Yesterday I decided to figure out how much the forks could compress before the front wheel impacted my oil cooler. I removed the front fender, placed my XR650L on a stand, and measured the free sag at 1-1/8 inches. Taking the bike off the stand, I measured the travel from the wheel to the bottom of the oil cooler at 9-1/2 inches.
Adding the free sag to the last measurement, I got a total wheel travel of 10-5/8 inches. Therefore, the wheel will impact my oil cooler in the last inch of travel. I'm convinced 10-5/8 inches of fork travel is sufficient for the way I ride my XR650L, so I have decided my oil cooler is positioned high enough.
Incidentally, I raised my forks one inch when I installed my lowering link. Therefore, a stock bike would be able to accommodate maximum fork compression without striking my oil cooler.
Since the weather was nice, I rode my XR650L for 56 miles on the freeway, without the fender, to discover the highest level of cooling I could expect.
I maintained 75-80 mph the entire time, and passed a lot of automobiles along the way. My oil temperatures did not exceed 255 degrees; I am pleased with this result. Of course, once I exited the freeway, my oil temperatures quickly dropped to much lower levels.
I am going to trim my front fender a bit more, to ensure the wheel will not impact the fender before it would impact the oil cooler.
I will also drill a few more holes in the fender, and test to discover if the drilled fender allows cooling similar to a fenderless setup. If the cooling is significantly less with my drilled fender, I will cut a large hole in the fender and install some aluminum hardware cloth.