2006 325xi Coolant leak from top of expansion tank.

[sshivaram]

This was posted under E46..oops...mine is an E90.

https://www.bimmerforums.com/forum/s...bly-2006-325xi

Can someone point out what is causing the leak ?

[SlackTube]

Coolant constantly circulates and the system should be thought of as a whole. You obviously have a leak which is probably the expansion tank or the radiator bypass line on top of the radiator as both fail frequently. When you have a leak or an open condition in your cooling system you are not allowing the cooling system to build pressure...
water boils at 212 degrees but under pressure the boiling point goes higher. Same thing for your cooling system. It has roughly 16 psi pressure when hot. Without a sealed system you are not building good pressure and probably boiling your water/coolant.
fix your leak

[sshivaram]

I see the coolant leaking from the top of the expansion tank. It leaks when the coolant temperature drops suddenly from a high of around 105c to around 85c.
Its a new expansion tank.
It has a new cap also.
It only leaks under aggressive driving at a certain range when the coolant temp drops rapidly ( this is when the thermostat closes).

[sshivaram]

Car was in the bmw shop for many weeks. The entire system was pressure tested. The bmw technicians couldn't figure out why the coolant leaks at a certain point from the expansion tank cap. Its designed to hold pressure only to certain extent.

[sshivaram]

Few things:
1. In most cars that have regular water pump, pressure builds up because of the pump which runs continuously, thermostat opens up at around 89F (may be different in cars) and coolant temp is kept at a constant value with a bit of hysteresis.
In the E90, we have electric pump ! The pump is activated by an unnecessary algorithm in the name of making it more efficient put practically i am always going WOT on it throwing the efficient thinking out the window.

My system has been pressure tested and zero leaks. It leaks because of excessive build up in the coolant expansion tank. When the coolant is removed and emptied out from expansion tank, the car is running clean and no more leaks ignoring the low coolant light lol.

[sshivaram]

Will leave this here..

http://www.e90post.com/forums/showthread.php?t=829913

[sshivaram]

the 325xi has 3 moving parts in its cooling system that controls how it works: the electric pump, the electric thermostat, and the coolant temp sensor. This is still not resolved: the leak from the top of the expansion tank. Again: its a new tank with new cap. Somehow, excessive coolant gets into it causing the overflow from this tank.

[Marcus Sky]

This sounds very interesting... I've had some similar dealings with my E39 but not with my E90...

Did you find out and measure exactly how much coolant should be in your system before refilling or topping off every time?

[sshivaram]

This sounds very interesting... I've had some similar dealings with my E39 but not with my E90...

Did you find out and measure exactly how much coolant should be in your system before refilling or topping off every time?

I keep the coolant expansion tank nearly empty. I will fill it up, let it overflow, and remember to keep the airconditioning vents closed because you don't want that coolant smell inside the cabin. So, the car really runs on just one gallon of coolant instead of two. Once the expansion tank is empty, i stop losing the coolant from the top. There is some weird timing issue when the electric pump is still pumping and the thermostat decides to close, i don't know the coolant flow direction yet. Have to debug this.

[Marcus Sky]

I keep the coolant expansion tank nearly empty. I will fill it up, let it overflow, and remember to keep the airconditioning vents closed because you don't want that coolant smell inside the cabin. So, the car really runs on just one gallon of coolant instead of two. Once the expansion tank is empty, i stop losing the coolant from the top. There is some weird timing issue when the electric pump is still pumping and the thermostat decides to close, i don't know the coolant flow direction yet. Have to debug this.

Yeah, it almost sounds like they are out of sync.

[sshivaram]

Yeah, it almost sounds like they are out of sync.

The thermostat is new, and electric pump is new LOL. how to debug and fix this system with just 2 moving parts

[BMWXBMW]

I'm a new member here but I'm hoping that my answer might be useful to someone else in the future in case this problem is fixed by now!...

I had a similar issue where the coolant was leaking from the expansion tank on my 2007 X3 but also the low level coolant lamp was coming on and off on the instrument cluster and the problem was that when the previous owner had the thermostat changed the mechanic either forgot to plugin the electrical connector onto the thermostat or somehow it came loose... After electrical connector was connected to the thermostat the leak from the expansion tank cap stopped immediately and it's been good since then.

[sshivaram]

in my case, i have a new radiator, new coolant expansion tank, new electric coolant pump, and new thermostat.
Still, it blows
Easily repeatable: run car at high (RPM) speeds, the coolant temp rises to around 107C, and drops suddenly to around 70C (all electronically controlled and working accurately) and coolant leaks out of top of the coolant tank profusely. Something obstructs somewhere. Dealers couldn't figure out, and we haven't fixed this for 3-4 years now.

