[holmesk164]

I'm trying to get to the bottom of a coolant leak on my 335d, every time I go out a drive the expansion tank is always empty when I get back. It doesn't leak unless pressure is in the system.

The leak seems to be coming from underneath the car from what I can see its like directly central under the engine. Ive just done a pressure test and all coolant hoses, radiator and expansion tank/cap seem to be ok. I can't see any obvious signs of coolant running down anywhere or around the engine bay but its all over the ground.

I've changed the flange that goes onto the cylinder head a few weeks ago as I heard this was a common issue.

Any ideas would be grateful, I don't have ramps or stands to get under the car currently.

[335dlci]

Have you pressure tested it?

[lnxguy]

Time to get it up on stands with the engine running and look for a leak. My guess is the tank is split if it's not the coolant flange.

[Asonchadwick]

Is it deleted? If so check the rubber coolant cap. Mine was leaking from there the rubber was failing and I thought it was the water pump but it wasn't. If it isn't deleted then pressure test it for sure!

[lnxguy]

Should have a billet coolant cap! If not, get one.

[DougNBodie]

Heater hoses, Heat exchange, water pump hoses? Mine just did the same think and I ended up replacing just about all the hoses and a new expansion tank. Decided to just pay for this stuff once so I got it at FCP Euro and their lifetime warranty. Good luck.

[Mik325tds]

I had the same problem. A friend told me that the water pumps give up at high mileage, so I replaced it. But that wasn't the problem (although it is a good idea to replace the water pump after around 150k miles). The problem was the connector below the tangential intake ports (see pic). I first ordered a new seal, but it still leaked afterwards. Then I replaced the whole connector 11127806196 and it fixed the leak.

[fearitself165]

Originally Posted by lnxguy

Should have a billet coolant cap! If not, get one.

You're referring to the one from TME is that correct? And if so is that the one that goes on the water pump or the other one on the heater hose?

[fearitself165]

Originally Posted by holmesk164

I'm trying to get to the bottom of a coolant leak on my 335d, every time I go out a drive the expansion tank is always empty when I get back. It doesn't leak unless pressure is in the system.

The leak seems to be coming from underneath the car from what I can see its like directly central under the engine. Ive just done a pressure test and all coolant hoses, radiator and expansion tank/cap seem to be ok. I can't see any obvious signs of coolant running down anywhere or around the engine bay but its all over the ground.

I've changed the flange that goes onto the cylinder head a few weeks ago as I heard this was a common issue.

Any ideas would be grateful, I don't have ramps or stands to get under the car currently.

I know u said you already replaced the cylinder head coolant flange, but did you replace the two o-rings for the hoses that connect to the flange? Idk if you can find them separate without buying the hoses. You can find them on TME that's the only place I know of where you can buy them that is.

[lnxguy]

Originally Posted by fearitself165

You're referring to the one from TME is that correct? And if so is that the one that goes on the water pump or the other one on the heater hose?

Correct, water pump requires the billet cap.