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Old 04-06-2012, 11:14 AM   #1
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Join Date: Mar 2006
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Exclamation E46 COOLING SYSTEM GUIDE - overheating/coolant/etc

This 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.

I also have a blog post dedicated to the cooling system of the BMW E46 which can be found here with the most recent updates, price lists, etc: Mango's Cooling System Blog.

Also if you just got your E46 and want to ensure top notch reliability, see the Top 10 Parts that will fail on your E46. These are all cheap to replace! the Top 10 E46 Failures -- Aka "The Mango Starter Pack" which ironically, does not include a starter.

The failures:

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

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. 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. 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.

Other common failures are the pulleys and belt systems. 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 redzone. See my pulley thread here: Mango's definitive pulley thread

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

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.

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:

Thermostat. 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.

Radiator. 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.

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.


In order for your car to run at an optimal temperature and NOT overheat, these requirements MUST be met:

1) Cooling system must be filled to capacity. That is to say the system must have no leaks and no air 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 blockages. 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 working sensors.

If your car is overheating, at least one of the above is not being met. 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/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)


OK, Mr. Mango, you have convinced me to replace the entire cooling system. Where do I get the parts? (Shortcut, list of recommended brands here.)

We have many great part sponsors to choose from here as well. Please visit the E46Fanatics Vendor sections to see which vendors suit your needs best. You can also go on my website e46mango.com for great sources.

The List of the parts that make up the E46 Cooling System which I recommend replacing. 9-26-16

Expansion Tank
Expansion Tank Cap
Water Pump
Radiator Hose Lower
Radiator Hose Upper
Expansion Tank to Pipe Lower Hose (VERY important)
Radiator Fan Switch
BMW Coolant Temp Sensor
Water Pump Pulley
URO Aluminum
Coolant drain crush washer at engine-block
Water pump pulley bolts (You can reuse these if you are careful)
Belt Tensioner Pulley (Main central pulley)
Alternator Deflector Pulley

*See Pulley Guide HERE*

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

A/C Tensioner Pulley - Mechanical

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**
X5 A/C Hydraulic Tensioner Pulley

A/C Tensioner Pulley - Hydraulic
Alternator/accessory belt (Main large drive belt)

A/C belt
(Note: 9/02 and pre 9/02 models have different belts--check your model first!)

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

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)
Automatic Transmission Thermostat (often crumbles apart upon removal of original--DO NOT GET CAUGHT WITH YOUR PANTS DOWN ON THIS--REQUIRED FOR AUTOMATICS)
Automatic Transmission Fan blade (Optional yet recommended)
Automatic Transmission Fan Clutch (Optional yet recommended)
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.

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.

For more info on the complete list of parts you'll need, see my cooling post blog. (9/22) updates in the works.

**Additional hoses for additional security! (Less likely to fail but if you want to be thorough, some fanatics have replaced the 4 additional hoses:**
RETURN HOSE - Runs from the coolant connection fitting (automatic) / radiator mounting plate (manual) below the expansion tank to the front hard composite pipe near the throttle body.
INLET HOSE - Runs from the rear hard composite pipe beneath the intake manifold inlet runner number six to the heater valve inlet.
SHORT HOSE - Runs from the heater valve outlet to the heater core inlet.
LONG HOSE - Runs from the heater core outlet to the connector on the rear of the expansion tank, about halfway up. This hose runs on the chassis rail, higher up than the return hose.
**Thanks Clabcon for the added 4 parts.**

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 point of bleeding is to remove air bubbles. The cooling system is most efficient when it is circulating pure fluid.

Here is a quick cheat sheet:

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) The mileage is just a guide. Your results may vary.


Q) But Mango, isn't full cooling system replacement a waste of money?! Can I wait for the parts to fail and replace one at a time?
A) Preventative maintenance is a risk assessment. It boils down to your acceptable level of risk. For me, on critical parts, that's 0 or near 0. As the cooling system is the one aspect of the car that can bring your engine down with it requiring a full engine rebuild or replacement, that's one system you don't want to mess with.

I understand some people that argue this can't afford to maintain their cars or may be on very strict budgets so this issue is personal for them and they get angry and lash out but really we should all try to help eachother try and maintain our cars and especially not give newbies a false sense of security. I've given advice on partial cooling replacements as well.

If you're an adult, have a decent job, and need to get to work every day. Full cooling maintenance should be a priority if you own an E46. It's your way of life. It's how you put food on the table for you and your family.

But MANGO?! You mean to tell me $500 is all I need in the context of adult car ownership is all I need to spend protect my engine from total destruction? Deal of the century. Sign me up!

You are all driving once-$40,000 German luxury cars for $5,000. And you're going to complain if that car now costs $5,500 and is more reliable, to boot? What planet are we on?

$500 over 5 years is $100 a year. Or $8 a month. Is that too big of a pill to swallow?

Q) Mango, what brands do you recommend?
A) I recommend OE (Genuine BMW), OEM (parts like Behr, INA, Wahler, Rein, CRP, CoolXpert, Saleri, Contitech, etc.), or OEM or equivalent/higher such as Meyle HD pulleys, Graf, and in some cases Gates.

Q) Mango, where do I get the parts?
A) Plenty of E46Fanatics sponsors such as ECSTuning, FCP, or in some cases people like BMA out of Los Angeles. Up to you. I also have a full parts list and recommended brands here.

Q) My car has 50,000 miles, do I still need to replace xx part?
A) Rubber and plastics deteriorate with time. You'll probably be better off than a person with 90,000 miles but nobody can predict the future. If you want to be safe, I recommend full replacement. These cars are 12-14+ years old.

Happy motoring,
-Mangohttp://www.e46mango.com/2017/11/mangos-e46-bmw-cooling-system-e-store.html"]E46 Cooling Blog[/URL] for updates and cool postings and latest parts info.

Happy motoring,

Last edited by Mango; 12-20-2017 at 12:50 PM.
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