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Mystery Coolant Disappearing and Overheating

2K views 47 replies 13 participants last post by  Sapote 
#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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#2 ·
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.
 
#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.
 
#6 ·
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.
 
#7 · (Edited)
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.
 
#9 ·
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..
 
#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.
 
#18 ·
No need to drain. Read through this bleeding to understand it, then give it a try.
Post #13 of this thread:
 
#19 ·
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.
 
#25 ·
Thus, I think eliminating the circulating air before driving the car isn't worth my time -
What?
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.
So before the air pockets eventually are trapped in the tank, how did you drive to places without overheating the air head, or just let it resting in the garage?
It is more important to look for leaks and to pay attention to the engine temperature.
So no bleeding air is needed, and then when the temp gauge moving toward the red zone, then shut it off and pray the GOD?
 
#21 ·
OP, inexplicable coolant loss and engine running hot could be a bad sign.

Do repeat the pressure test, and if you still can't find an external leak, remove the spark plugs and look inside the cylinders.
Visually inspecting the oil isn't a good way to make sure it isn't contaminated with coolant - ask me how I know.
 
#22 ·
I've run into bleeding issues before that resulted in problems until the system was bleed cleanly but they wouldn't have resulted in the problems you seem to be experiencing. Since your system doesn't seem to be holding pressure you need to find out why it's leaking. I have a water pump fail a couple of months after install with a genuine part. It was seeping from the weep hole. I didn't run a pressure test so cannot tell you if it would have showed up but I bet it would have.
 
#24 ·
Wow, just got out the car after my test and discovered some new delicious coolant on the ground. It’s not a constant leak but it’s a decent bit of it.

Did maybe my radiator pop? It’s coming from the drivers side near the expansion tank, but there’s drips of fluid all over the place under the car. It’s on the sway bar, the expansion tank has stuff all over the side. Cant quite narrow it down.

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#29 ·
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?
Sounds like your car was working fine from 2019 until a few days ago. I'm going to assume that prior to what you just described, you did not have overheating problems or lack of cabin heat (do let us know if this is not true). If that's the case, it's not a case of bad bleeding because if it was bad bleeding, then you would've noticed all sorts of problems over the last 3 years. The fact that your cooling system can only hold 9 psi and now you have a pool of coolant on the ground, something broke and you're the best person to go find what broke. While we're on this subject, Bentley manual spec's 1.5 bar as the test pressure for the radiator and the common BMW expansion tank cap is rated at 2 bar. As such, we can speculate that the cooling system pressure when hot is approx. 1-1.5 bar. Keep this in mind when you're pressure testing. 1.5 bar = ~ 21 psi so the previously suggested 18 psi test is right on target. Unfortunately your cooling system did not hold that pressure for long......

Wow, just got out the car after my test and discovered some new delicious coolant on the ground. It’s not a constant leak but it’s a decent bit of it.

Did maybe my radiator pop? It’s coming from the drivers side near the expansion tank, but there’s drips of fluid all over the place under the car. It’s on the sway bar, the expansion tank has stuff all over the side. Cant quite narrow it down.
Based on this description, I would concentrate your investigation on the radiator and the hard coolant pipes under the intake manifold.
 
#39 ·
Ok, got a bit more info to add here. I think I've narrowed it down to head gasket or cracked head.

Pulled the plugs and this is what they looked like. All plugs and coil packs were replaced less than 2,000 miles ago in September.
It's cyl 1 from left to cyl 6 on right.
Note the cylinder 3 plug is a lot cleaner looking.

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I ran a leak down test today and most cylinders have a little bit of air leaking from the oil cap.
Cylinder 2 leaks a ton of air into cylinder 3. My gauge isn't reading properly, so I don't know percentage but it is very audibly leaking and you can feel it clearly.
I double, triple checked I was on the correct stroke.

This is why I think the condition of spark plug 3 is noteworthy. Is the head gasket bad between those cylinders there and there's mixing between the two cylinders?

The other thing I failed to mention in the original post as it didn't seem relevant at the time was that I had a misfire code a few months ago.
It was in late September and it was resolved by replacing all the coil packs and spark plugs. (done less than 2000 miles ago as previously mentioned).

Was this possibly related or just coincidence?
 
#41 ·
I ran a leak down test today and most cylinders have a little bit of air leaking from the oil cap.
This is normal as blowby gas past the piston rings into the crankcase.
Cylinder 2 leaks a ton of air into cylinder 3.
This is the big problem: with #2 valves all closed, the only way to leak into #3 is through the head gasket, which means the head bolts were pulled off the block threads. It's time for Timesert the block head bolt holes.
It was in late September and it was resolved by replacing all the coil packs and spark plugs. (done less than 2000 miles ago as previously mentioned).
not related to the current problem.
 
#43 ·
Just wanted to post a follow up that the mystery has been solved.

I tore into the engine and found the water pump destroyed. I ordered this from FCP Euro in April 2019 and I put maybe 30,000 miles on it since then.
Kinda crazy this plastic impeller version failed like this.

I'll be ordering the metal version from EMP Stewart despite the lifetime replacement from FCP.

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Thanks everyone for your help.
 
#45 ·
Saleri.

Yeah it pretty much does since the water pump failed and the car overheated. Probably warped the head and/or blew the head gasket, so it was burning coolant. One of the first things I mentioned was that I could see white smoke in the exhaust, so I think this is the root cause of all the issues I encountered
 
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