[dyrus587]

hello guys i have a problem with my 07 335i sedan

for the past 2-3 months i have been refilling coolant every 1-2 weeks. the low coolant light pops on my dash after a week and a half of driving in the city, less freeway. every time i check the reservoir the next morning after the car has cooled off, the coolant stick is all the way down and i can slightly see some coolant left. i usually fill it to the max but same problem occurs a week later.

where i park the car in my garage, there are insignificant amount of drops that can not add up to coolant disappearing every week or so. I wonder if the coolant is evaporating or leaking while i drive?

appreciate all the help i can get. thanks!

[dyrus587]

bump

[TheeGovernor]

Look for leaks in the engine bay. How does the exhaust of your tail pipe look like?

[robthewrench]

It is not evaporating. If you don't see a leak while the car is parked, you most likely have a leak when the system is pressurized by heat and the waterpump. You'll need to do a pressurized test of the cooling system.

[dyrus587]

Originally Posted by robthewrench

It is not evaporating. If you don't see a leak while the car is parked, you most likely have a leak when the system is pressurized by heat and the waterpump. You'll need to do a pressurized test of the cooling system.

is there a way i can do a DIY of this? would prefer to try and fix it myself first before spending money at a shop

[robthewrench]

Originally Posted by dyrus587

is there a way i can do a DIY of this? would prefer to try and fix it myself first before spending money at a shop

As a first step you could try and get a good look around the system when it is hot and under pressure. Put the car up on stands or ramps and remove the under tray. Then turn on the car and run it until it reaches operating temperature. Then shut it off. While the car is still hot look are the various hoses, pump, reservoir, connections, etc...for any sort of leak. You may need to run the car on the stands for a decent amount of time to see if you can spot anything dripping.

The hard part about this is that the car is hot! You can easily burn yourself on the exhaust to other components.

You may want to try adding a UV dye to the coolant to help you find the leak. You will need a UV flashlight. This makes it easier to see the leaking coolant.

At an indy shop, they would do the same test, but they will pressuring the cooling system with an air pump instead of running the car. By keeping the car cold, it is way easier to poke around with the flashlight to look for the UV dyed coolant. The pump also contains a pressure gauge that helps the shop understand if the coolant system is holding pressure or leaking down.

You could buy a coolant pressure test pump and do this yourself. You'll also need an adapter that matches the e-90's cap. However, it is probably easier to pay an indy shop to do it for you.

[dyrus587]

Originally Posted by robthewrench

As a first step you could try and get a good look around the system when it is hot and under pressure. Put the car up on stands or ramps and remove the under tray. Then turn on the car and run it until it reaches operating temperature. Then shut it off. While the car is still hot look are the various hoses, pump, reservoir, connections, etc...for any sort of leak. You may need to run the car on the stands for a decent amount of time to see if you can spot anything dripping.

The hard part about this is that the car is hot! You can easily burn yourself on the exhaust to other components.

You may want to try adding a UV dye to the coolant to help you find the leak. You will need a UV flashlight. This makes it easier to see the leaking coolant.

At an indy shop, they would do the same test, but they will pressuring the cooling system with an air pump instead of running the car. By keeping the car cold, it is way easier to poke around with the flashlight to look for the UV dyed coolant. The pump also contains a pressure gauge that helps the shop understand if the coolant system is holding pressure or leaking down.

You could buy a coolant pressure test pump and do this yourself. You'll also need an adapter that matches the e-90's cap. However, it is probably easier to pay an indy shop to do it for you.

thanks for the write up i appreciate you helping me out since this is probably the only good answer i have received. also, i'm from SoCal so there are lots of specialized shops with higher prices like SSR performance and all those euro tuning shops. do you think it is better to take it to them or an indy shop

[robthewrench]

Originally Posted by dyrus587

thanks for the write up i appreciate you helping me out since this is probably the only good answer i have received. also, i'm from SoCal so there are lots of specialized shops with higher prices like SSR performance and all those euro tuning shops. do you think it is better to take it to them or an indy shop

I would make a couple of phone calls to various shops and describe your problem and see if they suggest doing a pressure test and have them estimate the cost.

You'd like to go to a shop that has some BMW experience, but it doesn't have to be a higher end specialized tuning or performance shop. I would try to find a good indy who is more interested in changing valve cover gaskets than dyno tuning.

[Speedy_12139]

I would bet. My next paycheck (which wouldn't be much anyways)

It's the seam on your expansion tank itself... I had the exact same issue. I would check coolant, and it would always be down a bit. Bit I always caught it before it got super low.

Till I was doing a WOT pull in my 335i one day, and once I was done, a few seconds after. I got a "low coolant" error. Pulled over, opened my hood, and found coolant sprayed out from around the back lip of the expansion tank. Closest to the strut tower. Where the leak wasn't would never have been noticable. Without removing the tank...

I replaced the tank, and cap, which were both super cheap. Ran the bleed procedure twice. And I haven't had the issue since!