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1M views 4K replies 593 participants last post by  ///Mark_D 
#1 ·
This post is for you if you just purchased your E46 and/or have more than 75,000 miles on your current cooling system. The E46 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 an E46 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 E46 cooling system. If your temperature gauge does go into the red zone, shut off the car immediately and have it towed.

How, why, and when do the failures typically occur? The number one cause of cooling failure for the E46 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.

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

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. 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.

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 and Clutch
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)

The Parts
OK, Mr. Mango, you have convinced me to replace the entire cooling system. Where do I get the parts? We have many great part sponsors to choose from here. Please visit the E46Fanatics Vendor section to see which vendors suit your needs best. The List of the parts that make up the E46 Cooling System which I recommend replacing.
  • Radiator
  • Expansion Tank
  • Expansion Tank Cap
  • Water Pump
  • Radiator Hose Lower
  • Radiator Hose Upper
  • Expansion Tank to Pipe Lower Hose (VERY important)
  • Thermostat
  • Radiator Fan Switch
  • Coolant Temerature Sensor
  • Water Pump Pulley
  • Coolant drain crush washer at engine-block
  • Water pump pulley bolts (reuse if careful)
  • Belt Tensioner Pulley (main pulley)
  • Alternator Deflector Pulley
  • Coolant
  • A/C Tensioner Pulley - Mechanical
  • A/C Tensioner Pulley - Hydraulic
  • Alternator/accessory belt (main large drive belt)
  • A/C belt (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)
  • Automatic Transmission Fan blade (recommended)
  • Automatic Transmission Fan Clutch (recommended)
  • Automatic Transmission Cooler O-Rings (two)
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.
Bleeding
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.
CAUTION: ONLY DO THIS WHEN CAR IS COOL AND ENGINE IS OFF. At no point should the engine be turned on.
ATTENTION: DO NOT EVER UNDER ANY CIRCUMSTANCE BLEED OR PERFORM WORK OR INSPECTION ON A HOT COOLING SYSTEM. IMMENSE BODILY HARM CAN RESULT

Here is a quick cheat sheet.
  1. Raise front of car on ramps (Not necessary, but recommended)
  2. Remove expansion tank cap and bleed screw and set aside
  3. Turn ignition to ON (dash lights on but do NOT start the car)
  4. Set heat to MAXIMUM (90) and fan speed to low (this opens heater valve)
  5. 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.
  6. 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.

FAQ
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, FCPEuro, or in some cases people like BMA out of Los Angeles. Up to you.

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!
 
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#1,255 ·
* E46 Cooling Guide (Information w/parts list/bleeding) *

Nice thread is nice.

1) has anyone found a replacement bolt that passes through the pulley for the A/C tensioner?
2) was there a consensus reached as to whether to swap the mechanical tensioner for the hydraulic type? I am thinking that so long as mechanical tensioners remain available, continue replacing with mechanical tensioners.


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#1,256 ·
Nice thread is nice.

1) has anyone found a replacement bolt that passes through the pulley for the A/C tensioner?
2) was there a consensus reached as to whether to swap the mechanical tensioner for the hydraulic type? I am thinking that so long as mechanical tensioners remain available, continue replacing with mechanical tensioners.


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Yep all my pulley bolts have been replaced on a PM basis. (so constant tweaking them doesn't round them out one day)

I'd leave the a/c one mechanical if it's mechanical. in fact i'd just keep whatever you have
 
#1,274 ·
* E46 Cooling Guide (Information w/parts list/bleeding) *

Quick question a while back my EXpack burst so I bought a new one a thermostat and belt so after that it was fixed no more over heating good to go ! So last night I was at a car meet knowing my electric fan was inop I spaced out and let my car Idling (talking to a cute 25i driver lol) all of a sudden my bleeder screw blew out and it was a disaster anyway I replace it today top it off with some 50/50 and no more over heating...the issue is my coolant tank light keeps coming on BUT I'm sure I put enough in could there possibly be a piece of bleeder screw in the tank blocking the sensor...maybe I don't know I'm going to try bleeding it again or something it just confuses me because it goes away and them pops back on


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#1,275 ·
Quick question a while back my EXpack burst so I bought a new one a thermostat and belt so after that it was fixed no more over heating good to go ! So last night I was at a car meet knowing my electric fan was inop I spaced out and let my car Idling (talking to a cute 25i driver lol) all of a sudden my bleeder screw blew out and it was a disaster anyway I replace it today top it off with some 50/50 and no more over heating...the issue is my coolant tank light keeps coming on BUT I'm sure I put enough in could there possibly be a piece of bleeder screw in the tank blocking the sensor...maybe I don't know I'm going to try bleeding it again or something it just confuses me because it goes away and them pops back on


Sent from BimmerApp mobile app
Positive your coolant level is correct? did you reuse your hoses when you replaced your expansion tank and thermostat? You should replace anything that hasn't been replaced. Weakest links will become weaker and just as this happened, you'll experience a:

-pop

-pop

-pop

They'll happen at different dates and will put you at high risk for permanent engine damage or dangerous situations while being stranded in a bad area at night.

