[nicky dj]

Guys, I get a coolant level low every week or so and just fill it up with distilled water living in California. But I cannot trace any leak under the car in in engine bay whatsoever. Where is the coolant disappearing to?

[Dave92N54]

Check your oil. Bad OFHG can leak coolant into oil or vice versa.

Otherwise, it HAS to be leaking somewhere.

[Silnismo]

There's definitely a leak somewhere, there are multiple leak prone spots within the E90 cooling system. Even the radiator starts leaking after enough wear and tear.

[tcphoto]

Coolant doesn't just evaporate, you have a leak somewhere and it sounds like it's steady. I'd start looking around the engine, pull the air duct on top of the radiator and look at the small ET hose. If no dried coolant is found, pull the belly pan, look at the pan for coolant and around the water pump, thermostat and radiator. I had the smallest leak from the ET hose and it's been fine since.

[ash6r]

Had the exact same issue and it turned out to be OFHG. Coolant was leaking in to the oil lines. Do a oil change to confirm but pretty sure thats your problem.

[nicky dj]

So a bit of history... I changed all the hoses including the one that runs along the axle, expansion tank, installed a CSF aluminum radiator, etc.

Thanks, i'll check the gaskets.

[KROOKEDking420]

Check ur under tray it's probably a pool by now🤷🏽‍♂️😬👍👌😉😔

[nOshi]

Anytime I do anything with the coolant system I use this tool afterwards to check for leaks. Put some pressure in the system and trace where the leak is.

https://www.harborfreight.com/radiat...kit-63862.html

[GabL750]

Originally Posted by nOshi

Anytime I do anything with the coolant system I use this tool afterwards to check for leaks. Put some pressure in the system and trace where the leak is.

https://www.harborfreight.com/radiat...kit-63862.html

I just bought a 328xi coolant level is a bit low and it seems to be a little bit wet under the intake manifold, what can cause this.

[MadDog89]

Any luck finding the leak? As some have suggested the oil filter housing gasket is known to leak coolant into the oil - you can verify that by doing a used oil analysis, just search for it online or ask around. The OFH gasket over time becomes quite brittle and in some cases the actual oil filter housing becomes corroded if incorrect coolant is used. This creates a passage for oil/coolant to intermix because the two cavities are so close to one another.

There are many other ways to spring a leak with these cars unfortunately. In my experience the original radiator had a pin hole leak. Replaced it with a new one only to find it leak around the same area 2 years later (low driver side). BMW coolant leaves residue to help track the leak, but you'll have to really dig in and pull stuff off to see it. Removing the fan helps and you can run the electric coolant pump without starting the car and see if you find anything (there are tutorials on how to do that). Other than that, there is also a method to pressure test the entire cooling system and look/listen for the leak, but I've never done that. I would also advise against using dyes that glow under black light or whatnot, only because I don't know how the materials making up the coolant system will interact with the solution (going back to the pitting/corrosion issue if using incorrect fluid). Ask any Engineer and they would agree.