Coolant connection fitting question
 

I have a 2005 3.0i and have a leak where the bottom of the expansion tank meets this connection fitting (see attached pic, part #3).

I replaced the expansion tank last year and it included the oring that 'snapped' onto the fitting, so I'm not really sure why it started leaking here. It feels like it is no longer snapped into place and can be easily moved in and out of the bottom of the tank opening and won't snap back into a locked position.

Do you think this fitting can be replaced without removing the expansion tank?

No pic. Which motor?

The bottom of reservoir on m54 is the thermostat for the transmission cooler. That part usually self destructs on removal so should have been replaced with the reservoir.

You can get just that thermostat and replace just it if that will replace the wonky connection.

Sorry, didn't attach earlier! Pic is up now, and I added another one here. I have the 3.0.

Thermostat was changed when the reservoir was changed, as removing it destroyed the old one, as you mentioned.

If you can't get it to snap back in...I don't think you have a choice but to pull it and the expansion tank out and apart and see why it's leaking.

A new o-ring may seal it. I keep a spare fitting in my back up parts box. My coolant leak was the lower oil cooler seal. The cooler would teeter due to vibration. Once I secured the transmission lines from moving too much, the leak stopped. Try securing the hose line a bit to limit movement. Or did it crack?

Did you get the tank all the way on?

I used aftermarket part and it took my entire body weight to get the thing to seat. If all you need to do is re-seat you can pull it up a bit and have a new go at it. You will just spill a couple oz. of coolant.

You could use a ratchet strap to help pull it down. Do you recall if the retention spring clicked?

Great question. I thought I got the tank on fully because I replaced it a year ago and no leaks until now. However, I never heard the "click" sound that I expected and I was muscle-ing the crap out of it to try and do so. I just kept pushing until I felt a very subtle "snap" if that makes sense. Do you think it's possible it never really seated completely and I've just been lucky for this long? The tank I bought was a Nissens brand from FCP. I replaced that, the auto trans cooler seals, the thermostat, and all the hoses at the same time.

Pretty sure the tank isn't cracked as it's a year old... I did replace the cooler seals when I did the job and those are not leaking. The leak clearly is coming from where the tank opening meets that fitting and is made worse by wiggling that connection.

Just following up here. Took everything apart and all parts were intact. Leak was coming from the somewhat loose connection where the hose connection fitting (#3 in the diagram) connects to the bottom of the expansion tank. I replaced the o-ring inside the tank where that part snaps in and now that connection is way more secure. Pressure test was successful and I've been driving it around without any leaking. Happy I didn't need to purchase any parts this time around.

[emoji106]
Good job,although I have that mine seems to do things just to screw me over so I'd be careful saying you didn't need to buy parts anywhere where your e53 can hear it...[emoji1787]

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