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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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#762 ·
Mr Mango, I wish my son had read your post. He drove our 318i (2002 4 cyl auto) when the coolant lights came on and blew the engine at 94 000 k's. I replaced the motor and the gearbox at the same time, seeing that I had a 2003 30 000 k car scrapped as a result of collision damage as a donor. The young man has learnt his lesson, I think. He now travels with coolant - ready mixed - in the boot and will hopefully start reading the advice on this site. I find your and jfoj's advice invaluable. Keep up the good work in 2013.
 
#765 ·
CrazyOneToo. They were talking about Silicone dielectric grease, commonly referred to as "o" ring grease.



Mango: I'm about to do the cooling system overhaul, I replaced my thermostat 2 years ago exactly. It has roughly 25k miles on it, should I replace it as well or can it wait a couple more years to the next coolant change? BTW its a Wahler.
 
#769 ·
The $40 or so you'll save isn't worth the chance that a half-life'd thermostat won't fail requiring you to take apart the system again and go through the whole process. Also the less you remove the hoses the better--the seals weaken every time you play with the hoses. Better to do it once.

There's documented cases of brand new Behr AND Wahler thermostats failing after only one year.

I'm only recommending this because OP will be in there anywhere. My Wahler has 30k miles on it and so far so good. But if I was in the OP's position, I would definitely replace it.

Is $40 worth the peace of mind? your call
 
#771 ·
TIP: for people doing cooling system work, buy some O-ring lubricant, which is essentially just a silicone grease with minimal additives. It makes all the O-ring connections go on and come apart significantly easier. You'll happily spend the $12 for a large tube of it if you've ever dealt with a sticking connection. The O-ring safe grease is also good for preventing corrosion of metal parts like electrical terminals and waterproofing and lubricated sealed connections so it's a versatile product. I recently used this on a cooling system job last week and it was worth every penny.
 
#783 ·
Decided that because my upper and lower radiator hoses and expansion tank has not been changed for 60k miles to change it plus the thermostat.
Here is the problem......the lower radiator hose seems to be baked onto the radiator and will not come off when the spring clamp is released. Tried everything--but afraid that I will damage the radiator if I force it anymore.
Is this common---any suggestions, please........
 
#788 ·
Nope--did not come off in 5 minutes.. But the Lower Hose did come off in 1 hour (I exaggerate--about 20 minutes--even though it was 1 hour of aggravation )
Guys--thanks.........Now, new upper & lower hose, thermostat, expansion tank....that should hold me for another 60k. (I have a Steward water pump and decided not to change it until 150k--maybe)
 
#789 ·
Thank you for the good information here. I plan to do this my 325ci. I have a question regarding the temperature gauge and wondering if anyone can validate this. I was told by a knowledgeable BMW owner that the coolant temperature gauge is either not accurate or nonworking on all e46s? I have two E46s, the 02 325i (automatic) gauge responds quicker than my 04 325ci (5-speed). The 325i's heater warms really quick, the 325ci takes time and the needle is barely in the center. Any thoughts much appreciated.
 
#790 ·
Oh man o man did I fk it up today :tsk:

I over torqued a bolt putting on the thermostat. It's still somewhat tight but it's fkn stripped...

So the thermostat is held in with 4 bolts, 3 10mm's and a 13mm. The 10mm bolt underneath the 13mm bolt (one on the right) is stripped.


Has this happened to anyone?

Is it as easy as rethreading it to a different size? Luckily it was the bolt on the right, not the ones on the left that are directly holding the thermostat in place.


Any assistance and help would be great :thanks:
 
#794 ·
Also...for anyone questioning mango madness about replacing all the coolant hoses....check out the recommendation from Gates. Gates is one of the leading manufacturer of coolant hoses.

Epdm hoses are the latest in coolant hoses technology. BMW currebtly uses Epdm.
With the reduction in engine compartment size, coolant hoses are prone to failure due to the prevalence of factors such as heat, abrasion and oil. In addition, new conditions arise, such as electrochemicaldegradation.

