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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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#167 ·
It's no SO important. It's a long shot that a very small number of fibre pulleys develop cracks which eventually lead to the pulley breaking and then shredding the drive belt. This then takes out a few cooling system parts and endangers the engine.
Al pulleys guard against this. How bulletproof do you want to spend money against insuring your engine?
 
#169 · (Edited)
Mango - I'm replacing everything today (inc. radiator). I need to transfer my expansion tank mounting bracket. I've got a manual transmission car, so there's no worry of a thermostat breaking. But: how do I wiggle off the expansion tank without breaking the bracket? Is that a common thing to happen?

Edit: nvm, since I need to transfer the bracket to the new radiator, I'll just try this idea:

http://forums.bimmerforums.com/forum/showthread.php?t=1756608
 
#171 · (Edited)
Results:

The Behr radiator is aptly named: it's a bear.

The expansion tank mounting plate screw holes didn't line up at all, and the screw hole for the radiator did not line up. I was very surprised by this. It took a few hours for us to figure out both problems. Other than the radiator, all OEM parts fit perfectly. I hope I did not damage my radiator during the install, but then again it could be defective since nothing lined up properly...never heard of this happening. Had to do a bit of drilling to get the mounting plate to work, and a lot of fenangling to get the radiator to seat right. I undid a large bolt sitting on the front of the car, no idea which bolt it was, but it held whatever the thing is that holds the radiator screw. I could move it around more easily by undoing this bolt, and was able to fit it in. Was not fun at all.

I learned the hard way that a torque wrench only works within its specified range and not below: I sheered a bolt off the water pump pulley. Lesson learned. I was able to get it out just fine, threads are not damaged, but all 4 of my bolts are stretched and should not be used at all.

I need to go to the dealer to get the 4 bolts for that, as well as a clip for the heater hose I somehow managed to lose.

Gonna bleed tomorrow morning and check for leaks, I hope I did everything okay. I followed the DIYs to the T.

Definitely don't wanna do that again, especially the engine block drain bolt. That sucker is hard to deal with without a big extension and a wobble attachment! Couldn't get a torque wrench in there, but tightened it til it was good and tight. Couldn't move it any more at all, so I should be good.
 
#172 · (Edited)
Update: Total success!

No leaks, no squeals from my belts, temperature is dead-center 12:00. Bleeding is interesting: Keep filling the system, even if you think it isn't full. It's about 3 gallons, so you'll use approximately 1 gallon of mixed coolant in a distilled water thing, and half a bottle of mixed coolant in a BMW coolant bottle. Check occasionally for leaks, just to be safe.

You'll hear the air start to escape from the bleed screw as the system fills up with coolant. When it finally tops off, coolant and bubbles will come out. You'll almost overflow your expansion tank, but it's okay. Keep watching the coolant level and wait for it to settle. You will see bubbles coming out of the bleed screw. When those stop, you're good to fire it up and test it. If you're successful, your car won't overheat (duh), and your heater will work full-blast.

Let your car cool down and check it hours later (or after work, in my case). Fill it with coolant as necessary, and you're done :)
 
#174 · (Edited)
Definitely not removing my aux fan just for all that ;) But if I were to re-do this whole thing again, I would get a Genuine BMW radiator and not a Behr. It seems that the fitment of the expansion tank bracket is iffy on these after doing some research. You can make it work, but be prepared for a lot of frustration and a little bit of drilling if you're unlucky and have a poor fitting one. Holes just don't line up well when putting it in the car, too.
 
#180 ·
I might've tossed those, but the order online says:

17-11-9-071-518-M6
Radiator, For Manual Transmissions, E46 323i/Ci, 325i/Ci/Xi (through 4/05), 328i (from 10/98), 328Ci, 330i/Ci (through 4/05), 330Xi (through 4/05)

Brand: Behr
What is the difference between the auto and manual transmission radiators? Would I have an extra coolant line? I didn't see any extra lines coming from the radiator when I was mounting it.

The only problem I had was getting the plastic screw hole to line up on the car itself, and on the expansion tank mounting bracket. Other than that, it fit in like a glove.
 
