1st Gen R53 Cooper S Heat not working, MINI overheating!

So this morning was a real cold one. About 0ºF here. I started my MINI and let it warm up. I have a ScanGaugeII so I have it display the water temp at all times just to monitor it and MINIs don't have that feature, just a dummy light. So the water temp gets up to about 165ºF when I get back in my MINI to drive to work. So I turn on the heat and drive down the road and noticed the heat was blowing cold air still and the water temp had reached 200ºF! So I turned around and made it home, and it was almost up to 215ºF. So I popped the hood, carefully removed the coolant tank cap, and checked the coolant level and it was perfectly fine. After letting it sit about 10 minutes, I started my MINI again and it started to overheat again and the heater still wasn't working. So I let it sit for about 10 mins again and tried it again. Started my MINI and the temp was about 195ºF when I turned the heater on it finally started working! And then I noticed the temp gauge dropping quickly down to about 180ºF which it normally runs at during cold spells like this.

So I'm trying to figure out exactly what could be going on here. I know one time earlier this winter when it was about this cold, the heater did the same thing but it started working a couple minutes later, but my MINI didn't overheat at all or even get above 200ºF like it did today. So what do you guys think could be going on here? The coolant isn't very old, probably about a little over a year old. I never had this happen before. Bad water pump? Bad heater? What do you guys think might be the problem?

I have a 2005 Cooper S (R53) with about 150K miles.

 

I replaced the thermostat about 3 years ago. I looked at the housing on it this morning and it's not leaking like it did last time when it was bad. I will obviously keep that in mind though.

 

Thanks for the info guys!

Yeah the fan never even kicked on from what I could tell. It was brutally cold out this morning, hovering about 7ºF while I was driving. I'm thinking there might be something going on due to it being so cold. Last time the heat wasn't working, it was about this cold out. Unfortunately, it's going to be this cold all week and weekend and I don't have a garage to work in so it's not going to be fun....

 

From what I have noticed, my running temp is usually 193ºF during the spring/summer/fall, and during the winter it will run anywhere from 180ºF - 193ºF depending on the outside temperature. Normally, the colder it is, the lower it runs at, but that would be expected due to the lower air temperature. It's just weird to me. Does the thermostat control the water flow to and from the heater core? If it doesn't, then I could probably rule that out. I am leaning towards it being caused be the water pump as it would seem more logical. I have high mileage (~150k) and I don't know if it had ever been replaced by the previous owner.

 

Yeah my friend's MINI threw an EML light yesterday and was in limp mode on her way to work. She let it warm up for 30 minutes on her way back from work and didn't have any issues. I'm just guessing it's my MINI's way of saying "Hey! Don't drive me in the winter! Get a winter beater like the rest of New Englanders!"

 

That sounds logical! I'm pretty sure the mixture is good, but I'm guessing I could flush the system out and replace it with a more concentrated mix instead. It was a 50/50 mix when I replaced it last time, but I am human and can make mistakes! I will try that out and see as my MINI did start working fine after sitting for a while after being hot. Could have easily had a blockage somewhere due to ice forming, and then it finally melted and the heater started working and the whole system dropped down to normal winter running temps.

Thanks everyone for all the info! If you have anything else you think it could be, by all means let me know!

 

I'm leaning toward a bad mixture like MCS02 stated. I think that would be a good place to start as this could easily cause the problem, and also check for air in the system. Then from there I will figure out if it could be the pump or the heater, and then possibly the thermostat. Hopefully a new batch of coolant and no air in the lines fixes it! I will definitely let your guys know!

 

Just went out and check my MINI. It's a comfortable 20ºF out right now, check the motor to make sure it was completely cold, which it was, and the ScanGaugeII confirmed this as it read the intake air temp and water temp as also being at 20ºF. Fired her up and let her run for a few minute, got up to about 100ºF according to the ScanGaugeII and turned the heat on and it was working fine, well what it should be at that temperature. So I'm guessing it's just a bad coolant mixture being as it's only 13º warmer out and it didn't cause the coolant to freeze anywhere or cause any problems. So I guess I'll be changing out the coolant. How much coolant does the system take if it's empty? Jeffster06 told me to use a turkey baster to remove coolant from the reservoir and then add in unmixed coolant to offset what is currently in the system. I can't recall how much these cars take.

 

I like your way of thinking Jeff! More time in the warmth for beer!