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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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#1,629 · (Edited)
Hey Mango, I know you have "100% success rate" with the Behr radiators. Any of those were installed on an automatic without fitment issues?

Many people are reporting the same problem, including myself, so I'm sure it's not a user installation error. From my readings, I believed the fitment problem is only on automatics. I know OE radiators are slightly different between manual and automatic. Im just guessing here, maybe the mounting holes are slightly different, not just the drain plugs. But I read somewhere that Behr radiators for the manual and a/t are both the same design/mold. They just supply different a drain plug for each. I think that is where the problem lies.
 
#1,638 ·
Interesting. How is your expansion tank damaged, and how do you propose to repair it?
 
#1,647 ·
So have a question with the auxiliary fan.
I bought a 2000 328i manual a while back from a used car dealer, when the ignition is on the fan runs. I asked them what was up with it they said it was wired to run at all times because the old owner lived in Arizona and they didn't want it to over heat. I thought okay fine and use it as a bargaining tool. Well what I think what happened is the fan never shut off which seems like a common problem with that fan and they just Jimmie rigged it to bypass the relay and turn on and off with the ignition! Now here is my question is this a thing people are doing? I plan on getting a new fan and taking out the wiring they put in. Is this a possible? I just wanted some input before I start taking **** apart and spending money
 
#1,648 ·
So have a question with the auxiliary fan.
I just wanted some input before I start taking **** apart and spending money
It's not normal and it's not necessary. Sounds like dealer BS.
I spend time in Phoenix in 115 degree weather and the car runs just fine in traffic.

If you know what you're doing it would be best to find the part that prevents the fan from cycling and replace it while restoring the wiring to factory spec.
I'd suspect the relay failed and check that out first. If that's the case, best to not have fan current running thru the ignition switch.
Let us know how you make out.
 
#1,653 ·
Driving home from work last Friday...

Battery light comes on as I feel a little "burp" in the engine. Thought, "huh, there's NO WAY that new battery is bad already"...started to ignore the light for a second or two when I then noticed the RED engine temp light at the end of the needle's path light up brightly..."oh, sh!t"...pulled over immediately into a parking lot (as I saw steam exiting the hood and my power steering quit assisting) and shut it off. Shut down, I checked the bay: main belt shredded, a/c belt thrown off, alternator pulley "missing in action", disintegrated.

Now, I don't know what caused the whole thing but I ordered all new parts to do a complete (minus the radiator) cooling job. I unfortunately didn't come to the forum first, but I think I probably ordered a comprehensive amount of parts...$700 including an oil change, so about $640'ish I guess. [Note: I did opt for the EMP/Stewart hi-po water pump for $168, and I'm very impressed with the heft and build quality of the stainless-steel impeller setup]

Worried a little about head damage, but I have faith that BMW's are tough enough to handle a broken belt. If they turn out not to be, I may reconsider that M5 in my future! ;)
 
#1,654 ·
Hope you caught it in time! I think the odds are on your side.
Have you checked the coolant and the oil for cross contamination yet?

You could have saved yourself $100 with an oem metal impeller pump. But I have the Stewart myself too.
You are doing new pulley's (3) I expect? Either one of them seized or your belt wore out. The former is more likely I suppose.

Please come back and tell us how you make out.
 
#1,656 ·
Thanks.
I think it was the pully on the alternator that went, threw the belt into lots of moving parts, etc. the belt was only 15k old, and a Gator belt (good quality). I heard that pully squeal about a month ago, but it was intermittent, then stopped. Not being the smartest guy, I localized the sound to the alternator, and assumed I'd need a new one of those (and would wait for it to quit before doing so). Oops. ;)

Got about half my parts in. The ones i ordered from Oembimmerparts.com were shipped OVERNIGHT MAIL! Impressive! Got here Monday afternoon.
The ones from ECS will be here tomorrow.
Saturday project, I guess. Hopefully no rain!
 
#1,655 ·
Re: * E46 Cooling Guide (Information w/parts list/bleeding) *

If u caught it righ away youll be fine. My car overheated a week ago and it was fine. Stopped it as soon as i saw it. No problems at all.

BimmerApp on Samsung Galaxy S4
 
#1,657 ·
If u caught it righ away youll be fine. My car overheated a week ago and it was fine. Stopped it as soon as i saw it. No problems at all.

BimmerApp on Samsung Galaxy S4
Thanks...eases my mind a bit! :)
 
#1,658 ·
im having another issue with my 2001 330ci overheating
it just started random and led to replacing expansion tank and trans thermostat cause it was leaking and broke I also added a new temp gage sensor new cap and new top hose cause other one looked lil worn
so I begin to refill fluid and water keeps getting hot after few mins to the point of bubbling out if I let it but I shut it down figured just air pocket but no air is coming out so now I am turning to u guys I know ur all going to say head gasket but its been replaced last year thermostat was upgraded as well to better one not the old plastic one water pump has been replaced last year as well to my first question is prob dumb but is the push fan supposed to come on win hot or just when ac is on and 2 question is could it still be air lock and maybe I am just being to cautious please help I have no idea and tired of replacing **** and not having prob resolved
 
#1,659 ·
* E46 Cooling Guide (Information w/parts list/bleeding) *

While waiting for my parts, I did some YouTube searching. Found this 2-part series to be pretty informative.

You might want to check it out:
http://youtu.be/Mco77TK94GU


Sent from BimmerApp mobile app
 
#1,664 ·
Thanks guys. Since I'm most likely going with the Stewart pump (why not right? - just wish it was a bit cheaper!), might as well get the aluminum pulley also.

Once I got the fan out of the way I was surprised at how easy it is to work on the cooling system. I do enjoy working on my car but it seems to give me issues and make me spend money at the most inopportune times. lol
 
#1,666 ·
I don't know that you will be better off with the Stewart. As long as you replace the pump at 75k miles, I don't see much chance of catastrophic failure. AT&T he cost of the Stewart, it would have to last 250k to be worthwhile.

The aluminum pulley is only a dollar or two more from ECS.

I suggest you read some of Mango's posts on the Stewart and other metal impeller pumps.
 
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