E46 - Mystery Coolant Leak

[mattburley]

Hi everyone, I have a mystery coolant leak in my 325ci. I noticed a coolant leak so booked the car into the garage. After being topped up yesterday before going into the garage, they couldn't find any sign of a leak despite driving the car and spending the day testing it. I set off this morning with a full coolant tank but after the 15 mile journey, I left the car for a few hours and came back to what's in the videos linked below. I checked the coolant and it was again empty. I've checked what I can with my limited knowledge and can see a pool of water in the tray to the left of the engine next to the o/s suspension.

Has anyone have any experience of this or has any idea what's going on here?

Thanks to anyone who can help in any way!

https://www.youtube.com/shorts/GC-ChPLXCbg

https://www.youtube.com/shorts/WJCpQUA2xng

[bmwdirtracer]

Sure; I've got lots of experience with E46 coolant leaks...obviously your chosen shop does not. You can't diagnose this leak by what drips out of the undertray. The car needs to be put on a lift, the undertray removed, and the cooling system pressurized to 15-17 psi...then see where the leak's coming from -- looking from underneath the car.

Realistically, your entire cooling system is due for its third replacement, complete. Radiator, expansion tank, all the hoses, water pump, thermostat, the expansion tank mounting plate, the two plastic pipes under the intake manifold. By far, the most common cause of engine destruction in E46's is cooling system failure.

Find a real shop that specializes in BMWs.

[MIKYZZ4]

Chris just explained what's going on here.

But if you are going to attempt any DIY, start by removing the drip tray,
so you can at least SEE where the leak is coming from!!

[shadowpuck]

agreed - this should be a relatively easy diag if its running through that much coolant.....

as miky says - it might not even be necessary to pressure test it given the apparent size of the leak.....
and, as chris says - at this point you are due for a cooling system overhaul unless that's been done recently...

[bmwdirtracer]

The reason I highly recommend the pressure test is because once an area's that wet, it's hard to tell where the leak begins. On the driver's side, right there are the expansion tank, are half a dozen possible culprits: the expansion tank, the radiator header tank, the top hose, the mounting plate for the expansion tank, one or two heater hoses...you know the usual mess. On the passenger side, you've got the lower hose, the fan switch, the other radiator header tank...and in the middle, the thermostat, water pump, inner ends of both hoses, the two plastic pipes...

...and all of them drop their coolant into that belly pan.

[shadowpuck]

The reason I highly recommend the pressure test is because once an area's that wet, it's hard to tell where the leak begins. On the driver's side, right there are the expansion tank, are half a dozen possible culprits: the expansion tank, the radiator header tank, the top hose, the mounting plate for the expansion tank, one or two heater hoses...you know the usual mess. On the passenger side, you've got the lower hose, the fan switch, the other radiator header tank...and in the middle, the thermostat, water pump, inner ends of both hoses, the two plastic pipes...

...and all of them drop their coolant into that belly pan.

agreed! yeah, for a shop it's so easy to pressurize and test the system. surprised that didn't happen here yet...

[marcva]

agreed! yeah, for a shop it's so easy to pressurize and test the system. surprised that didn't happen here yet...

Though it doesn't sound like you've got the visibility, Coolant leaves a white crust when it dries in the engine bay. Looking for a telltale pattern of residue cen reinforce things. I had a pinhole so fine on my reservoir, I could barely see the stream under pressure, but the stains on the engine bay told me where to look.