im asking if it affects anything in a negetive way to keep it on 4hi all the time, both on and off road.

 

If you are talking about dry pavement then no that will wear out your transfer case! Best to use 4wd in times when it's actually needed.

 

I would have to guess it effects your mpg and ups the wear and tare on the various parts that control 4 wheel drive. I have to ask, why would you want to run 4 high all the time?

 

Your truck will perform unpredictably and perhaps dangerously on dry hard surfaces such as asphalt as a consequence of the driveline binding. Eventually, it will simply break.

 

I do when there is snow or ice on the road but otherwise I never use it on dry pavement

 

Regular 4 high should not be used on dry pavement.

But the late model, high end F150s have an additional 4 auto mode. This is an on-demand all-wheel-drive move that can be left on all the time on all surfaces. It is said to reduce gas mileage to some degree (but I've never seen an amount listed) and my personal experience with my 2012 Lariat is that: (1) It really help keep the back wheels from spinning when making a fast start, and (2) it makes the ride subtly rougher as the system constantly adjusts the torque balance between the front and rear axles.

 

thanks for the responses. I asked because i often need 4wd , as where i live has a lots of steep off road hills i drive thru every day, so i have to keep switching to 4wd a few times a day, and sometimes i forget to turn it off......

 

Just keep in mind that when turning in 4wd, your inside front wheel must be able to slip, since it is trying to go the same distance as the outside wheel. Any surface that does not allow slippage will bind the drivetrain.

 

Eventually you will cause permanent damage, either in the drive shafts, joints, or T-case, none of which are cheap to fix. Just be careful and you'll be fine.