E46 COOLING SYSTEM GUIDE - overheating/coolant/etc
This thread is for you if you just purchased your (99-06) BMW E46 3-Series 323i 328i 325i or 330i and/or have more than 75,000 miles on your current cooling system on your 1999-2006 BMW 3-Series (E46) or your cooling system has failed or overheated. This includes your belts, water pump, expansion tank, radiator, coolant leaks, etc. Warning--even a brief heating episode will destroy your engine in seconds. Don't get caught with your pants down. VERY common to overheat on BMW E36 and E46 3-Series cars.
For the most UP TO DATE and complete parts list, pricing, and other information, see the updated version of this cooling blog here for additional tips and tricks, reviews, etc here: Mango's Cooling System Blog. Also don't forget to check out the Top 10 E46 Failures -- Aka "The Mango Starter Pack" which ironically, does not include a starter.
The E46 3-Series is among certain BMW models that are known to to suffer from cooling-related failures, often times catastrophic.
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, a long piece of aluminum such as a BMW 6-cylinder head has a tendency to warp from heat really quickly ultimately destroying the headgasket and/or seal between the head and block.
Following an overheat, this damage doesn't take long to occur--anywhere from seconds to minute(s) depending on conditions. The result is usually a blown headgasket causing coolant burning, 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 or so.
As such, it is absolutely imperative that you maintain your BMW E36/E46 3-Series 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 3-Series 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.
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. 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
Belts. Obviously the belts themselves can fail causing an otherwise brand new cooling system to not operate. Replace every 35k miles.[
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. If you insist on the Stewart water pump, it can be found here:
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 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 not overheat, these basic requirements have to 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)
OK, Mr. Mango, you have convinced me to replace the entire cooling system. Where do I get the parts?
Cooling System List
Behr (Manual transmission)
Behr (Automatic transmission)
Expansion Tank Cap
Graf Water Pump
Radiator Hose Lower
Genuine BMW Radiator Hose Upper
Radiator Fan Switch
URO Aluminum Water Pump Pulley
Coolant drain crush washer at engine-block
Water pump pulley bolts x4 $0.25 ea.
MEYLE Belt Tensioner Pulley [/B]
MEYLE Alternator Deflector Pulley
A/C Tensioner Pulley
SEE THREAD (YOU WILL NOT FIND THIS AT THE DEALER OR ANY ONLINE BMW VENDOR! In a pinch you may find at Autozone but it wont show up in their computers. You have to ask for ac tensioner pulley. Ask them for all BMW pulleys for your model and look at them in person!
(mechanical, Dayco 89133 $21.94)
OEM Continental Alternator/accessory belt
A/C belt (5-rib up to 9/2002) $8.72
(4-rib from 9/02) $7.91
Genuine BMW Expansion Tank Mounting Plate--MANUAL TRANSMISSION--DO NOT BUY IF YOU HAVE AN AUTO TRANSMISSION. Link to automatic version below!
If your E46 has an automatic transmission, you'll need to add the following parts to the above list:
Genuine BMW Expansion tank mounting plate
Genuine BMW Automatic Transmission Thermostat (often breaks upon removal of original)
Genuine BMW Fan blade
CoolExpert Fan Clutch
Prices subject to change.
Grand total manual transmission cars: $500.23
Grand total automatic transmission cars: $738.20
For more info on the complete list of parts you'll need, see my cooling post blog. (9/22) updates in the works.
**Additional hoses for additional security!
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.
**Thanks Clabcon for the added 4 parts. GO UK!**
Bleeding the system: (VERY IMPORTANT-DANGER-DO NOT SKIP!!)
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.
Here is the official procedure per BMW TIS: http://tis.spaghetticoder.org/s/view.pl?1/06/06/86
Here is a quick cheat sheet:
Raise front of car on ramps (Not necessary, but recommended)
CAUTION: ONLY DO THIS WHEN CAR IS COOL AND ENGINE IS OFF. At no point should the engine be turned on.
1) Remove expansion tank cap and bleed screw and set aside
2) Turn ignition to ON (dash lights on but do NOT start the car)
3) Set heat to MAXIMUM (90) and fan speed to low (this opens heater valve)
4) 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.
5) 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) :thumbsup: The mileage is just a guide. Your results may vary.
Again check out my E46 Cooling Blog for updates and cool postings and latest parts info.
Great resource! I'll be sure to reference this when tackling my upcoming cooling system replacement.
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.
Couldn't hurt to include it anyway.
Excellent write-up, as always, and perfect timing. I will be doing the complete refresh this summer.
Sounds good! Thanks!
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.
I wonder if the mods would think its a good idea to sticky this since the cooling thing is asked about by newbies on almost a daily basis.
Should be stickied since everyone suffers from the cooling system issues at least one time in their ownership of a e46
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...
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.
This needs a sticky.
Request sent to SolidMod. Haha. Not to be off topic, but I noticed you have an M5, Halo. (Gorgeous car, btw. it looks perfect how it is in your pic) you mentioned you have other cars. Whats the other car? E46??
Thanks for this, I always see you going on and on about the cooling system and now there is one place to find all the information we need!
I was really paranoid so I had a compression and leakdown test and compression was solid across the board around 180-190 cold and leakdown zero on all cylinders except two that were at 1%. Solid as a rock now. The PO is an enthusiast and he had BMW certified techs doing the repair, so it was done right thankfully. They even went so far as to time-sert the block in case the aluminum threads had weakened from the heat and addressed vanos as well while in there.
Cooling system also looks to have been done right. I was given the order sheet from Pelican with every part replaced and it seems to be doing its job well.
It's not a death sentence, but it's definitely an expensive repair. I just went through and looked at his cooling system overhaul parts bill and it was 900, so you've clearly put together a very cost effective means of addressing it. :thumbsup:
Awesome. Yeah I don't even want to know what the dealer price would be for all these parts and labor. I'm guessing way north of $2,000
This was the labor bill for the head rebuild:
Valve job BMW: 192
Pressure Test: 60
Needless to say, he got a good price on all that. Dealership labor would be....significantly higher.
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:
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.
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