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Thread: E46 Overheating Issue Solved

  1. #1
    Join Date
    Jun 2020
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    2004 BMW 330CI

    E46 Overheating Issue Solved

    I have read without exaggerating about 100 threads about overheating and not one of them stated the exact issue I was having and how I figured out what my problem was. Sorry if this is a long post but want to detail as much as I can.
    To start off I have an automatic 2004 330CI with 230,000 miles on it. About three weeks ago on my way home from work I heard a loud pop, followed by my AC getting warm and car starting to overheat. I got to the red section before I was able to safely pull over and shut my car off. Prior to this issue I had never had an overheating issue and the only non-original part from the cooling system was the thermostat (housing was cracked so replace when I first purchased the car). So all the cooling parts to my knowledge are original and have 230,000 miles on them so my expansion tank blowing up didn’t come as a surprise but more so a lesson that I should have replace everything way sooner.
    I purchased a Dorman expansion tank kit which included the tank, oil cooler thermostat (original didn’t break when removing old tank but replaced anyways), and coolant level sensor. Before filling it up with Zerex G48 coolant I opened the bolt hole in the block itself to make sure I got as much old coolant out as possible. Once topped off I essentially did every technique that I read about to bleed to cooling system:

    • Lift the front end
    • Put the ignition on the ON position with the heater full blast and both tank cap and bleeder screw off
    • With the car running and tank cap off running the car with the heater on full blast
    • Massaging the lower radiator hose to help air pockets get out
    • And one not so common method where you run a vinyl tube from the bleeder hole to the tank opening. Check out the link https://www.youtube.com/watch?v=grUQD9tlDbM
    • After all these I would let the car sit over night and top off in the morning

    After all this my car would overheat when at idle, especially with the AC on. While driving it would cool down but not enough to get the needle back to the middle temp position but as soon as I slowed down the temperature would rise quickly. I know this because I connected a Bluetooth OBD adapter to keep an eye on temps plus the needle itself was moving. I checked which is probably the most common issues for overheating, the clutch fan and electrical fan. Electrical fans came on with the AC and the high and low settings worked just fine, no missing fins. I did the paper test on the clutch fan and it failed miserably. I replaced the clutch fan with a Hayden one (sounds like a diesel truck so I recommend getting the BMW one) and decided to keep the fan blades, I know risky. This made a huge improvement, but car would still do the same thing just take a little longer to overheat since it had proper fan assistance now and I could even drop it into neutral and rev the motor to get more air to blow.
    Continued to do more research and started to think maybe my water pump was starting to go bad so I tested it according to what I read. From the posts that I read if you pop open the tank cap and see a stream of coolant shooting across the inside of the tank your pump is fine. And if you rev the motor the stream would get stronger. Even though mine did have that stream and got stronger as the rpm went up, I decided to replace my water pump with a metal propeller one (AC Delco), aluminum water pump pulley (URO Parts), and coolant temp sensor (Dade). Installed everything did the same bleeding procedure and made no progress. Same issues persisted. There were absolutely zero coolant leaks, I highly doubt there was air in the system, and coolant temp sensor worked properly. I know the hoses, yes though old, they were not brittle and looked good plus they didn’t leak.
    I was sure that I had a cracked head at this point. Since I had no leaks, I doubt the head gasket was bad, so I figured I had a hairline crack in my head letting combustion gases into the coolant and overheating it. Knew that it wasn’t a big crack because I wasn’t loosing any coolant. I did a block test with the blue liquid but it never changed color. Did it when cold and at operating temp and still no color change. WTF!!!
    I kept reading about what people replace and what resolved their issue and why they think it is, and only thing left to replace were my hoses, the radiator, coolant temp sensor that is inside the block and the thermostat. I decided to try the thermostat first since it was the easiest part to replace. I had already done the warm up test, where if your car takes very long to warm up the thermostat is stuck open or if it overheats quickly it’s stuck close. Though mine would overheat no thread ever said that while driving the temps would come down, but wouldn’t you know that is a symptom of a thermostat stuck closed and that is what was causing my overheating issue! Aside from no threads stating, at least the ones I read, that it would cool down when driving, no thread also spoke about the stream of coolant inside the tank. Before replacing my thermostat whenever I would look inside the tank the stream was always shooting. No matter if AC/heater were on or off, car cool or at operating temps, it was always there. Once I replace the thermostat (Mahle) and with the car being cold I started the bleeding process and noticed there was no stream shooting and my heater was on. I rev’d the motor thinking my pump messed up and got stuck and some stream shot across but not like before. I turned off my heater and the stream appeared. I was still well below the temperature at which the thermostat would be completely open (95 Celsius or 203 Fahrenheit). I let car idle till it got to 185 Fahrenheit which is in the range of operating temps and noticed the stream now appeared and my heater was on. After testing the car, letting it cool down, and topping it off my car doesn’t exceed 200 Fahrenheit. This entire time thinking since I replaced the thermostat it couldn’t have gone bad in a year and a half but it did and along with the fan clutch were the causes of my overheating issues after replacing the expansion tank. I know some will say to use original BMW parts and these issues wouldn’t happen and/or I’ll be avoiding any issues in the future but with all this covid19 mess, right now was not the time I wanted to spend on the genuine parts (even though I spent extra on parts I didn’t need and coolant jugs after every part replacement).
    So to make this shorter for those who skipped the entire reading this is how I determined the thermostat was bad and stuck closed

    • Car would over heat at idle, but cool down once driving or if dropped into neutral and rev’d motor to spin clutch fan faster. Water pump, pulley, expansion tank, coolant temp sensor all had been replaced a couple days prior
    • The stream of coolant inside expansion tank should only be shooting if 1) car is at operating temperature no mater if AC or heater is on, 2) under operating temperature and AC/Heater is off

    Hope this helps anyone will the all so common e46 cooling issues

  2. #2
    dworthy's Avatar
    dworthy is offline Wagon meister :) BMW Tech Expert
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    Welcome to the Forum!

    Yes you were way overdue for a cooling overhaul, about 6 years ago.

    Not sure the brand of thermostat you used, but that is typical of after-market parts, they only last for a short time.

    Overheating at idle points toward the clutch fan being bad, do the newspaper test to see if it is locking.
    Darin
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  3. #3
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    The installation of aftermarket cooling system parts is strictly verboten.

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