Pegasusxi

Hey guys, I have had a coolant leak that I could not ever visualize from under the hood.
Attempting to find a visual, I took off the belly pan, and anything impeding vision to the turbos(except downpipes/subframe).

When I was able to find some visuals on the turbos, I saw white coolant tracks coming out of an o2 sensor, as well was coolant coming from the top of the turbos at the level of the exhaust manifold.

I just fixed an oil filter housing gasket, hoping it would solve mixing issues. Took it for a test drive, after 20 minutes it leaked loads out in that same area.

I might attempt to remove the downpipes and take out the turbos. I know this is a serious task, especially with the x-drive. I have prepared the subframe to be dropped.

Need help establishing a diagnosis.
My main questions: have the turbos failed? has a turbo gasket/seal failed? Do I have an internal leak? (didnt know about combustion testing until i got it in my garage and started taking parts off.)

Where is the 535xi bleeder screw?
Where does our expansion tank overflow too?

Thanks,
PegasusXi

audiophool

Turbos are water cooled, but I don't think there's any way for them to leak - just the piping from the block. RealOEM.com - Online BMW Parts Catalog

Don't forget: there's an electric water pump and thermostat under the front turbo. Any number of hose connections to those parts could be leaking too.

There's no bleed screw on these. You run the electric pump on a purge cycle:
535: With the key inserted into the dash, no brake pedal, press the start button
Turn the driver and passenger air temp controls up to max temp
Press the defrost button to turn it on
Manually adjust the fan speed to the slowest setting (not off)
then hold the gas pedal down all the way for 10 seconds.

You will hear it cycle. It will sound like a muffled electric drill with water going through pipes.

Pegasusxi

okay. I've ran the electronic purge before. I did it one last time to see if I could then go in for a view, results weren't worthy of diagnosis.

Thank you for your informative response.

I have considered thermostat or water pump failure secondary to the gasket failing, however my car never over heated, or at least never told me per dash coolant temp from hidden odo-menu. got up and stayed around 105C - 110C.
I guess I need more clues to a diagnosis, it never stopped me for over heating and Low coolant after about 20mi.

Is it against BMW 'regulation' to add highlighter florescence to the system for a UV test? [debatable]
If not, I want to track where the coolant is coming from, the white coolant tracks from the exhaust manifold is making me suspicious of internal leak. -> combustion test. boy I hope this ones a negative.
UV test will tell me if this this old from my oil filter housing gasket/ oil cooler gasket, or water pump.

second thoughts anyone?

seanjordan20

You can add you own dye if you want to be sure. They have it at Auto zone and Advance auto

audiophool

Closer look at the turbo coolant lines and they're all o-ring seals. Each pipe does have a section of rubber tubing though, and some parts have heat shielding covering the rubber tubing.

Pegasusxi

If I want a better view of this, it will be after my subframe is dropped. I am going to attempt this on jack stands after the fluorescence test. Any part to be aware of getting snagged while lowering the subframe?
This will be my first time separating the subframe
I noticed the 535xi has engine mounts in weird places. One is a nut, and the other is a bolt that needs to be removed.
Do you agree on this?

audiophool

Dropping the subframe is a lot of work for sure. Know that dropping the subframe requires you to suspend the engine from a bridge fixture across the strut towers. I'd want to be very certain it was warranted before going that far, but it's your car and your call.

In post #1 you mention changing the OFHG hoping it would solve a "mixing problem". Were you getting oil in the coolant or coolant in the oil? You say it "leaked loads" after your 20 minute test drive but you didn't lose enough to trigger low coolant. How much is "loads"? Sounds to me you're concerned you may have a failed head gasket. In post #3 you mention the engine hasn't overheated though.

Is the car currently in a running condition? If it is, and if it were my car, I'd put some test dye in the cooling system. Then I'd go rent a good scope camera and a UV light and try and find the leak that way.

Pegasusxi

Have you dropped the subframe with an engine support?

After the 20 minute drive, low coolant did appear on dash. I am suspicious of a failed thermostat.
I think different driving conditions allowed for both directions to occur, I suspected to be oil scorring/ smelted plastic in a coolant hose.
Oil leve per dash was always max, oil pressure never got high though. Again this is speculation.. I agree UV dye is my next step. I just got a scope for this purpose, great idea.

I am novice, but interested in learning. Underwent desired depth of research, however the x-drive complicates things.

[separate issue]
Oil leaking from what seems to be oil pan area, so i want to also diagnose this, and address it accordingly. I will get some pictures next time I get under there.

audiophool

I've never had to drop my subframe, but an engine bridge/support is needed as you'll be taking away the engine's support. This should be a last resort IMO.

No idea what you mean about "oil scorring/ smelted plastic in a coolant hose". Care to elaborate?

If you've already changed your OFHG, chances are that solved your leak and you're looking at residue. Always look up, wayyyy up, when chasing leaks - gravity you know.

Pegasusxi

Here is a picture of my UV test findings.
https://imgur.com/a/TwTrrMM

NOTE: check out the old coolant white tracking from exhaust manifold in the background.
Thermostat/water pump in good shape apparently. [I wish I had maintenance records from previous owner]

plan of action: drop the subframe and get a better look, replace cooling return line for cylinders 4-6 turbo

Here is a picture of what I replaced during the oil filter housing gasket/oil cooler gasket. The "oil scorring/plastic smelting."
https://imgur.com/a/fE5iRZf