Dear Tom and Ray:
Hello from Germany. I am a U.S. service member stationed in Germany. My job location has recently changed, and I now have to drive about 35 miles to work (one way) each day. As you know, the Autobahn in Germany has no speed limit in most places, and it's embarrassing to constantly be passed by VW Rabbits! I own a 1997 Dodge Intrepid with 60,000 miles. It has a 3.5-liter six-cylinder engine. The car's tachometer has a red line of 6,500 rpm, and it will travel at 100 mph at around 3,200 rpm. My question is: Will it hurt my engine (or any part of the car) to drive to work at high speeds every day? I usually drive between 90 and 100 mph. I have new tires that are rated for these speeds. At what engine rpm should I be concerned about causing damage? -- Mike
TOM: Anything above 0 rpm, Mike. We've found that at an rpm of 0, engine damage is extremely rare -- though not unheard of if my brother is working on the car.
RAY: Actually, there's not a clear answer to this one way or the other, Mike. We know that accelerating quickly is very bad for your car. But the case against simply driving fast -- once you've accelerated -- is less clear.
TOM: On one hand, this car was clearly designed to be able to cruise at 75 or 80 on American highways. So 90 isn't that far a stretch for it.
RAY: On the other hand, the amount of wind resistance you get at those speeds requires the engine to work very hard. And while the rpm might be within acceptable limits, you're making the engine run hot because you have the gas pedal very close to the floor. It's as if you were constantly climbing a hill.
TOM: And that strains everything, from the connecting rods all the way down to the axles. Over time, you will wear out your engine, transmission and drive train faster that way.
RAY: Will driving it at 100 mph for a day, a week or even a few months ruin it and cause it to stop dead in its tracks, or roll over with its tongue hanging out and all four wheels in the air? It's unlikely. But it's not a used car I would ever want to buy. And it might not be one you want to own later in its life, Mike.