I've always been told that running your engine hard is bad. I understand its pointless to operate in a lower gear than necessary. But on the highway is it necessarily harmful to cruise at 4000-5000 rpm? How much wear and tear does that actually put on the engine/transmission. (I'm not asking if its bad to accelerate through gears at high rpm, just asking about highway cruising.)

Thanks.

 

running at high rpm isnt intrinsically bad for your engine so long as you arent too close to your engines red line. The only thing you need to watch out for is overheating your engine. so make sure you keep an eye on your engine temp gauge and keep your fluids from getting too low.

In terms of highway driving its stupid to run at those rpms if you can shift up to another gear because you just wind up burning more fuel needlessly. If you are cruising at a constant speed your tach should never read more than 3000 rpm regardless of where you are. Again this is not because of wear and tear on your engine it has to do with fuel efficiency. (This is more 95% of cars in 99.9% of driving situations)