#179 ·
I just did the same thing with a Zionsville Autosport all-aluminum radiator. Had to file the fan shroud a bit to get it on, and the radiator either is a bit thicker or it won't seat quite so close to the AC condenser - the fan was impossible to get in there without removing an electrical connector on the exhaust side of the VANOS. Anyway, it's in there now, and I don't have to worry about plastic radiator ends.

They make just one design for both auto and manual (mine is manual). They provide a plug for the hole where the auto heat exchanger connects into the radiator, for those with a manual. My only misgiving is about the way that plug is held in - it has an aluminum bracket welded to it, which is held in place just on one side by the screw that attaches the ET mounting plate. So internal pressure will tend to force it off coaxial with its socket. Maybe just an old engineer getting too picky.
 
#182 ·
Zell, I think you must have the right version of the radiator. If I understand correctly, on the auto version, that hole in the radiator at the bottom end of the ET bracket is in communication with the rest of the radiator. If you had the auto version and didn't put anything in the hole, all your new coolant would just pour out. On the manual version, it's sealed off internally, and just used as a locating hole for that cylindrical protrusion on the ET bracket - which I had to cut off to mount the Zionsville radiator, because the hole is sealed off by an external plug for use on a manual.
 
#187 ·
Not sure what he did. Hard to tell since his engine bay and all parts are dirty. Which ones old and which is new?? Either case, either pump is fine. The idea is replacing a used quality part with a new quality part. Doesn't matter what the materials are.
 
#188 ·
Is there anyway to check if your cooling system might need to be replaced soon? I just got my car a few months ago, and it had 169k miles.

I got the car from an auction so I have absolutely no records of its past. However, the car is in great condition and was really well maintained, as since I've had the car the only thing I needed to fix was a vacuum leak. But anyways, since I have no idea when the last time the cooling system was redone, I wanted to know if I could be able to check.
 
#189 ·
If you have to ask, it has to be done. Otherwise you're just gambling, really. You might be able to see a date stamp on the side of the expansion tank or top of the radiator. That might be of some help. But really, it doesn't speak for the rest of the components. At 169k, there's bound to be a weakspot in your cooling system, if not the whole thing. Where in 818 are you?
 
#192 ·
Mango, thanks for this guide, I just recently bought a 03 330CI with 80k miles so I definitely want to do this but i have a couple dilemmas, one being I just moved here to Houston so I living an apartment complex and doesn't have garage. I don't have the tools and most importantly, outside of simple jobs I've never touched under the hood besides changing oil filter and wiper fluids and batteries. So is my best bet to buy the parts and take it to the dealer to have them install it or are there other alternatives you'd recommend? Thanks
 
#195 · (Edited)
If manual, just a ratchet, 13mm driver, 10mm driver, screw drivers, Torx bit (T25 i think?) or just buy a set. If auto, add a 32mm wrench for the fan nut (which is reverse threaded). When you remove the 32mm fan nut, you'll have to use a screw driver to prevent the water pump pulley from spinning. It's easy. just take it slow and pay close attention to how you position the screwdriver. everything can be done gently.

so to summarize:

remove air intake scoop
remove fan (mechanical if auto trans., electrical if manual) the elec. fan is just one torx bolt and one nut. unplug electrical connectors and pull straight up.
loosen tensioners using allen key or torx bit. Push down on your ratchet/allen key towards the drivers side to loosen tensioner so you can slip belt off. do this for both tensioners/belts.
then use same ratchet/allen key and turn same bolts to the left this time to remove the tensioners. remove the alternator pulley as well at the top using a 16mm (i think) socket. toss in trash.
remove engine hook at top (13mm bolts)
remove water pump pulley bolts (four 10mm)
remove water pump (four 10mm i think)
remove thermostat
drain radiator
remove hoses by undoing clips with a screwdriver
remove hose at expansion tank
pull expansion tank plastic handle clip to undo it
pull up on expansion tank (hard) pull and wiggle
remove radiator
reinstall is reverse
bleed properly using my instructions on the first page
do burnouts after

i may have forgotten a couple steps or maybe even got a step wrong but generally thats how you do it. its been a while since i did this
 
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