[Andrewiffic]

I have a coolant leak that only occurs once the car is warmed up and I'm driving. After I shut it off I can see that there is coolant dripping from around the waterpump / thermostat area but no longer leaking. Just wondering how I can locate the exact leak? It's an AWD model so there's not a lot of room to see what's happening. I have the undertray off and have the car up on ramps but it's really hard to see since there are about 4 hoses coming to that area as well.

It's a small leak since I've only had to add about 1/2 litre after a 30min drive.

It's a 2007 n54 engine.

Any ideas? Thanks

[StradaRedlands]

A lot of possibilities in that spaghetti bowl of hoses down there! Get a loaner pressure tester, that should help!
https://www.autozone.com/loan-a-tool...ressure-tester
I always suspect the expansion tank, sensor, and bottom coolant hose before the water pump/stat, but it could be any of the above.

Best to get it sorted out before the small leak becomes catastrophic and leaves you stranded.

[Andrewiffic]

Thanks. Was thinking of maybe picking up a Pressure tester. I'm in Canada so no Autozone but I'll see if any place around here rents them.

I had a good look at the expansion tank and it seems totally dry around it so I don't think it's coming from there.

I'll see if I can take a closer look at the bottom coolant hose.

[StradaRedlands]

Originally Posted by Andrewiffic

Thanks. Was thinking of maybe picking up a Pressure tester. I'm in Canada so no Autozone but I'll see if any place around here rents them.

I had a good look at the expansion tank and it seems totally dry around it so I don't think it's coming from there.

I'll see if I can take a closer look at the bottom coolant hose.

Hopefully there is a loaner option in your area... that should really remove a lot of the guesswork! Hope the leak is related to the tank, as that is a LOT easier to deal with! But if you sense it's coming from the pump area, it probably is. Fingers crossed it's the easy way!

[jwalker87]

I had a 4-year-old waterpump on my 2011 335i (so N55, but the coolant system is basically the same as the N54) that started leaking from the plastic housing only when it was warm. Very similar symptoms to what you are describing. I only found it by jacking up the car, removing the plastic bellypan, and then running the car up to normal operating temperature - then it leaked and I could see the steady drip.

If it was coming from the tank, you should see signs of coolant dripping/running down the chassis under it. I have also had that happen on this car, and it was relatively obvious.

I would recommend doing something similar - get as much visual access as you can, then let it run and get hot, then inspect. Otherwise, unless you have recently replaced the water pump and thermostat, then they are prime candidates for leaking like this, and are probably near the end of their lives anyway.