Leaking coolant with AC on

[BeLiQ]

Looking for some ideas and where to start troubleshooting.

I have some strange, to me, coolant leak. I was driving the other day for a fair amount of miles with AC blasting. Came back home and as soon as I parked I had a small puddle of coolant. I knew it was leaking cause my roommate told me he had to refill it. He was in charge while I was away for 2 months.

On the next day, I had warning light saying Low Coolant, refilled and proceeded. I took the car for the exact same trip deliberately having the AC off to see what will happen. No leak at all! And hadn't leaked still.

[wgait]

I just went through a similar problem. In my case it was the top radiator bleed screw. It is just about an inch away from the radiator cap on the coolant overflow tank. There is a small washer in the screw that goes bad. If you take the screw out you will be amazed at how small the hole is but after driving it spits out enough coolant because of pressure in the hot system to cause your problem. Bought the $2.95 part from Bav Auto and all was good. Use caution when you screw the old/new bleed screw down - if you go too tight the head of the screw will snap off - it's all plastic, of course. (p. 20-14 in the Bentley manual has a picture of the overflow tank assembly with the screw visible to the right of the radiator cap.)

[theos]

I had similar symptoms...low coolant warning with the AC on. Chances are it has nothing to do with the AC being on. I pressure tested and couldn't find where the leak was coming from. Finally I blew compressed air into the hole by the fill on the expansion tank and PROPERLY bled the system. Haven't had a problem since. If you do a search you may find another post about that little opening on the expansion tank possibly being clogged. Try it then bleed the system. Make sure you turn on the system with hot air and drive around for like half an hour while you are doing it, otherwise you're going to keep getting that annoying message.

[BeLiQ]

I just went through a similar problem. In my case it was the top radiator bleed screw. It is just about an inch away from the radiator cap on the coolant overflow tank. There is a small washer in the screw that goes bad. If you take the screw out you will be amazed at how small the hole is but after driving it spits out enough coolant because of pressure in the hot system to cause your problem. Bought the $2.95 part from Bav Auto and all was good. Use caution when you screw the old/new bleed screw down - if you go too tight the head of the screw will snap off - it's all plastic, of course. (p. 20-14 in the Bentley manual has a picture of the overflow tank assembly with the screw visible to the right of the radiator cap.)

I will try and see if it is similar. But as far as I know we have different systems. M60 is self-bleeding no screws. My bad I didn't specify in the first post what car is it. Help appreciated!

I had similar symptoms...low coolant warning with the AC on. Chances are it has nothing to do with the AC being on. I pressure tested and couldn't find where the leak was coming from. Finally I blew compressed air into the hole by the fill on the expansion tank and PROPERLY bled the system. Haven't had a problem since. If you do a search you may find another post about that little opening on the expansion tank possibly being clogged. Try it then bleed the system. Make sure you turn on the system with hot air and drive around for like half an hour while you are doing it, otherwise you're going to keep getting that annoying message.

Will try that and see what happens. I had the feeling its leaking from the overflow pipe on the expansion tank.

[theos]

Yeah, it's more than likely pure coincidence that you're losing coolant while the AC is on. Do a proper bleed and make sure you have a good coolant level, then go from there.

If it happens again and you see coolant on the ground start checking all hoses, aux water pump and heater core.

[BeLiQ]

Aux water pump is brand new did it in February or March. So if bleeding doesn't help maybe heater core and hoses.