Member
My 05 325i just had a massive coolant leak. I wasn't driving it at the time but car was parked after driving so engine was hot. Put it in reverse and from what my gf said, it felt like it wasn't running right. Then the car started smoking. When I got there, a huge puddle of coolant had spilled all over the ground and coolant had been sprayed all over the engine bay.
The reservoir tank was practically empty so I assume it must have been a fairly large leak and not a slow drip as this happened out of nowhere. Most of the coolant looked like it had spilled out from underneath the reservoir and after getting it towed, that's where coolant was continuing to slowly leak from.
The entire coolant system was replaced about 2 years ago by dealership (reservoir, thermostat, upper and lower radiator hoses). I didn't notice any cracks on the reservoir but not sure how to diagnose where the leak happened. Assuming it is where the coolant reservoir sits and meets the thermostat below.
Any suggestions?
Member
It’s called an “expansion tank” and it probably cracked. Common occurrence.
Member
The expansion tank (reservoir) was replaced in 2018. Any way to test it to see if the leak is coming from the tank? Was thinking I could run distilled water through it and see if it starts leaking at the bottom.
Member
Nvm. Upon closer inspection under better lighting there's a huge vertical crack in the expansion tank.
Member
Do you have your receipt for the work done by the dealer? I’d definitely go to dealer and have it fix the problem for free. Also, I’m wondering if the part is defective. A dealer expansion tank shouldn’t crack after 2 years.
Member
I put a URO brand expansion tank on my 2004 330i and it failed exactly one year after installation. No more of those!Originally Posted by MarcoZandrini
When I went to replace it, I noticed that BMW had updated the part number on the expansion tank. Speculating that they may have improved the design, and finding no mention of other brands being equivalent to the updated BMW part, I bought a BMW branded expansion tank. That was seven years ago and the BMW tank is still holding.
Member
I didn't own the car when the dealership did those repairs and I believe the shop is a good 30-40 miles from me so I'd have to tow it all the way down there. I bought a REIN replacement part. We'll see how that goes. Didn't wanna spend 60% more for the BMW part
Member
It’s not a reservoir. Reservoirs are simply where reserve coolant is stored, they are not pressurized and not part of the cooling system. Reservoir type systems are also completely free of air.
Expansion tank systems do not have a reserve. The tank is a pressurized part of the cooling system and they have an air pocket in them that expands and contracts as the system pressurizes, and the cap lets air in and out to maintain pressure. This is also why you can’t open them when they’re hot, nor can you add coolant when they’re hot.
You can keep calling it a reservoir all you want but anyone that knows anything about cars is just gonna think you’re an idiot.
Member
OP, the only brand of expansion tank you should buy is Modine. It supplies expansion tanks to BMW.
The installation of aftermarket cooling system parts is strictly verboten.
Jbird
Use only bmw parts and replace the mounting plate and the other small parts with the new expansion tank, does the car have an electric coolant fan behind the radiator or a fan clutch attached to the water pump
Member
I remember going through like 3 expansion tanks.
Make sure to bleed all the air pockets.
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