All,

I apologize if this redundant, and I know it is. I received the open thermostat heater circuit code several months ago. It doesn't stay on, so I have had trouble just blindly replacing the thermostat. I raced small block chevy circle track cars, a thermostat took 5 minutes in a Walmart parking lot... So I've replaced the thermostat, put all back together, bled the system 4x, and the code still comes on. So I unplugged the tstat heater to see if the engine would warm up quicker. I use a Bluetooth adapter and TorquePro (shameless plug), best $50 I ever spent. Anyway, I noticed the temp climb up to 210-220 depending on when I looked and it stayed. So I wiggled the heater wire up from the bottom and probed it with a voltmeter. My tstat heater is always receiving voltage. Is that correct? The only thing that changed is when I turned the AC on and it was getting a full 12V instead of 10-11V. That can't be right. No wonder my circuit is always open, it's always on. What in the wiring or ECU decides when the heater needs to be on?

I apologize again for the redundancy but I am at a loss. And if I search Tstat heater always on all I find is replace thermostat. I did that, but it doesn't seem right to me that it is always being "told to heat".


Thank you all in advance
Perry

 

Well first, 210-220 is completely normal for these motors. That's their operating temp.

Did you buy a genuine thermostat assembly, or an aftermarket? These cars are VERY picky about their t-stat assemblies, and anything that isn't OEM will either leak or cause the ECU to throw a temper tantrum. At the shop I work at, we only use the OEM from the dealer t-stat and adapter harness. We had too many cars coming back with 3rd party replacements (even from quality companies like Vaico don't work)

 

Correct, the temp didn't bother me, only the time it took to get there. I had the car idling in the driveway for nearly 30 minutes. The highest the temp would get was 180 degrees. I checked for air, again, nothing wrong that I can tell. The cooling fan wasn't even running. So I thought I'd experiment. I wedged my hand down in there and unplugged the tstat heater. The engine temperature climbed to operating temperature and hovered between 210-220. It did that for 20 more minutes. So like I said I probed the plug for the heater and it was showing 12V. Why? The heater is always on, that's why the engine doesn't heat up. But why is the heater always being sent voltage?

I had tried to save money and purchased a Tstat from MiniMania (dealer usually equals big money). But it was completely different and I couldn't use it. So I ran over to Flow Mini of Winston Salem. Bought the OE Tstat and OE harness adapter. So I don't have any leaks anymore, I've bled for air 5x now. But I'm still hung up on why the heater is always on, keeping the tstat open.

Perry

 

Per BMW/MINI, there should always be ~12v present at the thermostat. I can email you the full component testing guide from Mitchell/BMW if you would like to have a read.

 

That would be awesome, yes, I would love to check it out. I'll PM my email address.

Perry

 

That would be great, thank you. I'll PM my email address.

 

I PM'd my email address.