Hey guys. Recently I've been dealing with an issue on my R53. I replaced the factory S/C pulley with the Alta 17% reduction pulley. Ever since it started getting pretty cold here, I've had a P0128 (Coolant temp below thermo regulating temp) and have replaced the thermostat (twice) as well as the temp sensor. The water pump and both hoses are new, and it has genuine mini coolant in it. I even replaced the fluid again to see if the Water Wetter I was using was the issue. It warmed up the past couple days, and the CEL has only come back on once at night when it was in the 30's. So me and some mechanic friends got the idea that since I have the much smaller S/C pulley, and that the water pump is driven off the S/C, that in theory the pump could be spinning and circulating too fast and over-cooling the system.

Am I crazy or has anyone else had this issue?? Help! I'm so tired of this problem.

 

Crazy hypnosis....
I have seen -5°f...in the last week...(wind chill Does not matter)...
And many folks live in colder areas with modded mini's...no issues.
Look elsewhere.

 

Other thing I'm thinking is wiring issue. Usually when that code pops on, I get a boost leak code with it, and I'm fairly certain the MAP sensor and coolant temp sensor wires go into the same loom/bundle. Also recently had two throttle body codes, one high voltage code and one low voltage code.

 

P.S. I have a 17%...have had it for years...in the cold north...

 

Sounds like you need to do some troubleshooting.....
I strongly suggest you do not just randomly swapping parts...that's $$$.
Sometimes getting a pro's help is cheaper than a ups trucks loads of parts to find it was a pinched wire...

 

The thought of the overcooling issue just popped into my head, didn't know if anyone had experienced the same problem. I work in the auto industry, went to college to be a mechanic, so I like to consider myself competent :p but I'm definitely going to go through the wiring this week, have a couple days off thankfully.

 

And thanks again for the info! Definitely helps. I probably needed to do thermostat anyways, it was taking it awhile to warm up until I replaced it the second time (that's what I get for using crap parts store stuff the first time).

 

Of the mini repair books...(if you get one)
The "Bentley" is the best by far....they run about $100 new...used about half that...much better than the others which are often just wrong or inaccurate.

 

I've got a Bentley bible on PDF for when I had my e30, by far the best repair resource I've ever used.