Is using 5th gear at 40mph messes up my engine?

[Kal-El]

Originally Posted by Syroyizhka

I was driving with my friend the other day, and he yelled at me for using the fifth gear when i was going like 44 mph, I usually use it after 40 mph if driving on an even payment, however if its slightly up the hill I use 4th or even 3rd. He claims that he only uses the 5th on his Scion after 60 mph. Should i listen to him? cuz i think the manual said after 45 mph it was alright to use 5th. what are the most fuel efficcient speeds to change the gears, considering you're driving on a even payment?

Sorry, but your friend knows nothing about cars. Being in 4th at 44 mph is actually starting to rev your engine higher than it should while cruising on flat ground. Keeping it in 4th until 60 (in a 4 cylinder car) is now racing your engine and should only be done if you need hard acceleration or actually going almost 60 uphill. So, if your just cruising on flat ground, you should shift into 5th after 40 mph for optimal mileage and the least amount of engine wear.