E60 535xi coolant leak under passenger wheel well
 

Hey everyone, first post. I've got a coolant leak that's leaving a small puddle just in front of my passenger tire, and it seems as though coolant has splashed onto the wheel well liner as well. When it is leaking, the only place I see drips coming from is the "slotted" splash guard that's on the outer edge of the large underbody splash guard. The leak doesn't happen when the car has been sitting, only after I've been driving for a few miles. Also it is sporadic. There's been times in the middle of the day (80 degree air temps) I'll park and come out a few minutes later to see a few drops of coolant on the ground, and others where it's a cool morning and there's a decent puddle underneath.

I attempted to change the expansion tank because the red bobber is broken, but the Dorman part I got at autozone didn't allow the lower hose to attach with the quick clips, so I've got to get a different brand.

My question is whether or not there can be something else leaking that far out on the passenger side other than the expansion tank? It seems like it's too far to the periphery for it to involve the radiator or hoses, and the radiator hoses look fine. The hoses to the expansion tank are good, and I couldn't see any visible cracks on my current one. This all started after my upper radiator hose blew and I replaced it. Could I have overfilled the system with coolant due to not having the bobber functional? I've not gotten a low coolant light in this whole ordeal, but I've added a small amount of coolant every couple days just for safe measure. I'm going to look into it further this weekend, but I guess I'm just looking for piece of mind that this can be a DIY job with my limited mechanical skills. I recently moved across the country and haven't found an independent shop yet. I refuse to go to the dealership.

Thanks in advance!

This is a picture I took the day I figured it out. Pretty hard to see anything but it's all I've got right now. That's the worst it's ever been and fluctuates between that and a spot the size of a hockey puck.

I had the same problem this winter. Mine was a cracked radiator and a bad coolant temp sensor. Wiggle around the temp sensor and see if there is a coolant leak (most of the time when you cant find the leak its the O ring on the sensor that wears over time ($1.00) or you can change the sensor it comes with the O ring ($25). Here's a link so you can see some pics and how to change it. BMW E60 5-Series Radiator Temperature Sensor Replacement (2003-2010) - Pelican Parts Technical Article


Hope this helps.

Thank you for the reply! If that were the issue would you be able to see coolant on the lower radiator hose around the sensor? All of the main radiator hoses are dry. I will try to find time today to investigate that temp sensor as the source. Thanks again!

I'd think you would see some sort of leakage around it. Something similar to figure 1 in the article linked above. Inspect it closely. Take a look at this article: BMW E60 5-Series Cooling System Leak Test (2003-2010) - Pelican Parts Technical Article. Figure 4 tells you some areas to inspect. If you're having a hard time locating the leak that article goes over how you can pressure test the system. Let us know what you find.

There's a transmission cooler tucked right in front of the passenger wheel. And this car is a nightmare spaghetti monster of coolant hoses. Ask me how I know.

RealOEM.com - Online BMW Parts Catalog

Hoses 11 and 12 attach to it.

replace the radiator couple days ago due to a small crack, pretty easy job, some hoses might be quite tight cuz age. be gentle to the hose if u planning change the radiator.

" I've added a small amount of coolant every couple days just for safe measure". Since the bobbler in the expansion tank is missing, you may have over-filled the tank every couple of days, causing the excess coolant to be expelled when the engine is hot. The normal level of the coolant when cold is at least 2" - 3" below the cap, so make sure you don't overfill. Best to replace the tank ASAP.

I finally got time to lift the car and take the splash shield off. I had to let the car run for at least 20 minutes before it would start leaking and it is in fact the expansion tank. With all the little splash shields that come together in the wheel well, it was riding down the different plates making it look like I had multiple leaks. I was able to get a light and my wife's selfie stick up there with my phone and it's leaking from the bottom of the tank where it plugs into the frame. I just ordered a new Behr expansion tank. There are a crap load of coolant hoses in there, I'm glad it wasn't one of them.

I'm chasing this now, either my expansion tank is cracked or the fitting for the sensor at the bottom of the expansion tank is leaking. Two screws on mounting brackets on top of tank are easy to remove, upper hose came apart easily (I replaced upper hose assembly a couple months ago), but I'm having a heck of a time with the larger hose coming from the base of the tank. I pulled the wire clip completely off to insure that it wasn't hooked on, and I'm carefully using large adjustable pliers with curved teeth to gently try to pry and pull that hose fitting off, to no avail.
Any tips?