I have not been in a 3rd-gen RAV in a long time so I cant help there, but I can offer some advice in the form of an app that I use to track my mileage in my cars. It is called Fuelly, and I use this because this will give you a precise, accurate figure. The in-car MPG display is really more of an estimation, and on some cars they aren't that accurate. For example on the Subaru forums that reading has earned the nickname "exaggerometer"

 

You posted on the 3rd generation forum 2006-2012. What year is your car? Older RAV4 do not have this feature.

 

It might be on trip meter button.

 

Our 2006 RAV4 didn't have a mpg readout or a display button but our 2011 does. It allows displaying either instantaneous mpg which is pretty useless or average mpg. The button is on the steering wheel near the bluetooth & phone buttons.