. You need to investigate why. Either the fan(s) aren't operating properly (not blowing air or enough air) or your fan switch isn't telling the fan to turn on. (or both) Or you have debris between your radiator and condenser. Time to break out the a toothbrush and garden hose.  Remember you must have proper coolant/water flow and proper air flow!! You need both.


Bleeding the system: (VERY IMPORTANT-DANGER DO NOT SKIP!!)

This step is extremely important. No amount of brand new cooling parts in the world will work if you do not bleed the system properly.  The point of bleeding is to remove air bubbles/pockets.  The cooling system is most efficient when it is circulating only fluid. Heat cannot radiate away from the surface of the radiator if there's air pockets.  You are essentially reducing the size of your radiator significantly if you have air pockets running through it.

Here is the official procedure per BMW TIS:

Here is a quick cheat sheet on how to bleed the BMW E46 Cooling System:

Raise front of car on ramps (Not necessary, but recommended)

CAUTION: ONLY DO THIS WHEN CAR IS COOL AND ENGINE IS OFF. At no point should the engine be turned on.

1) Remove expansion tank cap and bleed screw and set aside

2) Turn ignition to ON (dash lights on but do NOT start the car)

3) Set heat to MAXIMUM (90) and fan speed to low (this opens heater valve)

4) Begin to fill your expansion tank with ideally a 50/50 mix of Genuine BMW coolant and distilled water (do not use anything else--no reason to.  The proper stuff is cheap)  The system might take a while to swallow the water.  Massage the hoses if you think it will help.  Keep pouring.  Water will begin to pour out of the bleed screw hole with air bubbles.  The point is to keep filling and filling until the bubbles are gone.  This may take a while--be patient.

5) Once you are satisfied that a continual stream of bubble-free water is emerging from the bleed hole and that your cooling system is adequately filled, go ahead and replace the bleed screw (do not overtighten).  The expansion tank will be full to the top at this point so you'll need to siphon off any excess so that the appropriate tank level can be achieved.

Congratulations! Your E46 is now ready for another 75k miles of trouble-free driving.  Never will you have to worry about being stranded with your wife, girlfriend, pets or kids in the car.  Never will you have to worry about posting a thread asking why your car is overheating or why your engine is stained with coolant. Never again will you have to worry. (at least for another 75k miles) :thumbsup:  The mileage is just a guide. Your results may vary.

Happy motoring

Appreciate your support by using my links. I earn a small portion when you use them and it does not affect your price at all.

For inquiries:


  1. How difficult would you say it is to redo the entire cooling system?

  2. Not hard at all. Basic set of tools and about 5 hours if your first time. Carefully study everything and how it connects and you'll be good. Take pictures along the way. good luck!

  3. I would love to pay you in beer or Sake if you prefer for your time watching over me whIle I attempt this rehaul

  4. Replaced: Exp Tank/Cap/Therm, Waterpump, Thermostat, Up/Lo hoses, Heat Control Valve, Radiator drain plug, coolant sensor. My son overheated with cracked Exp Tank, after it cooled, I added prestone, but after replacing parts used BMW coolant on light flush (1.5gal refil)- (taking to BMW for full flush later). After all of this my Eng Temp Gauge runs at Noon (idle or 65MPH) - But I have no heat. Fans work up and down so control unit if fine. I believe I fully bleed the system on ramps. So any ideas (outside of heater core?) e.g. bad repl Therm or ATF Them, any other sensors? I know heat is all about circulation but I cannot find a diagram anywhere online for 01 325I Automatic Coolant Flow (e.g. Eng toValve, valve to Core, Core to Exp Tank). Any thoughts or guidance/links? BTW great write. BMW tho expensive, surprisingly ease to work on for the coolant system at least.

    1. Look at the heater control valve. It sits in under and behind the intake box.

    2. The heater control valve is normally open - allowing coolant through the heater core. When the heater control valve is engaged it blocks coolant flow to the heater, this happens when air conditioning is requested.

      If your symptom is lack of heat try disconnecting the heater control valve. If this produces heat your heater control unit (in dash) is probably keeping the heater control valve engaged all the time - this is a common failure mode for the heater control unit. You should also bleed your system again with the heater control valve disconnected to flush air out of the heater core.

      If your problem is lack of air conditioning you should suspect your heater control valve.

  5. How much coolant do I need for a 323i e45 m54.. also I drained the entire block and radaor... system is empty.

  6. BMW coolant not listed on list or total price. Obvious, but don't forget to buy some!

  7. I have a 02 325xi and replaced the aux (electric) fan. This fan still won't turn on at all. After checking all the fuses I still have no place to look to find out what part has failed. This is a sensor problem as far as I can tell, but where is the sensor, what is it called?

