[K9Leader]

I've been losing coolant on my 2010 E91 X-drive, automatic transmission, 138K miles. Water pump and t-stat were done by my indy shop a little over a year ago (it was January and my garage is unheated and I would have been doing it on a QuickJack so I splurged and let the shop do it).

I pulled the belly pan and took a look today - there appear to be two possibilities - at the upper radiator hose where it connects to the radiator and at the radiator drain plug. See pics below:





There are two separate wet spots on the belly pan corresponding to each of these, and it does not appear that the upper hose leak is dribbling down to the drain plug area, so it does appear to be two leaks.

Replacing the upper radiator hose seems easy enough so that is on the list to do. But I have questions about the drain plug area. It appears to be a two-part assembly and RealOEM confirms this:

Control sleeve, P/N 17117521781
Drain plug radiator, 17117530902

Do I replace both or just the plug? Or is this a sign the radiator is about to go or has gone? As far as I know and I can tell, this is the original radiator so it has gone 12 years and 138K miles. Would it be better to just do the radiator instead of throwing parts at it trying to keep it going (albeit the plug and sleeve are inexpensive parts but . . . )?

So, I have come here to the font of E9x knowledge. Please chime in.

[tcphoto]

The drain plug looks dry to me, I would pull the plastic cover off the top of the radiator and see if the small hose is leaking. The BMW radiators are crap, the seam between the plastic and metal is a horrible design. I hope that it’s just the radiator hose or the small hose on top, I just replaced mine two days ago.

[Brian86]

It's the radiator end tank inlet neck. On top. inside the elbow. I can see the chalky residue in the photo. They fail there pretty regularly.

[Daaaaaaaan]

If you're not sure where the leak is, get the dye and UV light and find out for sure before you start replacing every part!

Keep in mind the leak might only happen while the system is pressurized (ie: coolant is hot). And then dry by the time you can really look around things.

Or buy a pressure cap + pump kit off amazon, search for "radiator pressure tester kit bmw" (looks like US$60 will include what you need), pressurize the system on your driveway and find where the drips are coming from. Then sell the kit for $75 locally to someone that can't wait

[K9Leader]

Originally Posted by tcphoto

The drain plug looks dry to me, I would pull the plastic cover off the top of the radiator and see if the small hose is leaking. The BMW radiators are crap, the seam between the plastic and metal is a horrible design. I hope that it’s just the radiator hose or the small hose on top, I just replaced mine two days ago.

The moisture doesn't really show on the drain plug in the pic but it is there. I will probably start with the upper hose and a pressure tester, which would be a good tool to have as I've also got a 2011 E82.

[K9Leader]

Originally Posted by Brian86

It's the radiator end tank inlet neck. On top. inside the elbow. I can see the chalky residue in the photo. They fail there pretty regularly.

Hmm, that means a new radiator is needed, right? The idea of a pressure tester is a good place to start and will be a useful tool to have.

[K9Leader]

Originally Posted by Daaaaaaaan

If you're not sure where the leak is, get the dye and UV light and find out for sure before you start replacing every part!

Keep in mind the leak might only happen while the system is pressurized (ie: coolant is hot). And then dry by the time you can really look around things.

Or buy a pressure cap + pump kit off amazon, search for "radiator pressure tester kit bmw" (looks like US$60 will include what you need), pressurize the system on your driveway and find where the drips are coming from. Then sell the kit for $75 locally to someone that can't wait

Good idea on the pressure tester. I will start with that. It will be a useful tool to have - the E91 is not the only BMW I have.

[DeeDotRayDot]

Hi, new here...I didn't want to post but I cannot find/am finding conflicting information for my radiator and drain plug and hose replacement. My coolant has been dropping without notice the last 2 times I've replaced a hose and I just found out my radiator has a small hairline crack in the upper driver side bend. I can't determine if there is pressure building up and forcing the drain plug out or not. I've had 3 of the drain plugs replaced and I think what is happening is the tabs that hold the drain plug in are breaking when I am turning the black casing in the bottom of the radiator. I was told they are one time use but still haven't figured out if I am inserting them correctly or not. Any help or guidance...and I mean ANY...would be great and appreciated. Should note that I've had a family mechanic replace one, a shop replace the next, and I myself replaced the third. Coolant is $$$ and the unknown is keeping me from having a ride to work. Thanks all! If anyone has a picture of the inside of the bottom of the radiator or a video that shows exactly how to insert the plug and how much to turn it with the 19mm wrench, it would be great.

[jeff.north]

I had a similar issue. A really thin coat of RTV(red) around the plug threads works for a short time however, it did start to leak again. Radiator was actually the cause small crack around the plug housing which would expand when hot and let the plug loosen.

A pressure test helped me find that leak and pinpoint another leak so replacing the radiator was my only option.

The rtv fix was just for a temp fix until the radiator cam in.

[TriumphTim]

Honestly, unless you have records showing otherwise I would replace the radiator and as many coolant hoses as possible.

BMW cooling parts really only seem to last around 100k miles,

You can piecemeal it if needed but once I did everything my car has been great, well except the heater core connection under the dash. Engine bay has been tight.