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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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#3 ·
Glad to help. There's also other misc. hard pipes and even one soft hose which connects to back of expansion tank and goes to the hard cooling pipe towards the firewall. But nobody replaces that but maybe I should add that too. I totally forgot about it when I did my cooling update. But, FWIW, I don't think I've ever heard of a hose failure on these cars.
 
#314 · (Edited)
I don't know if I have mentioned this before but I am replacing the return hose with the Samco silicone replacement. It's number 5 here:

http://realoem.com/bmw/showparts.do?model=BD52&mospid=47620&btnr=17_0215&hg=17&fg=05

The part number for this one is TB3966. It only costs £25 plus shipping so it's a bargain.

Much like the radiator hoses you reuse the OE hose ends with some hose clamps. I am going to buy new upper and lower radiator hoses and a return hose from the dealer to get hold of new o-rings, this is so I can measure them properly and source some better alternatives as well as have some 'in stock'. I will post the measurements in this thread:

http://forum.e46fanatics.com/showthread.php?t=906997

I already have the Stett Performance upper and lower radiator hoses. Samco do make the upper and lower radiator hoses but it's quite a new kit (TCS529C) so I had to buy the Stett hoses at the time (best I could find for non-M). This cost me about £200 all in whereas the whole Samco kit is only £85 :facepalm:

I am using the silicone replacements as I had the upper rad hose burst and leave me stranded, I thought it was worth it to get some stronger and longer lasting items :thumbup:
 
#7 ·
Bookmarked :thumbsup:

I bought a kit for my 330ci from Mike at the thebmwpartsstore.com. Really nice guy. You included some extra parts that I'll keep in mind. I just bought a 323ci and sell the 330ci so I'll keep my parts for the 323ci.
 
#10 ·
My car's PO purchased the car at ~100k miles and drove it from Florida back to MO. Somewhere along the way the coolant tank had cracked and leaked out all the coolant and it overheated. The PO turned the car off as soon as he saw the temp spike but by that time, it was too late and it lost the head gasket and warped the head.

He replaced the entire cooling system and had to deck the head and rebuild it. There's unfortunately nothing he could have done to prevent this as it happened on his way home after buying it. He was left with a 2k plus bill even after having super cheap BMW club people helping with the rebuild. It ruined his experience with the car which is why I have it now.

Plastics deteriorate with age just as it does mileage so even if you haven't put on 75k miles, if your car is ~10 years old, consider Mango's advice...change it out...
 
#11 ·
+1

Great story. How many miles on the rebuilt head? Glad to see its doing well to this day. And yes, age will also kill plastics. A lot of people come on here saying their E46 has 50k miles and thus needs no cooling maintenance. Nothing could be further from the truth.
 
#19 ·
What about the mounting plate that goes between the radiator and the expansion tank? When I was doing my refresh, the nipple that plugged into the radiator broke off when I removed it. Seems like this should be part of the refresh, especially since the o-ring that is on it seems to be non-serviceable. There is a difference between the manual and automatic mounting plates, so that has to be kept in mind. Nice thread. There is plenty of useful info in here. I just hope that I won't need it for quite awhile! :eek:
 
#20 · (Edited)
Sure, I can add the mounting plate. In my experience, it's a robust part and is essentially just a plastic frame. should be fine if you're careful. I'll add it!

Since this part isn't a typical failure item, I didn't include it in the grand totals. It's $54 and somewhat substantially drives up the cost of the rebuild.
 
#1,528 ·
Expansion Tank Mounting Question



New to forums. Have read a lot about coolant leaks and expansion tank. Had a slow leak at the temperature sensor. It finally got big enough that I had to attend to it. There was indication of leakage at the top of the expansion tank and I fought my way through removing it. When I looked from the bottom after removing it, I saw that the mounting plate seems to be loose from the radiator, but not sure how it is supposed to look. Any thoughts on the questions on the photo would be appreciated.

