corolla highway rpm

I drove my folks' '04 Corolla on the highway once. This was with a 4-speed automatic, and I think it was at 75mph where the RPMs were a steady 3000.

Needless to say, one should achieve lower RPMs at that speed in 5th gear.

You guys are far too used to high-torque, large capacity engines. My celica (2ltr turbo) runs 2800rpm at 75, in fact virtually every petrol car i have been in other than monster 3.5 to 4 litre ones have been around 3000rpm. Autos are different generally, my dads 3.5 auto sits at about 2200 at 70mph. 2800 rpm is the optimum fuel efficiency speed for a 2litre-ish 4 stroke internal combustion engine, hence why most manufacturers make highway speeds that level in 5th. This changes with engine size and the new VVTi setups but its still approximately correct as it is linked to the speed of combustion of the fuel in the cylinders.

J

I've driven a 3.9L V6 pickup truck for 8 years and 170k miles, and I admit I've really enjoyed it's super low highway cruise rpm... it turns around 2000 rpm in 5th gear at 70mph! This is mainly thanks to the

3.21 axle ratio. But the reason I like this low highway rpm is plain and simple: less engine wear per unit of distance driven.

I'm putting said truck into semi-retirement and getting either a Corolla or a Civic to start using as my daily driver, mainly highway... and I much prefer manuals to automatics, but if the automatics are keeping these little 4-bangers down closer to 2000rpm, then I might have to re-consider. 3000rpm vs 2000rpm is a 50% increase in crankshaft revolutions, which scares me a little.

Dont be scared, wear rate is not only a function of number of revolutions - its FAR more complex than that. The engine and transmission has been *designed* to work at that rate, just as the lower rpm engine has - its not the same as taking the same engine and running it at different RPMs. In actual fact to run the same engine slower but output the same power (the power required to maintain highway speed) would require more torque to be passed through the engine and driveline which would increase wear somewhat.

J

Just as a side note - fatigue failure and wear is a function of load and speed, but from what i remember its much more greatly related to load than speed of cycling - so ideally a well balanced high revving engine would last longer than a slow clunker with big torque.

Many automatics have taller gearing compared to their (more ratioed) manual counterparts.

Eh? How do you figure this?

Hmmm...

But the same wear rate on drivetrain components from final drive to the road...

As Coyoteboy has pointed out, this is a simplistic perspective. If the oil is providing the necessary lubrication you've nothing to worry about. Most wear is caused when the engine (and associated funkiness) is cold, or when the oil is shot - reduce cold starts and ensure you change the oil as recommended and it'll be absolutely fine. Labouring the engine at lower speeds is bad news for longevity...

65 mph = 2,500.