    1. Same issue. I've put a meter on the wiring to both the temperature sensor and the emission sensor. Wiring is not the issue. I hear the emission sensor will give you a warning in the dash.. the temperature sensor directly below the plug for the aux. Fan checked out and showed signs of clear resistance change from when the car was cold to hot. Not sure what to make of it..

    2. Same issue. I've put a meter on the wiring to both the temperature sensor and the emission sensor. Wiring is not the issue. I hear the emission sensor will give you a warning in the dash.. the temperature sensor directly below the plug for the aux. Fan checked out and showed signs of clear resistance change from when the car was cold to hot. Not sure what to make of it..

  8. Our pneumatic factory was founded in 2000,CHECK HERE. In decades of serving China pneumatic industry, we have built our reputation on product knowledge, world class suppliers, application support, and value add services. Our commitment to our employees, customers and vendors is the core of our business beliefs. In our factory, there are more than 80 front-line workers, 3000 squares working shop.Our main products are air Pneumatic Cylinder, solenoid valve and also a lot of pneumatic fittings like Air Gun.

  9. 2003 325i Just replaced expansion tank, thermostat, water pump, fan blade and shroud. Fan blew apart and luckily just took out shroud. Have a leak. Blew in expansion tank and water comes out at location just under front of intake where fitting comes out of engine hooked to what is hard plastic or metal tube going towards back of engine. I can see the fitting when looking straight down between VENOS oil port and front of intake. Can you tell me what the fitting is called? Thank you

  10. Thanks for your blog. It is a great source of information. I am a french people with a 1999 323i E46, 164k Miles (262mKm). The water pump and expansion tank was never changed ! The thermostat was changed in 2002, it was a BMW service operation.
    I made an Inspection II and I bleed the coolant system, threee month later the expansion tank has a leak. Fortunately I follow all your recomendations, I changed the expansion tank + cap, water pump, thermostat, tensioner pulleys and belts.
    The old water pump, tensioner puleys was nearly dead ...
    I am not a beginner in mechanics but I want to write about how to connect hoses, with the lock, you must heard a "click". You must do a correct bleeding of the coolant system, I find this short video very efficient and instructive ( )
    Thanks again Mango !

  11. Thanks for the blog - great info.

    Having recently gone through a catastrophic cooling system failure I'd like to add my 2 cents about some components that have not been mentioned.

    Temperature Gauge

    The temp gauge on an E46 is buffered and will show 'normal' (12 o'clock) from about 75-100C. It will give you very little warning of overheating or underheating problems, to see the actual coolant temperature in digital format on the dash use the onboard computer test menu #19 submenu #7.

    Electric Cooling Fan.

    Some E46 models have an electric fan, some have a mechanical fan, and some have both. On a model with a mechanical fan (clutch driven) the electric fan is supplemental; but on a model with no mechanical fan the electric fan is the only way to create airflow through the radiator when the vehicle is stopped. A failed electrical cooling fan is therefore a common cause of catastrophic failure at low speeds - in my case I was waiting to pickup my son on a hot day with the aircond on and boom the expansion tank exploded with no warning at all. The upshot is that if you have an electric fan you need to regularly test whether it's working or not, because the car will give you no indication that it has failed. They are a variable speed affair with three connections - power, ground and a pulse width modulated duty cycle - so they're not easy to test on the bench - but should come on briefly when you start the engine, should come on all the time when you have air conditioning on, should come on if you disconnect the coolant temp sensor at the lower radiator hose.

    Expansion Tank

    These are very sensitive to over-filling. If the float level indicator is pinned to the 'max' position then you have too much coolant in the system - keep the float level mid-way between the low and high positions.

    Heater Control Valve

    The heater control valve is an electro mechanical switch that controls coolant flow through the heater core. It is normally open, allowing coolant through the heater core, and is driven closed by the heater control unit when air conditioning is requested. These may fail electrically and be open all the time, or they may fail mechanically and stick open or closed. To diagnose a heater control valve while it is on the vehicle ask for heat, disconnect the valve electrically and check that both hoses become hot. If they do the valve is normally open as it should be. While still asking for heat reconnect the valve electrically and check that both hoses remain hot. If one of them becomes cool the heater control unit is incorrectly closing the valve when heat is requested. Next ask for air conditioning. This should close the valve and one of the hoses should become cool.

    Heater Control Unit

    These engage the heater control valve when air conditioning is requested, but they commonly fail in a way that engages the heater control valve all the time. The symptom of this problem is no cabin heat. See above for diagnosis, but to summarize if you have no cabin heat disconnect your heater control valve. If that produces heat your controller is faulty.

    Auxilliary Water Pump

    Some models have an auxilliary water pump under the heater control units. The purpose of this pump is to cycle coolant through the heater core after the engine is turned off, but they may also be used effectively to bleed the cooling system. You need to be aware of whether you have one of these or not.