 
#23 · (Edited)
Great write up:thumbsup:

A bit jealous of those US prices, if I had those prices here I could afford the overhaul every 30k miles :rofl:

I had to do the cooling overhaul on every BMW I've owned, never replaced the radiator thou as I dont think it poses a danger at the mileage I had my cars with.
I havent heard of a rad failure before 100k miles so I personally dont recommend replacing it any time sooner then that. I was never for preventative maintenance and I still am against it. To me its just money wasted because I know exactly how long the parts can last before replacement. For example , early the water pump failures are usually on prefacelift automatic cars and are due to the fan clutch thats gets the water pump unbalanced. When I bought my current car at 96k miles , I took the water pump out and it slid as ROCK, no side to side play in the bearing whatsoever(pump was stamped '03). I still replaced it with a Stewart EMP because I was planning that anyway regardless of the condition of the old one, but it was quite interesting to see that OE one held so good. On the other side, I had an E39 530i before and only at 65k miles that I bought it with the waterpump was complete TOAST (way too much side to side movement). All E39s have a clutch fan (regardless auto or manual) so I can bet my money that it was the cause.

My current E46 is coming up for a rad replacement this summer, I purposely didnt replace the rad when I did everything else to see how long it would last, but now I think its time , dont feel like waiting anymore.

Another thing I'd like to add, I didnt see it mentioned or simply missed it.

The ET cap on our cars is the very big thing and gets overlooked WAY to many times. ET cap is a pressure valve in our cars, our cooling system is pressurized and runs at 2bar/29psi(on the bottom of the cap it says 200 kpa). Whenever the pressure gets higher the cap releases it (this is why you may see dried up stains of coolant on your ET eventhou its new and NOT leaking). Everyone knows that PRESSURE is the biggest problem , as its what gets our ET to crack. So, the less pressure you have in your cooling system the less chances you have of a failure.

E30s have a 1.4 bar/20psi ET cap (on the bottom it says 140kpa) which when installed on E46 will maintain a lower pressure in your system, thus having less chances of failure. Its a cheap and effective way to be protected.

'91 325i ET cap part # 17111742232

Another way to reduce pressure is to install a high volume water pump. We know that more water flow means less pressure .EMP Stewart is able to pump 20% more water thus reducing the pressure inside the system. How much less pressure??? I dont know, but even if it lowers by 3-5psi its worth it. They offer stainless steel High Flow water pumps that are also lifetime warrantied. This is the reason why I installed one in my car. Its not as cheap as the cap, this one will set you back $170 but in my opinion is well worth the investment
 
#25 · (Edited by Moderator)
Great write up:thumbsup:

A bit jealous of those US prices, if I had those prices here I could afford the overhaul every 30k miles :rofl:

I had to do the cooling overhaul on every BMW I've owned, never replaced the radiator thou as I dont think it poses a danger at the mileage I had my cars with.
I havent heard of a rad failure before 100k miles so I personally dont recommend replacing it any time sooner then that. I was never for preventative maintenance and I still am against it. To me its just money wasted because I know exactly how long the parts can last before replacement. For example , early the water pump failures are usually on prefacelift automatic cars and are due to the fan clutch thats gets the water pump unbalanced. When I bought my current car at 96k miles , I took the water pump out and it slid as ROCK, no side to side play in the bearing whatsoever(pump was stamped '03). I still replaced it with a Stewart EMP because I was planning that anyway regardless of the condition of the old one, but it was quite interesting to see that OE one held so good. On the other side, I had an E39 530i before and only at 65k miles that I bought it with the waterpump was complete TOAST (way too much side to side movement). All E39s have a clutch fan (regardless auto or manual) so I can bet my money that it was the cause.

My current E46 is coming up for a rad replacement this summer, I purposely didnt replace the rad when I did everything else to see how long it would last, but now I think its time , dont feel like waiting anymore.

Another thing I'd like to add, I didnt see it mentioned or simply missed it.

The ET cap on our cars is the very big thing and gets overlooked WAY to many times. ET cap is a pressure valve in our cars, our cooling system is pressurized and runs at 2bar/29psi(on the bottom of the cap it says 200 kpa). Whenever the pressure gets higher the cap releases it (this is why you may see dried up stains of coolant on your ET eventhou its new and NOT leaking). Everyone knows that PRESSURE is the biggest problem , as its what gets our ET to crack. So, the less pressure you have in your cooling system the less chances you have of a failure.

E30s have a 1.4 bar/20psi ET cap (on the bottom it says 140kpa) which when installed on E46 will maintain a lower pressure in your system, thus having less chances of failure. Its a cheap and effective way to be protected.

