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Discussion Starter · #1 ·
Hi all,

I'm running around trying to diagnose my e46 325i touring manual with an overheating and disappearing coolant issue. Car has 205,000 miles.

In 2019 around 180,000 miles, I replaced the entire cooling system (hoses, sensors, thermostat, water pump, expansion tank, etc), bar the radiator. Everything was OE or OEM replacement. Car has been super solid since.

Recently at my oil change, the guys said coolant was low but they didn't have any more.
The next day I get some drive through food and pull out hard, revving to like 6k. I look down a mile or two later and my temp gauge is in the red. It was dark and raining so I finished the quarter/half mile back home and turned it off right away.

I've always vigilantly watched the gauge and never seen it move past dead center. I know I was supposed to pull over immediately, and I did so as soon as I could safely.

I refilled coolant and drive a few miles the next day and it overheated again. This time, I shut it off again as soon as I could. It hit the red and I got it towed home.

So, things I've done/noticed:
  • Coolant refilled and system bled multiple times.
  • Rented a cooling pressure test kit and it held 9psi no problem. No audible leaks or bubbles spotted.
  • Unplugged lower radiator fan switch to trigger fan to be on full and it didn't help - still climbed past 110 Celsius
  • No coolant in oil (recent oil change was 2 days before first overheat)
  • Car will idle in the driveway for 20+ mins but eventually start to overheat. If I drive it, it'll overheat in like a mile or less.
  • Seemingly no heat coming out even when engine is warm
  • Noticed light white smoke coming from exhaust at idle and when revving, even when warm. Filmed a video of that here. It's hard to see, but you'll notice it for sure. E46 overheating and white smoke
My logical next steps I think are replace water pump and/or thermostat again, but I'm concerned by the white smoke.

Do I have a cracked head?
 

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2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
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You've been doing some very good work here. Well done.

Do I have a cracked head?
Get one of those kits that detects engine gases in the radiator. That is the best way to answer your question.

The overheating sounds like a lack of fluid cycling through the engine. With a hot engine at idle, does the top hose feel really hot and the bottom hose cold? If so, then your idea of changing the pump and thermostat would be a good one.
 

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Discussion Starter · #3 ·
Get one of those kits that detects engine gases in the radiator. That is the best way to answer your question.
Ok will do! Is that something I buy or can I rent from the auto parts store?


With a hot engine at idle, does the top hose feel really hot and the bottom hose cold? If so, then your idea of changing the pump and thermostat would be a good one.
I will give that a go and report back.
 

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I refilled coolant and drive a few miles the next day and it overheated again. This time, I shut it off again as soon as I could. It hit the red and I got it towed home.
Geeze, it was overheated the day before, and after adding coolant and you let it got to the red zone again and needed the tow truck? Couldn't you just driving up and down the street around the house just in case? I mean you already knew the issue, and let the gauge got to red again?
Unplugged lower radiator fan switch to trigger fan to be on full and it didn't help - still climbed past 110 Celsius
The fan won't help if the radiator doesn't have coolant flow. Get the engine to operating temp, then grasp the radiator lower hose tightly in your hand; if you don't cry in 40sec then no coolant flow through the rad. Bad bleeding job.
 

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Mystery Coolant Disappearing and Overheating
What mystery? When was the last time you checked the coolant in the tank?
Recently at my oil change, the guys said coolant was low but they didn't have any more.
The next day I get some drive through food and pull out hard, revving to like 6k. I look down a mile or two later and my temp gauge is in the red.
This is no mystery: was told it needed coolant; ignored and drove it hard then overheated. I shake my head.
 

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As you know these engines don't take an overheat, even a brief one , very well.

you greatly increased the risk of a head gasket /warped head b driving your car the quarter to half mile home while in the red...

Before you replace any parts you need to test for head failure AND find the source of your leak.. BTW - a pressure test at 9psi does nothing...the M54 cooling system runs at 18-20psi...

I would do the following:
  • compression test
  • swab each cylinder for coolant...run the car up to temp, shut it off let it sit overnight, pull plugs and swab each cylinder
  • Maybe get a UV coolant test kit - dye, UV light, glasses - you might be able to borrow at Autozone.

Right now, I think you have an air pocket in the cooling system..keep bleeding...then do the steps above..
 

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Discussion Starter · #10 ·
With a hot engine at idle, does the top hose feel really hot and the bottom hose cold? If so, then your idea of changing the pump and thermostat would be a good one.
The report on the hand temp check is that the upper hose is hot and the lower one is cold.


Does the electric radiator fan run when the engine heats up?
No it does not, that's why I unplugged the sensor just to be sure it worked.

As you know these engines don't take an overheat, even a brief one , very well.

Right now, I think you have an air pocket in the cooling system..keep bleeding...then do the steps above..
Thanks for your help. I have a leak down kit I gotta get back from a friend and then will give that a go.
 

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Discussion Starter · #11 ·
Before you replace any parts you need to test for head failure AND find the source of your leak.. BTW - a pressure test at 9psi does nothing...the M54 cooling system runs at 18-20psi...
I forgot to mention I re-did that test and pushed it up to 18psi. The gauge immediately starts decreasing, but slows as it gets closer to around the 9psi mark, where it will then hold around the 9-10psi mark.

It's hard to say if I'm getting a reliable reading, but I tried it quite a few times and got this same result.
 

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I forgot to mention I re-did that test and pushed it up to 18psi. The gauge immediately starts decreasing, but slows as it gets closer to around the 9psi mark, where it will then hold around the 9-10psi mark.

It's hard to say if I'm getting a reliable reading, but I tried it quite a few times and got this same result.
well you definitely have a leak..it should hold 18psi
 

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2002 330i auto
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I forgot to mention I re-did that test and pushed it up to 18psi. The gauge immediately starts decreasing, but slows as it gets closer to around the 9psi mark, where it will then hold around the 9-10psi mark.

It's hard to say if I'm getting a reliable reading, but I tried it quite a few times and got this same result.

Now look for the coolant the air displaced, probably in a cylinder.
 

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Can I drain the system and start over? Will that make the bleeding process easier?
No need to drain. Read through this bleeding to understand it, then give it a try.
Post #13 of this thread:
 

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2005 330i manual transmission performance package
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The cooling system is sort of self-bleeding - the air bubbles trapped inside circulate with the flow while the engine is running and eventually get trapped inside the expansion tank. Thus, I think eliminating the circulating air before driving the car isn't worth my time - I just check the coolant level and top off if needed on the next day, after the engine has cooled down.
It is more important to look for leaks and to pay attention to the engine temperature.

On the other hand, if there is a lot of air trapped somewhere inside, it may obstruct the flow in a narrow cooling passage, which isn't good, but fiddling with the upper radiator hose bleeder screw while the engine is running isn't going to magically free the obstructed passage - if anything is going to help, it would be moving the car and revving the engine.

In my experience, properly following the procedure to fill up the cooling system as described by BMW and in the Mango link above rarely results in trapped air. Don't think this should be called bleeding as the sole role of the open screw is to ensure the upper rad hose has been filled with coolant.
It also helps if the front of the car is raised, and the coolant is poured in slowly.
 

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Discussion Starter · #20 ·
No need to drain. Read through this bleeding to understand it, then give it a try.
Post #13 of this thread:
Thanks! I will try this asap
 
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