Gates has determined that electrochemical degradation, or ECD, results when the hose, liquidcoolant (ethylene glycol antifreeze and water), and the engine/radiator fittings form a galvaniccell or "battery." This reaction causes microcracksin thehose tube allowing coolant to penetrateinto the reinforcement.

Accelerated by high-heatand flexing, thehosecan develop a pinholeleak or rupture under normal pressure. This possibility of hidden reinforcement failureisoneof the best reasons for replacing coolant hoses every two to four years.

To address the damage caused by ECD, Gates has developed an electrochemically-resistant ECR coolant hoseusing a special EPDM (ethylene propylene rubber) formulation.


sent from my HTC EVO+ using Bimmer App
 
#796 ·
Half reasonable question, but the answer has nothing to do with your trunk battery as the explanation has battery in quotes. This means they are not talking about your battery, but the "battery" that is created between different electrogalvanic materials.
However, you're in luck because our hoses do not connect to metal as we have plastic connectors on our radiators. So given plastic on the end of our hoses, and plastic on the rads, we do not have dissimilar materials mating to one another.
Bottom line: relax and cruise easy.
 
#797 ·



Cooling System Overhaul Advice Requested. (Mango, thanks very much for taking the time to provide the above parts list. I'm new to BMW's and this forum, though I have been studying both of them for 3 weeks. About 3 weeks ago, I purchased a 2002 325Ci, (JW52135) with 153K. The service records for the first 64k came from BMW since this was a Lease vehicle. The next owner had it for about 10K, then the guy I bought it from had owned it from 75k till I bought it from him. The guy I bought it from had it serviced by the same Indy BMW Garage, (with receipts) till I bought it. The car has been pretty well maintained with regular oil changes. The only issues are the typical BMW issues I've found on this forum and the car is in need of a Cooling System Overhaul to include a radiator, since there is a hairline crack around the neck. None of the receipts I have indicate the cooling system has ever being touched, except for 20k ago, the Indy BMW Garage replaced the Thermostat, a Radiator hose and the belts. I will be driving this car btw Tampa and Miami at least once a month. I want to minimize my chances of a breakdown, so I'm trying to look at what could possibly give me a problem. The one thing I have not seen addressed with regards to the cooling system are the Heater Hoses and Pipes, (RealOEM. com schematics) in the system. So my questions:
1. As you well know, there is a lot of plastic on these cars, so I have to believe these heater pipes are plastic as well and suffer from the same heat/pressure related failures as the rest of the system, or are they more robust? Every vehicle I've purchased in the past the first thing I do is flush the system and replace the cooling system hoses, to include the Heater Hoses etc. What would be your advice for this BMW?
2. And with regards to the above post about the Expansion Tank mounting plate, should that be a wait and see or should I just go ahead and replace it?
3. I have a Hydraulic Tensioner for the WP/ALT/PS. Should I replace the entire Tensioner assembly or would the Tensioner alone be enough? The A/C Tensioner is Mechanical and independent of the rest of the system and looks to be pretty accessable and functioning properly for the time being. I think I'll leave it alone for now unless you're of a different opinion.
4. Voltage Regulator. Someone posted, (might have been you) that while you're down in the bowls of the engine compartment you should go ahead and replace the VR since these cars are particularly voltage sensitive. Your opinion?
Thanks very much for taking the time to address my questions.
 
#798 · (Edited)
1. I have not seen anyone ever report leaking heater hoses. Mango has been here longer so he can speak more on this, but I don't believe they are a concern. I think they are also pretty inconvenient to access.

2. If you have a manual transmission I think you can ignore the ET mounting bracket (plate). The automatic cars use this plate as a junction for the transmission cooler. I have an auto and I will be replacing mine with the ET as it is leaking slowly.

3. The hydraulic tensioner is quite expensive. Rather than buying the whole unit, you may just want to see if you can convert to the mechanical. I don't know if this is possible. If not, then the critical components are the hydraulic arm and the pulley bearing. Those two things need to be replaced probably.