'91 325i ET cap part # 17111742232

Another way to reduce pressure is to install a high volume water pump. We know that more water flow means less pressure .EMP Stewart is able to pump 20% more water thus reducing the pressure inside the system. They offer stainless steel High Flow water pumps that are also lifetime warrantied. This is the reason why I installed one in my car. Its not as cheap as the cap, this one will set you back $170 but in my opinion is well worth the investment
Nice. I thought you were in the US? Your plate looks American-ish. Anyway good info and I agree the radiator usually lasts longer than 100k. But I mentioned that this is just a guide and your mileage may vary.

And the expansion tank cap is listed in the parts list. DODO HEAD! :banghead:

Please show us your radiator when its out so we have some documentation on E46 radiator failure. I want to know where/how specifically these radiators fail. I know the E36 radiators fail at the neck where the upper hose attaches.

Amazing write up :bow:

I myself will be doing my first real mechanical work in the following monthes.

Cooling system being number one, soon followed by ofhg, vcg, vanos seals.

Thank god for these forums, I will save a ton of money on labor!

Thanks again mango!
No problem, FenderGuy05!
 
#31 ·
I have it for about 20k miles.
Great write up Mango! Should definitely be stickied. :thumbup:

Btw there's a reason the cap is set for 200 kpa. Water under pressure will have a higher boiling point than water at normal atmospheric pressure. If you switch to a 140 kpa cap then you are lowering the efficiency of your cooling system.
True but the change isnt drastic to significantly reduce the efficiency but is big enough to reduce the pressure to prolong the life of ET.

Reason why I personally think E30s used a 1.4 bar cap is because back when E30s were made BMW didnt have the technology to make plastics (Expansion tank for the biggest part) withstand the pressure of a modern E46 cooling system which is 2.0 bar. E30s cooling systems are plenty efficient. E46s have a 2.0 bar system due to the fact that technology enables BMW to make ET with the plastic that can withstand the pressure, but as we clearly know E46s ET are cracking open all the time , its THE weakest point in the whole cooling system .

You do lower the boiling point of your cooling system but its still plenty enough to keep the car cool. The change isnt that significant to get scared off.

Its the same when using 50/50 mix of coolant. Its to raise the boiling point and, well mostly to prevent from freezing, but if your country never sees temp below freezing(and also not as hot as texas) you can drive on water only, sure the boiling point will be low but it'll never be significant enough.
 
#28 ·
Great write up Mango! Should definitely be stickied. :thumbup:

Btw there's a reason the cap is set for 200 kpa. Water under pressure will have a higher boiling point than water at normal atmospheric pressure. If you switch to a 140 kpa cap then you are lowering the efficiency of your cooling system.
 
#33 ·
Great thread! I agree with the Sticky idea... It will be easier to refer the inevitable cooling system questions here.

Another part I'd consider adding is the fan switch (13621433077, $20.97) and fan switch o-ring (13621743299, $1.32). These mount in the lower radiator hose and are a good idea to replace when replacing the hose as the old o-ring may not fit correctly in the new rad hose.
 
#35 ·
Thank you for taking the time to thoroughly put this together (parts, prices, places to buy)!! AMAZING.
 
#38 ·
I have a question with regard to omissions in the coolant carrying hoses. The two main radiator hoses are always mentioned to replace, but the heater core hoses and hose #5 in the diagram are never included. Come to think about it, I've never seen a mention on more than one e46 board of anyone ever having one of these hoses fail? Anyone?
And if I wanted to prophylactically replace the heater core hoses, are they not connected in impossible to reach locations?
I know the large hoses are under more stress, and smaller hoses can stand up to higher pressures more easily, but eventually all rubber will wear out. I'd like to hear from anyone who has already replaced these as preventative maintenance.
(or otherwise for that matter?)
 

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#39 · (Edited)
Stinger, I changed both hoses off of the expansion tank with my coolant refresh, 4 and 5, the other hoses from the heat control valve to heater core looked like they had been changed recently, I saw some rust stains underneath the car so it confirmed a leak there at one time in the past, nothing particularly tricky, the heater core connection was easy to get to when I was doing CCV so I already had the air filter tray removed, the connection under the intake was on there pretty tight but loosened up ok once I got a hold of it. My hoses were pretty spongy and were definitely ready to be changed but I did notice most DIYs don't mention these. I chalked it up to having high mileage.
 
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