1989 Benz - what should the rpm's be at 70 mph?

That does sound high. Can you feel or manually engage all 4 gears?

I bought the car used about 6 months ago and it's always been like this. A friend was riding with me and mentioned they thought it should shift again. Should it have a forth gear? Do all 300SE models have a forth gear? If I supplied the VIN number would that help? Thanks, Rick

You definitely have an issue. Your RPM's at 70 should be around 2000 to 2500 - depending on your model and transmission for that year. Besides giving you terrible fuel mileage, those RPM's on a regular basis could be hastening the demise of your engine. That year came with a 4 spd automatic. Your MPG should be around 15 city and 17 hwy. When new, it was subject to the Gas Guzzler tax because of its low fuel economy.

I think a previous answer has confused km/hr with mph. 2000 - 2500 rpm is normal for 70 km/hr. 3500 rpm at 70 mph is also normal. You have four gears; however, these models start in second as an economy measure, which makes them feel sluggish, and fourth is a 1:1 ratio. Overdrive gears did not come in until 1991. You will get all four gears if you bury your foot to the floor when starting. You should get about 10.5 litres/100 km fuel economy with normal driving.

Should I be thinking about Lucas transmission treatment

Will this help the shift pattern