Bought a 2003 Mini Cooper S a few weeks back with 115k on it. The car was overheating. The owner claimed the cooling line T broke and it overheated. They replaced the T, the expansion tank and the thermostat. The also claimed to have replaced the water pump since it was dripping. All claims, no paperwork or anything to back it up. Anyway, towed the car home figuring... how bad can it be? This is my first Mini so I am a learning the hard way.

Anyway, car would overheat within about a mile of running. The coolant would pour out of the expansion tank the minute it got warm. No coolant in the oil or oil in the coolant. I figured it overheated hard and the cylinders might be pressurizing the coolant system. I pulled the head and put in a new head gasket. The head went to the machine shop and it came back good. They decked it about .010" to clean it up. While I was working on the car I noticed the low speed fan circuit wasn't working so I installed a new fan. Got it all back together and spent a bunch of time bleeding it.

Same thing. Within a mile it would overheat again. One thing I noticed this time is that when I was warming the car up I could not get heat out of the heater or defroster. I am now assuming that I am not getting any flow in the coolant system. I did bleed it a half dozen times with no luck. Right now I am thinking I either have a bad water pump or the PTO on my supercharger is bad. Any easy was to test the flow of coolant? Can I just pull the top radiator hose and see if it pumps the coolant out? Appreciate any advise before I pull the supercharger off next.

Chuck

 

Did you put in a new thermostat when you pulled the head? If not, I’d start there.

These are a bugger ti bleed. I hook up my scanner and monitor the temp. When it reaches around 200, I shut it down and let the coolant move naturally. Remove the coolant tank cap and open the bleeder in the front. Leave for a few minutes, close and repeat.

After about 3rd time you start seeing fluid getting pumped into radiator. Open front bleeder and use a flashlight to watch flow. Close when coolant starts streaming out of bleeder.

It’ll take a few short drives from there to get all the air out.

 

Bleed process is very specific. There are two bleed screws…

details in Bentley and TIS

id make sure cooling system is bled. You should see a stream going back into the reservoir near the cap

 

A stream would imply the water pump is working. No stream, no heat in the heater core.

 

I use my MOTIVE brake bleeder on the coolant reservoir. The thread on the cap of the MOTIVE is the same as that of the reservoir. Pressurize and then crack the bleeder screws one at a time to allow any trapped air to escape. Close when you see nothing but coolant.

 

Thought I had it. Pulled the thermostat (supposedly new). I put it in boiling water. Even by 215deg it wouldn't open. Ran out and got another thermostat and a gallon of coolant. Spent a lot of time bleeding (both screws). I let the car idle and warm up. When the thermostat opened, I bleed it some more till I got no air bubbles. Let it idle some more and now the fan kicks into high speed. At that point its boiling out the reservoir and the bleed screw by the radiator is nothing but steam. Let it cool down and tried two more times. Last time, things were looking good. Drove it literally 100 yards and it was puking coolant again.

I'm seriously running out of options. The only one left is to check the water pump and the supercharger PTO. I picked up a spare supercharger locally cheap just in case things go south. At this point, this is not how I want to be cycling my new head gasket.

Chuck

 

Does anyone have a diagram of all the coolant lines? I want to make sure the previous owner didn't cross something up.

Thanks,
Chuck

 

I don’t have a diagram but I did take some pics

ill have to dig them up tho

 

I think I mapped it out via part diagrams. There is some flow paths in the system example heater core even if the thermostat is closed. The small hose from the water pump goes to the heater core and back to the block at the thermostat housing. So even if the thermostat doesn't open, the heater core will act as a mini radiator. Problem is, my heater core never gets warm which indicates a heater valve issue or no flow from the water pump. Also the coolant recovery tank is in parallel to this same loop. If the pump was "pumping" I would see coolant circulating in the coolant tank.

When my thermostat opens, the top hose gets warm but I don't think I am seeing any real flow. Within a minute I can hear steam being created in the block. From a background, the head was pressure tested, new gasket, new fan, new thermostat etc. Everything seems to be point to new coolant flow. Maybe a plugged radiator although that wouldn't prevent the heater from getting hot. I scored a nice used supercharger with water bump off my local Craigslist for $75. I just yanked it apart and its in real nice shape. I'm going to replace the internal seal from the rotor to the PTO gear, reseal the cases and fill it with fresh oil.

I'm going to tear the water pump out tonight. If I need a new water pump (broken impeller or shaft??) no biggie, if the PTO drive is bad, I'll be ready to go with another supercharger. Luckily the novelty of the car is still fresh. if this was my daily I would be a lot more annoyed ripping it apart for the third time.

Chuck

 

So reluctantly I pulled everything off the front of the car to get access to the supercharger. I say reluctantly because I was afraid I would find out the water pump wasn't the problem. At which point I would have to admit I have no idea how to bleed a cooling system. While I was under the car pulling the little belly pan thing I stuck a screwdriver in the PS fan. Sure enough the blades were stuck. No... that wasn't THE problem. Just one more broken part on this modern day reincarnation of the MG. Seriously, every part I touch is broken. Anyway, another part to hunt down.

Got the lower radiator hose off the supercharger. If you look up the inlet into the water pump you can see the impeller. I had my wife crank the car while I shined a flashlight into the pump. Sure enough, the impeller isn't turning. Also I can now here a buzzing sound that I couldn't hear when everything was connected and full of water. It's either the shaft spinning in the impeller or the sound of stripped teeth in the supercharger gearbox. Decided to call it a night. I'll finish pulling the supercharger this weekend. I'll either replace the water pump or be swapping the supercharger for the soon to be rebuilt one on my bench. And of course looking for a PS fan...ugh.

Chuck

 

Good work sir

i know what you mean about everything breaking. I’ve owned the car for some years now so I think its just my new normal. Are all cars like this? I can’t remember

 

I think the hardest thing in the cooling systems is learning how it works and the directions. Took me forever to figure out VW cooking.

 

SC is off. The last owner did put on a new water pump like he said. Unfortunately there was nothing left to turn it.....


Not horrible....

Wait, where is the middle of the teeth?

Spare I got for $75

Just waiting for a new seal for the rotor shaft that drives the PTO gear. Figure after 18+ years I should install a new one. Might as well install 15% pully while things are in pieces....

Does anyone know what type of grease to use on the needle bearings on the back side of the rotors in the supercharger?

Chuck