4. If you want to take care of it go ahead. You can at least check it's condition by removing it and inspecting the alternator's brushes. If they are getting small, just replace it. I don't know too much about VR failure though. Mango can tell you weather or not it shows symptoms before failure, or if it just dies out of the blue like the fuel pump.

Since you asked for Mango, he can verify what I am saying or correct anything I have gotten wrong, but I think I've pretty much got the gist here.
 
#802 ·
Thanks everyone for your input. I stopped by my local BMW dealer today to order a missing alternator duct and while there I asked about the water pipes. As luck would have it, they had one in stock that I was able to peruse. Pretty stout stuff. I'll inspect mine when I get stuck into this overhaul and if I see something wrong, I'll replace it, if not I won't. Also, if I run into any snafu's I'll let you know.
On another note, I've done some price shopping the last few days for the items I'll need for this overhaul. Though they don't have the best prices for everything, they do have the best price for many OEM items I was looking for, for this overhaul. And that would be BMWPartsSource.com an online source for Faulkner BMW in PA.
Thanks again everyone.
 
#804 ·
Hey all, longtime creeper. just made an account to post some questions. Really quick, working on a 2000 323i automatic transmission with about 90k miles. Previous owner never performed maintenance so i'm getting a crash course in it. Noticed a steady antifreeze drip coming from the expansion tank area under pressure so i started doing some snooping. Found this hose attached to the bottom of the expansion tank with a steady drip coming out of it.


Due to the location of the hose I had to remove the expansion tank to get in and pull it loose. Followed an excellent DIY found here supplemented with EdzGarage videos off youtube and eventually made it happen. The expansion tank was incredibly hard to remove, eventually pried it out by leveraging a screwdriver against the cap on top. It finally popped loose and this is where things get dicey. There is now an interesting rattle inside of my expansion tank, and I found pieces of the thermostat laying in my driveway (spring and copper colored metal piece). At this point I stood up and reached for my metaphorical emergency whistle while yelling "I need an adult!"

Is my sneaking suspicion correct that now I also need to purchase a new thermostat instead of just the leaking hose?

Any advice or insight is welcome, posted pictures of the pieces I removed.

 
#806 ·
Since your cooling system is falling apart, you should do the overhaul that Mango describes at the beginning of this thread.

For future reference, you can easily remove the expansion tank by using a long socket extension (10"). Put that up against the bottom of the ET and then put the other end on your jacks lifting pad. the jack will pop it right off.
 
#812 ·
Also in addition to what I said over PM, the effectiveness and pressure of the PSI setting you use to blow the water out will depend greatly on how many holes you've opened up in the cooling system. As I mentioned, just do enough to evacuate all the tap water. you don't want to blow anything. i used a reversed shop vac with 3 ports on the engine open and all went well

If it's any consolation, virtually everyone who takes off the ET breaks the auto trans thermostat. So they usually start the job with a new one on hand and just replace it.
Better yet, if you're working on part of your cooling system knowing that nothing has been done for so many miles, why not just replace it all to prevent the dribble of breakdowns spread out over the next couple years. This is what most of us here do.
Cooling system is the most vulnerable one and has the potential to wipe out the whole engine in a few minutes if you're not on alert for just a short while.
:thumbsup:
 
#811 · (Edited)
If it's any consolation, virtually everyone who takes off the ET breaks the auto trans thermostat. So they usually start the job with a new one on hand and just replace it.
Better yet, if you're working on part of your cooling system knowing that nothing has been done for so many miles, why not just replace it all to prevent the dribble of breakdowns spread out over the next couple years. This is what most of us here do.
Cooling system is the most vulnerable one and has the potential to wipe out the whole engine in a few minutes if you're not on alert for just a short while.
 
#814 ·
Luckily I only broke the thermostat (I assume its broken because I was picking pieces of it up off the sidewalk) instead of going for a home-run and breaking the sensor also. This forum has been a lifesaver for all the DIY information, I started out with 0 BMW mechanical knowledge and a grim determination to not pay close to $500 in labor. So far I can destroy at least 10 more parts at this rate and still come out ahead of going to my local mechanic.

Thanks to everyone who has taken the time to document their work!
 
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