So my girlfriends 2004 Cooper S started overheating about a week ago.
The first thing I did was drain the coolant, refill and bleed the system. Nope, still overheating.
Today, I replaced the thermostat and thermostat housing and re-bled the system again. Still overheating.
I'm going to order a new coolant cap because it's a super cheap and easy potential fix and something else to rule out.

I'm not super familiar with Mini (I drive an E46 BMW though) and gosh those hose clamps sure are fun to remove!

I'm pretty confident it's not an air bubble trapped in the system or a stuck thermostat since I have addressed those things already. I'm thinking the next most likely thing would be water pump and my research reveals this is not a fun job at all. Is there a simple way to test and diagnose if the water pump is bad?

I'm just trying to get a gameplan together for next weekend and figured I'd ask you guys for your advice. The car overheats and there's no cabin heat, even though I just replaced the thermostat and drained and refilled and bled the coolant.

I have read the forums and seen the information about the low speed relay and resistor. When the car was idling on jack stands I scooted under there and could physically see it spinning. I think I could tell when it turned on high too because it was extremely loud. I am familiar with the coolant temp on the dash too, I can't remember the exact temps where the fan switched on though.

I'm thinking water pump, but want to ask for opinions. Thanks so much for any help and advice!

 

 

 

I would not worry about replacing stuff that's not the cause of the problem until you find out "WHY" you don't have coolant movement inside the expansion tank.

Water pump or water pump drive would be the first things I would be looking at

Bryan

 

 

Are you sure you put the thermostat in the right direction? You might remove the thermostat and put it in water on the stove and make sure it opens at the correct temperature. Would also tell you if it’s good or bad.

 

 

He should still get heat from the heater, which he doesn't....which tells me that water is not circulating ......which leads me to first checking the water pump drive or the pump itself

Bryan

 

Back again with an update. Water pump is definitely bad (broken impeller shaft), but even worse... the shaft on the supercharger broke off one of its teeth. The supercharger impeller has two tabs at 12 and 6 o'clock and they mate up with the inlet on the waterpump which then fit in at 3 and 9 o'clock. So both the drive impellars on both the water pump and supercharger are broken. I guess protocol is to take the supercharger off and send it out to get rebuilt? I googled around and found a service that does this, it's like $1500ish. Any advice?

 

In the pic below, you can see the tab on the lefthand side is broken off.

 

you could probably find a good used supercharger for around $500 - $700.....make sure it turns free....do an oil service on it and then put a new water pump on.

I'm sure someone will chime in if I'm way off base....

There are even a number of people parting out SC cars in the first gen classifieds here

Bryan

 

X2 what Bryan says. No water movement is an indication that the pump, or gears have gone to hell!

 

Good to know the root cause. The end plate can be sourced from shops that specialize in superchargers though you may want find a used or rebuilt supercharger as a first option instead.

Call around to a few local wrecking yards to see what’s available. If nothing, I’d start thinking about a new one at about $1200 from Mini (of Kennesaw)

i bought a used one a few few months back from a wrecking yard for $250. It was a gamble, but turned out to be really clean and in great shape. With a new pump and an oil change for the S/C, the car is running well again.

 

Edit: whoops see next reply underneath this one

 

Fixed the overheating issue! I just reinstalled everything even though the supercharger tab is broken off. Well that side is half broken since it’s only the part of the tab that protrudes which broke. So of 4 total tabs, it’s in 75% health lol. The 2 tabs on the water pump are good and only that 1 protruding tab on the supercharger is broken off.

Took the car for a spin and it’s not overheating anymore. The coolant temp in the secret menu is holding steady at low 90s Celsius.

I’m gonna pull everything back apart when I figure out what I’m gonna do with the supercharger. It’s a big purchase and I want to sleep on it for a couple days. Nobody is gonna be driving the car any time soon anyways since it needs tons of suspension work too. It’s a 115k mike car and it basically needs a full rebuild.

all in all it was a pretty difficult job, but now I know how to do it for next time!

The thing that sucks is how filthy it is down there. There’s years of oil leaks and the CV boot on both sides tore which made a HUGE mess. I’m almost thinking of pulling the motor and disassembling everything so I can properly clean it and get all the gunk out. It’s tough to see oil leaks right now because of how thick the grime is.