Ensure your coolant level is fine when car is cold. If fine, then double check your sensor is plugged in. Pull it out and inspect - no coolant will leak out.
 
#1,276 ·
Bought this UV dye light kit for $15 for troubleshooting my friend's mysterious M3 coolant loss. Found the leak after one day of driving. Going to drive a few more days and recheck. Pic speaks for itself:

UV Light Dye Kit





Then I got curious and went on Amazon and found an even bigger LED UV flashlight :evil:

EVEN BIGGER UV 51-LED flashlight



Apparently it's OK to leave this stuff in the oil and coolant. I really don't want to put it in my coolant if I don't have to. Tomorrow I'll check if BMW coolant naturally glows or has some kind of dye in it?

I read some engine oils come with UV dye in it already. That's interesting. Never thought to try this stuff out. :thumbsup:
 
#1,277 ·
Bought this UV dye light kit for $15 for troubleshooting my friend's mysterious M3 coolant loss. Found the leak after one day of driving. Going to drive a few more days and recheck. Pic speaks for itself:

UV Light Dye Kit





Then I got curious and went on Amazon and found an even bigger LED UV flashlight :evil:

EVEN BIGGER UV 51-LED flashlight



Apparently it's OK to leave this stuff in the oil and coolant. I really don't want to put it in my coolant if I don't have to. Tomorrow I'll check if BMW coolant naturally glows or has some kind of dye in it?

I read some engine oils come with UV dye in it already. That's interesting. Never thought to try this stuff out. :thumbsup:
 
#1,279 ·
Makes things easier to spot. It'd be nice to just inspect the engine bay with a light to spot the tiniest of problems with a quick pass of a UV light. I guess that's why they make oil with uv dye in it already.

http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9042838&contentId=7076439





The formulation also contains a fluorescent color that becomes visible under UV light – this represents our signature of authenticity and quality, guaranteeing top performance.
 
#1,280 ·
I guess my point was you're going to detect oil in plenty of places where you'll do nothing about it. Oil gets everywhere on an engine.
And any meaningful leak where you'd want to replace the OFHG or VCG will be more than enough to not need UV.

But I do want one of those cool flashlights!
I've got a 100 LED light that looks the same, and got it for the same price, but it's visible spectrum.
 
#1,281 ·
Yeah my car is pretty dry so far knock on wood but really you shouldnt have any oil anywhere. But a lot of times oil leaks can be hard to pinpoint and UV dye would show where fresh leaks are. especially if you repaired/replaced one thing and you think you still might have leaks, this might help.

Yeah i ordered this flashlight. amazon is dangerous =/
 
#1,282 ·
Re: * E46 Cooling Guide (Information w/parts list/bleeding) *

Thanks to mango for his awesome detailed information. Helped me when I needed to replace the belts this week; replaced wp, thermostat and pulleys. Et is less than yr old so didn't replace it. PM is always key with any car. Better to be safe than sry IMO. Now I have to find some rubber for my 17s so I can give my bro in law his rims back lol

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#1,288 ·
That's it. Eeps! The lower left portion that the tensioner bolts into, broke off, it's still attached to the tensioner. That's the bad news. Good news is it failed in the driveway.
Gotta love this car, it always goes down at, or close to home.
 
#1,293 ·
Ok, thank you. I know you helped me in my thread about replacing my camshaft position sensor, do you think if I could do that, with the help of a good DIY I could do this cooling system overhaul in a couple of hours?

I know for the most part there isnt anything super hard about doing this, but just more of the dickin around to get stuff in place and properly. Im concerned about not being able to get the serpentine belt off and replace the water pump. It seems that it is just one screw on one of the pulleys that loosens it?
 
#1,294 ·
Where you are is needing to read and watch more DIY's for this. Few hours is ambitious for the first time for doing a cooling system. Watch youtube vids.
Fan on an auto car is more intimidating than the serpentine belt removal. That is easy.
Remove fan and then stick a torx or allen socket (I forget which) into the tensioner bolt and turn slowly CW until the tension is off and you can slide the belt sideways. Easy even the first time.
What all parts are you going to replace? Include Rad? ET? Thermostat for trans? WP? Thermostat? Give us your whole list.
 
#1,295 · (Edited)
Expansion tank
Water pump
Thermostat
Water pump pulley

Ive been looking over DIYs for this for a decent amount of time. Ive got a pretty good idea of what I need to be doing. Its just going to the be the actual removal of some of the parts. Like the expansion tank. Would it make it a lot easier to have the car raised up when doing this? I know you have to access the bottom of the ET to unclip it and what not. The water pump and thermostat seem pretty straight forward.

Going to definitely do this on a weekend to allow myself the most amount of time.
 
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