My Mercury Mariner 2005 SUV takes regular gas. Can I use mid grade or premium gas? Would doing that harm the engine?

i don't really think it would ? if any thing it would be a bit more expensive but i will pretty much save your fuel pump in the long run i have a 87 t bird i converted it to preimo fuel i can get 300miles to 1/4 tank of gas, when i had it on regular it would suck back 1/2 tank going 150miles , this is the oldest car i have in my yard ans it runes better then all my newer models never had to go to the shop ever i think this will clean out any old regular gas in ur cars tank and and give you a bit more mileage :-) i have a 01 navigator when i bought it i filled it up with the high grade stuff it said on the compus system 250miles till empty ? Not good, from Edmonton to the Yukon a 2 day drive, i kept using premium by the time i finally got home after filling up with premium all the way it now ways 780miles till empty i liked those odds

premium will burn faster yes, it is a "higher percent of alcohol" in turn being cleaner, so if you use a better grade fuel you save in the long run in filters and components, however is more costly. To explain why there is a difference is simply that types of cars are designed to operate differently, most cars, as in everyday commuters have (pending location), 87-89-91-93-97, etc. those are fine, however, in the Ferrari, or (highly tuned machines), they don't like to run on them, the engines are designed for very high octane, if you were to use a gas that your car "didn't like", it would let you know by the engine knocking, or vibrating badly, that is for the most part all you would experience, but can do harm, in the long run to the sensors..i always tell people use what is recommended, the companies invest millions to figure out what works best, and we are not as smart, so why would we try to be.....same with engine oil, USE REGULAR, not synthetic, etc....hope i helped :)