Cooling System Problems/Other possible problems with BMW E46 Engine??? Need someone who knows about this stuff!


Asked by Nov 14, 2012 at 03:17 AM about the 2002 BMW 3 Series 325xi Wagon

Question type: Maintenance & Repair

Have to put a new engine in 2002 BMW 325xi (E46). I have heard that the cooling system in this model needs some additional options or add-ons to stop the overheating problem that killed my first engine. Can anyone tell me more about this issue and how it can be fixed? Also, as I am putting in a used engine, any other suggestions on what I might need to do to ensure the engine will last a long time and not die again?? Yes, the engine has a warranty.

15 Answers


The cooling system on these cars only holds a small amount of coolant, so if there is any issues with the system, you can overheat fast. Rule of thumb is to replace the coolant parts every 60K so as not to have any issues. They sell a complete kit to take care of this problem.

16 out of 16 people think this is helpful.

the common routine, is the reservoir bottle (cheap plastic) cracks and needs to be replaced..not that bad of a job. easy with a lift. But people don't realize that. there is a sensor in the bottle, that should indicate when it is approaching unsafe temps!!!!! in the very bottom., if you disregard that/ it not show up, i have found more than not, the head gasket usually goes first, (right side). how did it "Kill" the engine? why was it not repairable? AND ALWAYS ALWAYS ALWAYS USE THE BMW COOLANT!!!!!!!!!!!!! it has additives the regular stuff does not.....might as well to a thermostat since you are in there. If you have to use water, use DISTILLED, the engines are so sensitive the minerals in tap water also break it the cooling fan working? let me know if i can help more

13 out of 13 people think this is helpful.

Thanks so much both of you! That's helpful. Okay, here's what happened: I bought the car in July, everything seemed fine. I took it on a road trip 8.5 hours in one day. On the way there (the first 8.5 hours) it did fine. Then, on the way back two days later I was about 3hrs from home and had been checking the temp gauge regularly, nothing seemed amiss. I stopped at a store and noticed there was a small amount of steam or smoke... but I checked the gauges and everything was fine, there were no indicators that anything was wrong and I didn't get any unusual smells so I continued on, keeping a close eye on all gauges. 1.5 hrs later there was smoke pouring out of the engine and no gauges were indicating any overheating issue. So I pulled over, turned off the engine. I waited about 30 minutes but nothing seemed to be cooling. My boyfriend opened the hood and tried to add some water to the coolant reservoir but he said he could see some coolant still in there, low but not empty. I turned the key to the "on" position to see if the gauges were indicating anything and boom, the temp gauge was all the way up and the check engine light was on. Then, after a long time of waiting and no improvement I tried to start the car and it wouldn't start. I had it towed 2 hours to a BMW dealer. A day later the mechanic calls me and tells me it overheated so badly it completely warped the aluminum head and caused irreparable damage to the engine. Now here I am. No warranty. The dealer I bought the car from, not a BMW dealer, has offered to put an engine in for free if I buy an engine. He says he found a used engine with like 88K for $3400, which sounds insanely expensive for how many miles are on it. The good thing is there is a warranty of 1yr/12Kmi. The reason I asked about the cooling system is I had heard that there may be additional fans or things to improve it to try to prevent this from happening again. Because this is a used engine I want to see if he will throw in a new cooling system or additional fan while he's in there, and maybe check the temp gauge (seems to be working now apparently) or get an additional thermometer that shows the exact temp at all times. Does any of this sound like a good idea? I have been offered by a BMW mechanic to sell the car, but I have a loan on the car, so I'd have to pay off the loan first. The dealer I bought the car from also offered me $1500 for the car as a trade which is WAY too low even without the engine, especially since I would still have to pay the loan (which would be added to a new car that I get). Any suggestions? I'm starting to think that paying off the loan and selling it would be a good idea, then trying to use that money to get into a new loan on another car.... what a bummer. Thanks, any suggestions are sooo helpful! I'm really at a loss here and the car has just been sitting at the BMW dealer lot for over a month now...

7 out of 7 people think this is helpful.

yes,i remember the original post, i think i commented on that one as well...did you order the engine or still looking? and additional fans I been on BMW's for 5 or so years now, never had an additional fan, nor room under the hood, nor heard of one. you can hard wire the fan to come on with the ignition and off when the key is off, that I have done upon request...the trick to BMW is use BMW components, coolant, and requirements, it isn't a Toyota or Honda, there's no universal crap, it is a corporation that invested over a million dollars to create the best "ding" tone for the "door ajar" reminder on the 5 series, so I assure you as far as engine cooling, do what they say, lol

4 out of 4 people think this is helpful.

Yes BMW engines don't like to be overheated at all. BMW has such tight tolerances with the cylinder head that you really dont have much clearance to plain the deck. As john had mentioned above the main problem is the plastic expansion tank cracking open and leaking. Also there is a lower coolant hose that has a temperature sensor in it for radiator outlet temperature. If the coolant temperature gets to hot it will kick on the aux fan (this is if you have an automatic transmission, you have a mechnical fan and an electric one ). If you have a manual your car uses and electric fan only for cooling. If you wanna help the cooling system after replacing it with all OEM parts and coolant add some Red line water wetter it helps cooling system effectiveness. Also replace the coolant temp sensor located on the cylinder head under the intake manifold. Hope this helps

6 out of 6 people think this is helpful.

