Just getting into a 2018 3.5 ecoboost used almost exclusively for towing an enclosed 7000 lb. car trailer . Everywhere I go there are hills involved. I know the manual says regular unleaded gas which I assume means 87 octane, what should I really buy? 87? 89? 91? Does any body experimented with the various grades and gotten better performance/gas mileage. I assume the knock sensors would keep me from damaging anything with 87. thanks.

 

The manual actually tells you to use higher octane when you are towing.

 

My 13 manual says use premium when towing. I see a couple mpg improvement but not enough to justify the cost. The justification for me is that the throttle response seems much better. I don't drive a ton so I usually just run premium in it all the time.

 

Yeah, the knock sensors will prevent engine damage, but they reduce power and torque when they sense you went cheap with the gasoline.

On my 2012 with 3.5L EcoBoost engine, after thousands of miles of towing, I calculated that towing with premium gas just about paid for the extra cost of premium, and gave me more power and torque for climbing hills and passes, and the engine ran cooler and better. So I always tied to plan ahead and be near empty when I filled up with premium gas for a towing trip.

Octane varies with altitude. Here at about 2,400 feet, most premium is 91 octane. In "mile high" Denver it's about 89. Only in the flats near sea level will you usually find 92 octane premium. But octane doesn't matter as long as it's high enough to prevent knock. Stick with the major bands of premium gasoline and you should be good to go with premium at any altitude.

 

the power difference between 87 and 93 octane is quite noticeable. The higher octane allows the motor to run more optimal ignition timing at lower rpm, delivering more power and efficiency than on 87, thereby a better towing experience.