So the other day my mini overheated and blew coolant out of the expansion tank cap (the expansion tank is aluminum so I know it was the cap). This happened while idling after I turned the AC off. I figured it was the fan at fault as the thermostat seemed to be working OK, and I wasn't leaking coolant other than what blew out of the expansion tank.

I replaced the fan today, but now the coolant temperature isn't getting hot enough to trip stage 1 or 2, so I turned the AC on to get stage 1 running, but the new fan does this intermittent turn on then off deal? I can't seem to find anyone else that has run into this issue. Is the new fan bad? The old one would stay running while the AC is on, and I took it for a few drives after installing the new fan and haven't had any overheating issues so I'm kind of at a loss here.

Should mention too that the AC hasn't been working that well, it may just need a recharge but wasn't sure if it could be related at all.

 

The expansion tank cap is designed to relieve pressure if the system pressure exceeds 16 PSI, so it bleeding pressure off isn't uncommon, but if the car overheated and blew the cap off you have other issues.

Have you checked the system for leaks, proper coolant level, the radiator isn't covered in grime and road debris?

If the fans stopped working after you replaced the fan then I would start your diagnostic there. Did the new fan shroud come with the wiring and a new hi/low speed fan resistor? If not you will want to start there.

Being a small engine they are fairly thermally efficient, so getting to temp shouldn't be an issue.

With the AC on the fans should cycle every minute, that is proper operation.

Try unplugging the temp sensor by the thermostat and see if the fan goes to high speed, (with the car off).

If you have cooling fan problems then yes, the AC will be lacking performance.

 

Thanks nkfry, I should clarify the cap didn't blow off entirely, just blew out most of what was in the expansion tank. No leaks in the system, coolant level was where it should be (and is again since the fix), I bled the coolant line for air as well, and the radiator wasn't grimed up that I could see when I replaced the fan. The new fan assembly came with the resistor and wiring, full assembly.

When you say the fans should cycle every 1 minute, is that basically what I was describing how the fan turns on then turns off at intervals? If that's the case it seems to be normal whereas my old fan turned on and stayed on when the AC was on, there was no cycling at all. I'll try testing the high speed to see if that works, thanks for the help!