The coolant tank has min and max level marks on the outer surface but because the tank is opaque it is very difficult to tell where the level actually is. Looking down through the cap there is a 'curly que' of plastic inside which should make it easier to judge the depth of coolant, but the owner's manual is silent on this issue! The top of this curly que appears to me to be roughly the mid-point between min and max, but its hard to tell. Thoughts anyone? TIA.

 

Chop stick?

 

In actuality, most folks think as you have described and, as the level drops, they re-fill, only to see it drop again because it's been overfilled. I've found that the correct level is just below those "curly-ques". If it continues to fall, then you need to pressure-test the system and find the source of the leak.

 

For about ten years I have kept the coolant level in the oem tank to just at or above the baffles or curly things and have had no problems. That puts the fluid above the min mark well below the seam. At or above the seam often causes a leak. Since the tank had darkened with age, I had to remove the cap for a visual level check. There is about 18 ounces of coolant in the tank when at or just above the baffles. Recently I replaced the ten year old oem tank with a metal one that uses the oem cap as a precaution. It was priced about 25% more than an oem tank and well worth it, especially for the peace of mind. As a note, the installation of the metal tank is very easy. There are a number of instructions online. Do make sure, if it is a DIY, that the the installer of the attaching bolts has smaller than average hands and wrists. It's a tight fit.

 

I use a flashlight to help with this if I can't see it from the outside of the tank. I'll put it to the opening and point it down so that it shines into the tank. It lights it up enough to see the fluid from the exterior with the lines, depending on how bad your tank is. Maybe try this out and see if it works for you.

 

Pelican: Yes, I have tried that, but my tank is simply so opaque that it is difficult to determine the actual level of the coolant in the reservoir. I have decided to use the top of the plastic scroll in the tank as the target level; what I don't understand is why MINI doesn't suggest that in the owner's manual. They put that scroll in there for a reason.

 

I think the scroll is a baffle of some kind.

 

As do I.

FWIW, I measured the depth from the top of the fill cap to the top of the scroll, which puts the top of the scroll right at the mid point of the Min/Max scale on the side of the tank.

As long as your coolant level is just above, at, or just below the level of the scroll, you're OK.

 

The measures depth method is most likely the best way. Have you tried an brighter LED light. flashlights are sometimes to dim on the older yellow tank. I tired the LED flashlight and it helped. I used it on an older yellowed R56 tank also. But its easier to see n that tank.

LED flashlight

 

DO NOT OVERFILL....the level should be at about the seam..slightly lower....overfill...and the tanks split or the seams leaks....I found keeping the level right kept the tanks to about a 60,000 mile life....too full...and BAM....
When cold, I would just take off the cap, and look....use you finger if you must...a flashlight shining from the side, held against it works too, but depends on how YELLOWED the container is...they change as they age, and MINI DID go to less translucent plastic to try to to fix failure issues....the height of the baffles, AKA scrolls, is about right....