06 550i

A little over a month ago my 'low coolant level' warning came on. I promptly went to my indy shop they opened the reservoir and confirmed that my coolant level was indeed low. (first time this has ever happened).

They top off the coolant, did a pressure test to see if there were any leaks (found none), and sent me on my way.

Two days ago the 'low coolant level' warning comes on again. I check the coolant reservoir and it is again almost empty.

I have no liquid leakeage on my garage floor and have never noticed anything dripping from my engine. Today I take the car back in the shop and they cannot find a leak anywhere.

Where is my coolant going?

 

Check around the coolant tank. A lot of people on here say that the tanks always get a crack or leak around them.

 

the tank as well as the hose that connects to the bottom of the radiator and has the temperature sensor connection built into it. If it is the hose, replace both the hose and the sensor.

 

Also check your lower radiator hose to the left of the radiator; there you will find a coolant temperature sensor. I had a very slow leak right at that sensor and because I have the undercarriage covers (sports pkg) I had no visible leak in my garage. Coolant just quickly evaporated due to engine heat. Good luck

 

I just replaced my expansion tank... I wondered for a while how I was losing coolant. I think it was leaking very slowly under the tank under pressure only and was burning off prior to hitting the ground... It eventually got worse and starting leaving puddles everywhere. It was an easy DIY fix. I have heard around 80k miles they go - like clockwork my car had just hit the 80k mark...

 

+ to all .. had my hoses and tank done

 

my slow leak turned out to be the thermostat gasket, it was just off the groove in one spot. likely not your problem, but a spot to look if you have things apart/drained.

 

Expansion tank it was. Exactly where you said it would be. I am just about to the 70k mark, spot on.

 

 

Had the same problem on my 04 525i, could never see fluid but could always smell a hint of the coolant. The smell was stronger near the themostat housing and pump area, so I decided to get both changed out. Took it to the stealer and they without hesitation said $1500, the local repair shop wanted $850, neither was in my budget. I decided to DIY and found the pump new for $50 and thermostat new for $60 and coolant for $20...the job was super easy and only took 1 1/2 hours start to finish. You have to remove the radiator top cover with a torx bit, then the inner plastic cover which get you to the electric fan. disconnect the harness to fan and pull fan up slowly, on the right side you can fold the fan bracket to clear the radiator and set aside. This will give you plenty room to loosen the 10mm bolts on water pump, but do not remove till you take the belt of it. Then remove pulley, and the 4 10mm bolts holding pump to the engine (pump will come out with a little pull), remove the clips locking radiator hose to thermostat housing and pull off. Remove bolts to thermostat and unit should come off with ease. After examing the thermostat backside noticed the rubber gasket was broken at the bottom causing the coolant leak, gasket sold for $7. Overall spent $80 and a few hours and the problem was solved, don't see how they came up with a $800-$1500 quote for such an easy job utilizing the simplest tools.