  12. Some additional thoughts about bleeding the cooling system

    There are lots of instructions out there on how to do this, but in general the instructions presume that a) you have an auxilliary water pump, b) your heater control valve / heater are operating normally, and c) your thermostat is operating normally and opens electrically. You should understand what equipment you have when you are bleeding the system and you should keep your circumstances in mind - if you are trying to correct a problem it's possible that the problem itself is preventing you from bleeding your cooling system correctly.

    If you have an auxilliary water pump and everything is operating correctly you can effectively bleed your system without starting the vehicle. With the engine cold remove the radiator cap and bleed screw, turn the ignition to start, and set the heat and the fan to max. This opens the heater control valve so coolant flows through the heater core, engages the thermostat heater to open the thermostat, and engages the auxilliary water pump to circulate coolant. You should be able to hear the aux water pump operating and (if you have enough coolant) you should see in the expansion tank neck a needle of coolant flowing. Add coolant to the expansion tank until it starts running out of the bleed screw holes with no air present, and then close the bleed screw. Squeeze the RAD and heater hoses for awhile to help any trapped air escape. Slowly add coolant until the float gauge comes off bottom, and then turn the ignition OFF. Adjust the final expansion tank fill level with the engine off, and be careful to set the level between min and max. Don't overfill - use a hand pump to remove coolant if you need to. Do all this preferably with the front end of the vehicle on ramps to help air escape more easily.

    If you do NOT have an auxilliary water pump everything is basically the same, except that after closing the bleed screw you need to run the engine while you fill the expansion tank.

    Finally, if you have any doubts about the health of your heater control unit you should also disconnect the heater control valve to ensure that coolant circulates through the heater while bleeding.

  13. I am doing the 75,000 mile coolant maintenance. Water pump, fan blade, expansion tank have all been replaced. Problem the heater pipe is leaking where it comes out of the engine. I bought a new heater pipe and am having trouble replacing it. There is a support bracket under intake manifold that I can't get to without removing intake. 2003 BMW 325i shop manual has no info on replacing this pipe. Any helpful suggestions are appreciated. Thank you

  14. I've had issues along with some others using the gates hoses where the seals lose their seal and start to leak. I ended up buying the BMW part for 5x the price after dealing with the leak for a month.

  15. BMW coolant not listed on list or total price. Obvious, but don't forget to buy some!

  16. I've been getting an Auxiliary water pump error on my 2001 325i. There is no such thing but only the water valve which I replaced along with a new water pump, thermostat during a cooling system overhaul. Any idea what else it could be?

  17. Wonderful article, such a great information. I really appreciate your writing skills.
    Plumbing Pipe Fittings Composite Piping System

  18. Your blog is good and awesome. Help full for all. Corsnet is the leading manufacturer company for steel pipes. Visit:

  19. Your blog is good and awesome. Help full for all. Visit:

  20. Thanks for the info. Check out quality parts inspection system parts from

  21. November 27, 2015 at 5:49 am
    It has been my belief that great writing like this requires exploration and also talent. It’s very apparent you have done your homework. Incredibly good work!

  22. Thank you for your post. This is excellent information. It is amazing and wonderful to visit your site.
    transmission rebuilding tools

  23. Nice Website...
    Hey JOIN now and Increase Facebook Likes your profile and websites.
    Increase Facebook Likes and check your website worth worth my websites
    FB Likes and check your website worth Website Value Calculator
    Hot Wallpapers
    its may be very beneficial for you also really

  24. Your approach to this topic is unique and informative. I am writing an article for our school paper and this post has helped me. Thanks.

    Equinox Oxygen Concentrator

  25. Nice Website...
    Hey JOIN now and Increase Facebook Likes your profile and websites.
    Increase Facebook Likes and check your website worth worth my websites
    FB Likes and check your website worth Website Value Calculator
    Hot Wallpapers seo tools website
    its may be very beneficial for you also really

  26. Thank you for helping me to avoid E46 pitfalls.

  27. Thank you for helping me to avoid E46 pitfalls.

  28. Hello , can I use prestone 50/50 coolant from Walmart ? Why can't u use the concentrated full antifreeze ?

  29. A Hydraulic cylinder is also called a linear hydraulic motor, which is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. For more details and updates of hydraulic cylinders visit us at :

  30. Wonderful contribution to the state of our cars! Thank you, Mango! Call into my radio show today, May 3, at 1-2 p.m. EST and talk cars with me!

  31. Never open your radiator when the engine is hot. The pressure in the system can cause hot coolant to splash out and burn you.
    radiator coolant in Pakistan

  32. I hope you can help. I have a 2003 325ci and it has started to over heat. I have changed the water pump, thermostat, fan clutch, expansion tank and it still over heats. It does not have any of the signs of it being a blown head gasket so what else could it be.

    1. It can be anything you haven't changed yet. You need both water and air to flow in a sealed environment in order to stay within operating temperature. You have to find out where the chain is broken.


Let Mango know what you think!