Now this scenario is not me because I would never disobey the posted speed limits, but hypothetically...

If I did the recommended break-in and baby the car, BUT sustain high highway speeds for an 45 min or so twice a day, is it bad for the car? One of the reasons I got the car is the tall 6th gear. And I don't think the tach is much over 3K at 80mph.

I do treat the car well overall. I usually take it easy accelerating and keep the rpm reasonable. My experience and education tells me that hard accelerating and braking are what take their toll on a car, but I'd like your take on it to tell me if I'm not considering something. I want this car to last.

 

doesnt sound like that would hurt it. I have done more than that. I drove 1.5 hours at 90mph no adverse effects as to yet.

 

Driving at highway speeds is the most gentle use your car will see. It is much better for the car than stop and go conditions. Most cars with really high mileage on them are used mainly on the highway.

 

There is almost no load on the engine when cruising at speed, less than 15 hp is normal for a newer car at 80mph. At that output the engine will run nearly forever. It is the stop and go stress that put wear on an engines internals and even so if maintained it should run well over 100k miles w/o a problem. I know of a MB diesel that has 300k miles and no engine work at all! Three transmissions, but no engine work! The places where you will notice wear are wheel bearings and automatic transmissions. Keep it lubed and aligned and you will not have any trouble at all. Also, remember that MBs are designed for the Autobahn where speeds are in excess of 100mph in places for long stretches. This would kill most american cars but MBs eat it up!

 

Totally right, and that is why sellers always try to stress that their car has high miles "they're all highway". If they're honest about that, it does make a difference and should be a used car buyer consideration. Cruising @80 and 3k is definitely easy on the drivetrain, but maybe certain hardware like wheel bearings would show some faster wear I'd say but that's about it.

 

I always thought that Benz cars in particular were made to last. Engines and transmission are supposed to be solid and will outlive most cars. I just hope I don't regret saying that.

 

Don't forget the autobahn, where people commute to work at 120+ mph daily.

 

This is a little OT, but still: a car top speed calculator. For the C Coupe, for instance, if you plug in 192HP and 149MPH as the "old" values, you'll be able to see what power output will be required to reach certain speeds.

I tried it with a few cars with the same drag coefficients, and it seems to be fairly accurate.

http://www.rx7turboturbo.com/robrobinette/top_speed.htm