Might also check your viscous fan clutch. If your engine is hot and you turn off the ignition, the fan should stop immediately. If not, the viscous fan clutch might be going. (A two man test.)

Just replaced mine - 1981 300SD w 279000 miles - and was very easy job. Symptoms were that it ran just a touch hotter than normal per the gauge. So far has resolved the problem. Since I am the original owner, I know exactly where the needle should be on the temp gauge.