[Chrisguilday]

Hello guys, I have a 2011 335I that I just replaced the T-stat and water pump.

The problem is the pump is now turning on whenever I unlock or lock the door even if the ignition is off.

For some background: My water pump was malfunctioning, had it diagnosed by a tech and he said it was bad. I installed a new one, and the first issue came up after I bled the coolant system, the pump turned on & off like normal over the 12 minutes however toward the end it just stayed on continuously (I let it run for about 18 minutes) and that killed my batter. I jumped the car, the car acted like it was in limp mode (I assume due to a dead battery) and the car overheated within 3-4 minutes. Right when it overheated (255F) the T-stat finally opened as I was pulling into my driveway and the temp plummeted to 185F. I assumed it wasn’t functioning correctly due to the dead battery.

So I put my charger on it, but when hooking up the charger it caused the water pump to continuously run. I googled the issue and people said a dead battery could be causing this and to charge the battery without it hooked up, so that’s what I did. However now it’s fully charged and my water pump turns on for about 45 seconds after unlocking or locking the door (no, it’s not the fuel pump)


Any idea what the issue could be?

[Chrisguilday]

Update: I drove the car after fully charging the battery and it’s still overheating. I scanned the car and I got water pump code 378F: Electric coolant pump missing.

Obviously the pump does turn on because just a few minutes ago it turned on when locking / unlocking the car. However I just drove it and when it overheated I tried locking / unlocking the car and it didn’t force the pump on anymore. Is there a relay that could be bad that could cause this issue / code?

After pulling over I turned the ignition on / off and the pump finally kicked on and the temp plummeted. The pump is clearly not cycling on / off correctly.

[whyzee125]

Which brand of WP and Tstat did you use? Is the battery original? Any other electrical issues that could point to a failing alternator?

[Chrisguilday]

Originally Posted by whyzee125

Which brand of WP and Tstat did you use? Is the battery original? Any other electrical issues that could point to a failing alternator?

Both the battery and alternator are like 500 miles old, not the original of either. I doubt it’s either of those things. I just updated my prior reply, and after the car overheated I turned the ignition off / on and that finally cycled the pump on and the temp dropped to 190F from 250F. So the water pump is not cycling correctly. My first thought is a bad relay or something? I am not that great with electrical stuff though so I don’t know.

And no, no other electrical issues or battery / alternator issues.

[Chrisguilday]

Originally Posted by whyzee125

Which brand of WP and Tstat did you use? Is the battery original? Any other electrical issues that could point to a failing alternator?

The pump and t stat were bought from fcpeuro. The T-stat is borgwarner and pump is pierburg https://www.fcpeuro.com/products/bmw...ly-11537601158

[Chrisguilday]

I am wondering if maybe the electrical connection to the pump or T-stat may have gotten some water in it previously or might not have a perfect connection. When I changed the pump and T-stat the connectors seemed to either have oil on them or some kind of liquid. My pump did a similar thing as to how it’s acting now before I replaced it, almost the same problem but now it’s worst. I sprayed the connectors with electrical contact cleaner before connecting it to the new parts but I am going to double check it.

[Hoody007]

Originally Posted by Chrisguilday

I am wondering if maybe the electrical connection to the pump or T-stat may have gotten some water in it previously or might not have a perfect connection. When I changed the pump and T-stat the connectors seemed to either have oil on them or some kind of liquid. My pump did a similar thing as to how it’s acting now before I replaced it, almost the same problem but now it’s worst. I sprayed the connectors with electrical contact cleaner before connecting it to the new parts but I am going to double check it.

This sounds like a BSD issue. I’d check the wiring to the water pump.

[Chrisguilday]

Originally Posted by Hoody007

This sounds like a BSD issue. I’d check the wiring to the water pump.

Yeah I agree, that’s what I’m doing now.

[Chrisguilday]

Originally Posted by Hoody007

This sounds like a BSD issue. I’d check the wiring to the water pump.

Good news, I fixed it. It was the electrical connector to the water pump. It wasn’t pushed in all the way because the clamp for the water line was oriented in a way where there was almost no clearance. There was also a verrrrry small amount of oil on part of the connector which I doubt had any influence. Anyway I disconnected the battery, pushed it all the way in and now it seems the pump is working correctly, no weird issues. My temp doesn’t go any higher than 230. It seems to really like staying right at 225-230, is that normal? (Water temp, not oil) I think it is.