John, No. I haven't ordered and engine yet. I have been looking online and it appears I could probably find one cheaper than that. I think the dealer is quite the scam artist. I'm not really sure at this point what to do. Probably I will put another engine in it but I'm not sure I want to take the engine the dealer is offering. Thanks both of you for your answers. It does help. So basically I should replace the entire cooling system every 60K? Or just the coolant reservoir? And where do I even buy BMW coolant? Lol. Didn't know they made such a thing. Well it sounds like there is a lot I can do... but it will cost me. Just like the car already has. Guess that's what I get for buying such a sensitive, high maintenance car. Does anyone know where I might find a good engine? Is it a good idea to take it to the BMW mechanic after the engine is installed to have them check everything out? I'm thinking so, even though I already owe them $ for diagnostic but I don't feel bad paying them at all they have been so helpful and patient, letting me leave it on their lot for over a month! Thanks for all the tips. Is there a way to check the sensor to make sure it is working properly? Or should I just replace it? I am assuming, hoping, that with the engine I put in it everything will work okay and it's under warranty. Also, one more question, My dad was saying something about a rebuilt engine... is that better than buying a used engine? I guess the BMW mechanic quoted one for him at a bit more than the used engine, but he thinks it might be worth it... Idk. Any ideas? Thanks!!! I'll let you all know if I think of anything else.

1 out of 1 people think this is helpful.

I have another question: my BMW is a 2002... but does that mean I have to buy a 2002 engine? Or is there a specific range of years for the 325xi engine that will work? This probably sounds pretty stupid. Sorry. Thanks!


no stupid q: BMW and Mercedes name their cars as the following: the first number/letter in the name indicates size chassis 3 : series bmw, (smaller frame), the following represent the engine 25, 2.5 liter...x is all wheel drive, and i, at 5 a.m. i forgot the i, will get back to you on that. But to answer it does not specifically have to be that year, the design change is every 5 years, but annually the companies tweak as much power out as they could. So ideally any 2.5 engine will fit in and work, if yours is not a 2.5, it may be smaller, 2.3 so before buying an engine just match the engine code 8th letter of the vin is the code for your engine, and make sure they match, try to get it close to the year as style changes can mean mounting differently. but that is a big difference in design.....

1 out of 1 people think this is helpful.

You wont have to replace the entire cooling system just the bottle (reservoir). Yes BMW makes specific equipment for their machines. German mechanics actually wear white lab coats and believe in rebuilding/repairing every detail there is so much pride, it is hard to get a car "totaled out" isnt as high maintenance as long as you do things correctly, and use proper parts, please for the sake of the car buy it, and throw average walmart coolant or brake fluid in it, if you do not properly maintain it, it will die.(At my shop a fellow mechanic co-worker bragged of how inexpensive it was to repair his honda, where as my bmw cost more, but at the end of the year were even, because he had more maintenance than I did, but parts cost more for me)...yes it takes special synthetic fluid for alot of it... who is installing the engine? I would love to be able to far as checking sensors, there are schematics (maps/diagrams) of every single sensor computer and wire in the car, labeled with certain resistances and volts and ohms each part should safely run on, and when it is broken, you can OHM out the sensor on the correct pins, and know instantly whether it is good or not with out buying any parts. Rebuilt engines are used engines that had an unknown amount of problems, and someone took the time to replace all the parts that were wrong.. still used, but has atleast one new/newly used part on it. I suggest replace it with the one you have, and KEEP the engine you took out, always keep it. when you buy another one, they may charge a "core" fee, but it is way less than you could get if you rebuild the one you have, and either keep it as a spare, or sell it as around, junk yards, LKQ...hope i helped good luck.

4 out of 4 people think this is helpful.

The advice you're getting is mostly pretty good. I would just emphasize what's already been said. BMWs are particular; the cooling systems are something that do need periodic service (fan belt, water pump, thermostat, and often times, around 100 -- 120k miles, a new radiator. And BMW engines don't tolerate overheating at all -- they are much more sensitive to even mild overheating that wouldn't take out an American car motor. You really want to work with either the dealer (although they are expensive) or a shop that specializes in BMWs. The BMW owners club has a magazine called the Roundel -- highly recommended reading for their Q&A section on auto maintenance! Having now scared you, no doubt, you should know that its also true that properly maintained BMWs will last a long time, give you great driving pleasure along the way, and only cost a bit more, on average, than "average" cars. At least this should be the case after you put that replacement motor in! This is a job you really want a BMW specialty shop or the dealer to do, by the way -- a new motor is major surgery!

4 out of 4 people think this is helpful.

Thank you so much for your reply Bill. Unfortunately it won't be the BMW mechanic putting in the engine... The only deals I am getting out of having my car completely die after two months of owning it is having the dealer from whom I bought put in another engine for free (I have to buy the engine of course) or to trade it in and get $1500 for it (which sucks because I know that car, even without an engine, is worth more than that! And I also know the dealer will then put an engine in it and turn around and sell it for like $8000. So he makes all the money and I lose out). He's quoted me an engine for $3400 plus tax. Does this sound reasonable? I have been trying to find engines on my own... but I'm not having much luck since I have the AWD version and I don't want an engine with more mileage than I already have. Anyway, I am still not 100% sure what is going to happen at this point. But if I do have them put the engine in, do you think it is a good idea to take it to the BMW mechanic and have them check it out to make sure everything looks good? Thanks again for everyone's answers! Helps a lot!


What's the mechanics different between bmw 323ci & 323I ??

2 out of 2 people think this is helpful.

Can any one help me please? ???


ci is the designation for a "coupe". i is for a "sedan"

1 out of 1 people think this is helpful.


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