Although these diesels do have temp climbs under load, 110+ is pushing the envelope in my book.

I am sure you do not want to get to involved far from home. If the fan clutch and aux fans are running normally you might consider 1) a bad rad. cap 2) blocked radiator 3) bad t-stat

Which of these can be tackeled out of the confort of your own garage? The cap might be the easiest to rule out - so try that first. If 2 and 3 are impossible for you to do, either bite the bullet and take it to a mechanic or top off with some synthetic, add some Water Wetter (Pep Boys in PA) and hope for the best. It might be a hot ride home.

If you are near Phily, I live in the suburbs and have a garage to which you are welcome. I also know some great Benz mechanics if a more thourough diagnosis is needed. Best of luck!!