1st Gen R53 Cooper S Small leak under car, next to oil pan - what is it?

Sometimes when the old filter element gets pulled during a filter change, there is a quantity of old oil that can run out and down the engine. Could this be some of what you might be seeing?

 

Being an '06, it's probably just about time for the crank sensor O-ring to have deteriorated to the point that oil will start blowing by. Gunks up the front of the block and pan, but seemingly never enough to drip or leave spots on the floor.

Very common 1st Gen issue. That's what I'd look at first.

 

And the crank sensor is on the other end of the engine. That is the transmission side. All cars leak or rather seep a bit of oil. I'd recommend checking the trans fluid level. If it is OK I'd take a wait & see approach to it.

 

I would guess that a couple more possibilities are the oil pan gasket or the rear main seal. You might want to look further up and around the engine with a good light to see where the oil is coming down from.

 

Correct, you can wait until there is a need to pull the front end. I've stopped my leak to have it return a few years later; now that I know where it's coming from it doesn't bother me. Your's however is more than just weeping.

The crank position sensor is located on the front of the engine below the water pump location. From the photo the oil doesn't appear to be dripping from the weep hole and bolt nearby, which would indicate a bad rear crank seal or transmission input seal. The fluid can be dabbed with a wipe and smelled to determine if it is gear box fluid or engine oil. There is a remote chance it could be from the supercharger's water pump drive. Remove the lower air dam/splash panel and have a look upward with a lamp or flashlight and mirror.

 

Guessing that you have already inspected to see if the fluid is running down from some place else... With that I'd wipe it clean and run the engine while watching the area, if you don't see anything coming out then drive it for a bit and see if it has returned. If not drive it a day and inspect again.... You could also torque those bolts to spec in that area by backing them off and then torque back down... Then keep and eye on it to see if it returns... 2 cents

 

Am I mistaken or does that 'oil' look blue? I had a couple of blue drips on the garage floor and wound up having the thermostat houseing service. The service guy called it Smurf Juice. The brown oil is so spread around it could be from anywhere. minimark's idea makes a lot of sense but I'd still investigate that blue stuff.

 

Maybe you have a weep from the crank sensor that is being washed down by a leak in the water pump seal. That could explain a bluish oily tint. Check your coolant level, and try putting newspaper under the car overnight.

 

Might inspect the drive shaft seal on that side, recently had to have one replaced and it was leaking down....

 

Its most deffinitely the crankshaft sensor o-ring. I am a Mini Technician and would most-definitely sell that to you in the shop. I would recommend removing the belly pan and inspecting further. It you see oil coming from above the pan then it is one of two things. The throttle tube gasket (green-between black throttle tube and supercharger-leak over time) or the crankshaft sensor o-ring. It's most commonly the o-ring. To fix the oil pan gasket is just over 4 hours and the same with the other repairs. Parts range from about 3.00 to 50.00 depending on the part replaced. Keep in mind that does not include oil if the oil pan gasket is replaced if deemed the cause(doesnt appear so in picture).

 

Its the O ring im sure, if thats not it its the rear main seal.
Pull the front end foward and check it out.
The crank trigger is exactly where Khuevo said it is.

 

FYI: I replaced the crank sensor o-ring while doing some other work on my '06 MCS, but I did a crank sensor o-ring replacement this last weekend for a friend and I did a write-up on how-to do the work yourself: http://www.motoringalliance.com/library/1st-generation-mini-cooper-how-to-3/crank-sensor-seal-replacement-103/

 

With the ratchet strap trick, it's easy enough to do without removing all of the stuff. It probably took less than an additional 30 minutes to do when doing an oil change.