[2000Beem]

I'm new to the forum and bmws and trying to solve this issue, too. I have the same issue with my new e46 - coolant leaks from the top where the expansion tank meets up with the radiator when it cools. I noticed it when I was working on the headlights after turning the car off. lol My thinking is there is a leak and because of it the lowered amount of coolant is getting way too hot and boiling/bubbling. But, why does it leak out from where the expansion tank and radiator meet? I would think that it needs to hold pressure, too. That makes me think that maybe that spot where they meet is part of the problem. Why is it not sealed? Fixing that first - I would think would be my starting point.

Actually, after looking at it again it seems that is not the expansion tank, but part of the radiator (I think). It's the plastic housing that joins to the radiator.

[sshivaram]

I managed to get the BMW GT1 DIS software, and the DME Module shows an "electric coolant pump Fault code (not currently present)".
I managed to bruise my hands; my fingernails are dark and black; head hurts and finally managed to take out the thermostat and
pump. I will order a brand new Pump and lets see what happens. Nothing else appears to be wrong with the car. I was told the Electric
coolant pump is new, but it looks very old. I am unsure if its new. It has several serial numbers on it, is there any way to figure out
what year it was made ?
This is the pump:

Pierburg Pump Technology
Germany
7.02851.20....15...062...00977

Folks, we really should solve this problem. This has been going on for far too long. I want to enjoy my car. Thanks

[sshivaram]

Put in a brand new water pump, same problem ! When the coolant temp is around 97-98, and i floor the gas pedal, the temp starts going up to around 104-105 and then drops down to 80s, and the coolant appears to get under pressure and blows out of cap of the expantion tank. Next step: get a used coolant expansion tank, an entire unit with its own cap and test it.

[sshivaram]

Put in another coolant expansion tank, bought on ebay for $40, and same problem: under extreme load conditions, coolant leaks out of top of expansion tank cap. its designed to leak out from there, and there are over-flow channels and holes.

Next, TODAY, i have done a full back flush on the hoses going into and out of heater core. I disconnected the inlet hose from the radiator top, and the outlet hose of heater core from the bottom, and ran water from a hose through it. I ran water multiple times in both directions. I did see some whitish sand like particles come out.

I filled up the entire system with water and did a bleeding multiple times, ran the car engine at high revs and around the block here. NOW, i have full heat coming in through the vents inside ! This is an amazing step forward. I want to make sure the coolant doesn't leak anymore under pressure. Its holding steady for over 30 minutes now under all load conditions.

[sshivaram]

no good. took it out for a drive and blows cold air, and coolant again leaks from expansion tank cap.

Perhaps, the electrical wiring may be at fault here. It controls how and when the water pump is activated, along with the electrically controlled thermostat:
https://www.bimmerforums.com/forum/s...ooling-problem

[relative4]

Have you tested for a head gasket leak?

[sshivaram]

Never tested for head gasket leaks. That can blow up the coolant system and cause high pressure. But it only happens during certain times, easily reproducible, so doubt if its head gasket leaking.
The DIS software did show a "bus fault" error with the electrical water pump. Does it mean the computer isn't able to talk to the pump correctly.

[sshivaram]

Another lead to follow up: http://wiki.bavariantechnic.com/inde...mp_Malfunction

- - - Updated - - -

This looks promising:
https://www.germanboost.com/showthre...tion-Low-Power

"Melted positive power distribution block in engine bay. Replaced and car runs fine, no codes so far."

[sshivaram]

I plugged in the Foxwell NT510, and cleared all the codes. Took it for a 20 mins drive under normal driving conditions.

The coolant had leaked, and error code was stored in the DME:
2E83 DME Electric coolant pump power-reduced operation.

Looks like wiring harness. Can't be anything else if the DME is unable to communicate correctly with the
electric coolant pump. Next step: Lets take the wiring harness out and check the 4-5 leads from the
pump to the DME.

[batiste23703]

Can somebody please tell me they figured this out. I am having the exact same issue with an E89, N52 engine. Brand new coolant tank, cap, thermostat, and water pump. Still having back pressure through the reservoir cap.

I plugged in the Foxwell NT510, and cleared all the codes. Took it for a 20 mins drive under normal driving conditions.

The coolant had leaked, and error code was stored in the DME:
2E83 DME Electric coolant pump power-reduced operation.

Looks like wiring harness. Can't be anything else if the DME is unable to communicate correctly with the
electric coolant pump. Next step: Lets take the wiring harness out and check the 4-5 leads from the
pump to the DME.

[sshivaram]

Its the wiring harness to the electric coolant pump. The pump is controlled via the CAN bus electronics and a bad wiring harness is causing disruption in the signals sent to the pump.
This problem is very easy to reproduce. You just step on the throttle while cruising at around 30-40mph (in 6th gear, higher gears to reduce speed) at normal operating temps (coolant at around 90C) and in 10 seconds the overflow happens. The pump starts at full speed running the coolant thru the radiator and the thermostat shuts down when it cools while the pump is unable to stop in time. This is my hypothesis.
My mechanic wanted a car badly and he took my 2006 325xi, i don't have the car anymore. I never actually fixed the problem but figured out what the issue was.