My '03 R53 started overheating on the way into work a couple weeks ago, so I had it towed home and started tearing into it. I had almost no coolant in the reservoir, and when I drained the system, I didn't get a whole lot out. So then the question was - where did the coolant go?

Looking at the forums, I figured thermostat and water pump would be likely places to check, as there was no apparent leakage from the reservoir tank itself. After spending way too much time encountering certain hard-to-access bolts and needing to make a couple runs to hardware stores for things I should have already had in the toolbox, I finally dismantled enough of the front end to see where the coolant was coming out.


The blue arrow shows the source of the leak, and it's apparently been oozing for some time. The green arrow is the water pump flange.


Turns out this part is available at Pelican or ECS Tuning. Part number for this and the seal are 11111487594 and 11111487596.

 

The threads I did find regarding water pump replacement have been immensely helpful in getting this far, and the how-to's on this site and the step by step guides on Pelican Parts are fantastic.
Since I'm already this far, and the car has 130,000 miles on it, I figure I'll replace the thermostat, water pump, and radiator hoses now just as preventative measures against future coolant leaks. Anything else that I should look into? Or avoid?

 

YES! I assume you'll be installing a new water pump, if not you'll wish you had, unless you're selling the car next week. Also get 2 4oz bottles of the GM supercharger oil and "change" the oil in your supercharger. At minimum top it off but the oil should be changed. I pulled my SC to make it easier and had the appropriate gaskets on hand. Also while it's in front of you replace the crank sensor o-ring. If it's not leaking oil today it will tomorrow

Finally I would replace your idler pulley and tensioner assembly if you haven't already. Throw a new Continental belt on it and you be good to go for another 100K

 

Already on the list. I noticed that the supercharger is pretty oily inside; looking for more answers on that one too - if there's a seal I can replace or if there's another problem that will require replacing the whole thing.

Don't I have to jack up the motor to get at the tensioner? I put on a 15% reduction pulley on the s/c in 2012, which came with a new belt as well. I'd like to replace it at some point, and while I'm at it check on whether new motor mounts would be beneficial.

 

Idler and tensioner can be changed without lifting the car. When you're in the wheel we'll take a look at the harmonic balancer. Inspect it for cracks. Mine was shot at 90k.

Regarding the SC, if you want to go all out go to the Eaton website to look for authorized rebuilders. There's only 3 in the US. You can find rebuild kits for $400 or so but it's all aftermarket. Eaton shops will do the whole thing for $750. You probably can get by with a good SC oil change.

I bought my water pump from Pelican. Two months ago they had 3 brands. I recently checked and they only had two, MINI and an 80.00 off brand. Go with the mini for the $60 extra dollars

 

Thanks again for the advice on my project.

I wound up changing the oil in the sc - which pretty much meant putting oil in it... wasn't much left in there. I put on the new flange on the engine block, and also replaced the water pump, radiator hoses, thermostat, miscellaneous gaskets/bolts/hose clamps, crankcase vent valve, fuel tank breather tube (to fix a vacuum leak code - p1447 or something like that...), coolant tank, and belt tensioner.

Unfortunately, the car is still experiencing a slow coolant leak when I drive. I haven't been able to see a place that looks like it's damp, but then again, it's a pretty cramped engine compartment. Maybe a tiny crack or hole in a hose? Any suggestions on where to start looking for a leak?

 

Did you look at the oil cooler...passenger side wheel well area...
And finely the radiator...after about 10 years of getting heat cycled, they tend to crack where the aluminum fins are "welded" to the plastic side tank....or where the hose connector is attached to the tank...
You can get aftermarket copies (exact fit) for about $100 on rockauto.com or other vendors.

 

I just went out and took a look at the oil cooler... it's too hard to tell because it's - you guessed it - oily. I'll give it another go when I have a bit more time and patience to clean it off.
For the radiator, what's the best way to see that? Remove the splash guards from underneath?

 

any updates?

 

I'm have the same issue, small coolant leak. The expansion reservoir is leaking pressure and it looks like there is a crack in the seam so that is first on the list. Could that be leaking coolant?

 

The expansion tank was the source of one of my leaks. I haven't figured out where it's coming from now when the car is running; I haven't seen any kind of puddles or drips on the garage floor, so I think it has to be coming out under pressure and maybe burning off on contact with the engine or exhaust manifold?
I've been putting off getting it up on jackstands and disassembling any of it because of other projects (and humidity + mosquitoes). I'll try to get to it and let you know what I find out this weekend.

 

Have not seen that may with the block off plate leak. Looks like it barely dripped and then built up. Then started to drip down later on.

Cover Plate Part # 11111487594 which comes with that seal ( 11111487596 ) .

http://www.ecstuning.com/Search/SiteSearch/11111487594/



#7 , seal is #8


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The connection flange which sets on the engine toward the water pump I have seen leak on some MINIs.


Connection Flange Part #11517509170

http://www.ecstuning.com/Search/SiteSearch/11517509170/




I would do both since you are there. Which I believe you did.

#3 in the below diagram.




+1 on the checking oil cooler ( heat exchange ) near the oil filter housing , you can see it somewhat from the passenger side wheel well. For Cooper S w/ manual transmissions.

https://www.northamericanmotoring.co...this-part.html




Thanks

 

Yep. It was pretty nasty on there.
I did order those parts from y'all at ECS. Fast shipping on that I've heard of problems with the water pump o-ring sometimes going in a bit janky and leaking; I hope that's not the problem - not really excited about the possibility of having to take apart everything I just put back.
I also just replaced the timing chain tensioner and cap (again, ordered from ECS), and poked around at the oil cooler a bit while I was in that region. I didn't see anything that looked wet around it though... I'll take another look from underneath when I get the car up on jack stands.

 

Thanks, we appreciate the kind words and thanks for the orders. I hope you can track it down and return to more motoring.

 

I've an 02R50 - been slowly leaking for years. Never tore it down to find. When replacing clutch I made a point to find the leak. It was the temperature sensor. There's a band of thread sealant on the brass threads that simply leaked! I replaced the sensor and all other coolant parts and Teflon taped the threads on the temp sensor. There was NO trail or corrosion. It leaked in drops onto the tranny and down into the steering cooling fan.

 

I've had 2 thermostat gasket leaks and one temp sensor leak on my 2003 R50.

 

The temp sensor was just talked about here: as well as the Thermostat housing on the Cooper S models ; Gen1 .

https://www.northamericanmotoring.co...mp-sensor.html



Two other locations to check.

 

Another problem recently popped up with my car - it seem sluggish getting up to freeway speed, and once I get to about 65mph, the car refuses to accelerate. It actually slows to about 60 mph, and doesn't matter if I downshift from 6th to 5th either. The RPMs stay pretty constant at that speed, regardless of whether I'm applying just a little pressure to the pedal or mashing it to the floor. And I got a whopping 15 mpg on my last tank of gas - that's mostly driving on the freeway. I'll be searching other threads for troubleshooting that, too.

The project has been sidelined for a bit, as I'm helping my folks move and since I got my hands on an '06 GP... But I do need to get the car running to be able to sell it or use as a winter car.