Hellooo,

I've owned my R53 Mini Cooper S for about two years now so my mechanic has changed a fair bit of parts on the car, however one problem doesn't seem to make a whole lot of sense.

When I'm driving at higher RPM my car suddenly starts overheating, most of the time issues occur when the RPM hits 3000 or higher. It has overheated one or two times when I'm driving in town, but the vast majority of the time it's on highways or faster roads. I checked the coolant level a day after the first time it overheated and it hadn't dropped at all and hasn't dropped since, so I don't think a leak is causing the problem. The coolant looks clean and as it should (no debris or anything)

About 3 weeks ago I brought the car to my mechanic for him to look at and told him the story as shown above. He had already changed the thermostat (thermostat itself, housing, etc.), expansion tank and radiator at different times. He started to driving the car for some time (highway at 150km/h or around 90mph and standard town driving) but he couldn't seem to reproduce the overheating. After driving the car he did a pressure test and everything seemed fine. Cooling fan kicked in and functions as it should. The flow of coolant in the radiator wasn't the problem either. The only thing that was replaced at this time was a hose going to the radiator because of a tiny leak with an o-ring. He send pictures through the whole process everything he said was shown on the images.

After I picked up the car I didn't experience any problems for about two weeks, but the same problem has returned.

The only cause I can think of is the water pump. On another thread someone said that the supercharger is connected to the water pump, so my theory is that when the supercharger starts to rev higher that a faulty water pump couldn't handle it. Idk if this is a valid theory but it was the only thing I could come up with

If you know any possible solutions to the problems please let me know!!!

 

When you say over heating do you mean the temp of the car gradually heats up or does the temp sky rockets? When I had a blown head gasket, 1 minute the temp would be fine and another min pass and the cars smoking and the temp gauge is maxed out. It matters how long it takes to overheat. If it was a gradual process to overheat, I would say something is not being flushed through the coolant system. Maybe a coolant flush? But if it’s a sudden increase in temp possible something in the “broken part” range.

 

Hi ttawfik,
Thanks for the reply! I failed to mention some things, so I'll clarify the situation a bit.

When the car 'overheats', the temperature gauge on the dash gradually goes up to about 90%, from the half way point in the gauge (car is warmed up at half way level) to the 90% takes about 10-15 seconds. When I turn on the interior fan/ventilation (only fan, so no A/C) the needle slowly comes down again to where it should be.

I'm going to look in to the thing about coolant flush but if I remember correctly this was done fairly recently.

 

Oh I see. It could be that the ventilation fan needs to stay on. I know regardless of what mode you put the fan on I would always feel some air hot or cold come through. Maybe a blown fuse that’s causing all this.

 

When the expansion tank was replaced, was the cap replaced as well? They are known to leak pressure when damaged. I don't think it's really the issue, but it's a cheap replacement to eliminate a potential issue.

To delve further in the details, I suggest taking a cheap OBD2 bluetooth reader and monitor the coolant temperature with it. The dash temperature gauge is notoriously imprecise.
When monitoring the coolant temperature, you should see the coolant climb up to about 92°C to 100°C (198F to 212F) then rapidly drop under 90°C (194°C) when the thermostat open. Then that cycle should repeat. That's what happens under normal operation.
If you drive slowly and that's not enough to cool the coolant, low-speed fan should start at 102°C (215F) then high-speed fan should start at 115°C (239F). Note that low-speed fan failure is common because the resistance tends to break earlier than other components. On the other hand, since you mention driving, it's not likely to be the problem, I'm just describing what "normal operation" should look like.

I don't have my manual on hand right now and cannot find a r53 cooling system diagram, but what enabling the heating does is enable the coolant to go through the heater core and dump some heat there, so yeah it's going to help if the system cannot dissipate enough heat via the radiator. You should still get the source issue fixed sooner than later, otherwise the next step is blown head gasket and/or wrapped head.

Something not working properly in the accessory belt / water pump / supercharger area is indeed the most likely candidate. A low coolant flow would be in-line with what you have observed.

 

+1
They also exhibit the non-linear behavior you described when overheating. In the middle, just under the tick mark means it's running at the normal temp. After that, the needle practically leaps up to the top when you overheat. Not so much an analog temp gauge as an overheating indicator.
+1
Some other possibilities
>Cooling system wasn't fully burped - these cars are notoriously hard to burp, need to have front end high, heater on max HI temp with one click of the fan speed (lowest). See the Pelican Parts tutorial on their website. Also note the car has two (2) burp screws - the one right up top in front and another one buried way down deep below the outlet side of the intercooler.
https://www.pelicanparts.com/techart...eplacement.htm
>Thermostat was not installed with the little hole at the top "12 O'clock" - this is the only way trapped air will get out of the block. Even if you do everything noted above, you'll never completely burp the car.
>Different coolant types were mixed without fully flushing the system leading to globs of gelatinous coolant mutant goop floating about the engine and clogging things. Should either use (a) the Euro Blue stuff or (b) the generic green stuff. You can mix the green with anything, but don't mix blue with orange or pink or purple or whatever else might be on hand.

Others may weigh in with other potential causes but the above are very common for this issue.

Finally check your dipstick and coolant expansion tank for signs of mixing, an indication of either a failed oil cooler and/or blown head gasket