Accidental fuel mileage/power discovery

[mstocks]

I spent Thursday and Friday driving my new to me 80 series to Atlanta from Denver. I stopped in Podunk, IL ( I think that's what the city limit sign said) to gas up and found a station who's corporate name I recognized. Can't remember what gas company, but that's not too important to my story. I pulled up to the pump, got out and noticed that the three options were 89, 90 and 93 octane. Quite odd to me as I have never been presented with these options before.

Following the advice of several cruiser buddies who told me that the 80 series prefer 87 octane, I opted for the 89. Over that tank of gas, running around 72 on cruise, with roof rack catching all the wind it could, I got almost 14 mpg. Not only that, but she hardly downshifted going uphill with the cruise set. I would drop to 70 or 71, but no downshift. Power and throttle response seemed much better than the 2 or 3 previous tanks.

Anyone else ever noticed this? I am curious if the interstate exercise of 6-700 miles at 60-70 mph helped and it was pure coincidence or if my truck is going to prefer 89 octane fuel. I ran 2 tanks of 87 after this and still got around 13 but that was with some traffic, less cruise control and some stop and go (tornado clean up in Tennessee).

I'll keep experimenting and I need to replace the plugs/wires and distributor. Maybe my mileage will get even better. I'm not too concerned as I didn't buy the 80 for it's mpg, but every little bit helps. The roof rack is going to live in the basement for now, so that will help too.

 

[bpassmore]

anything between 12 and 16 can be "normal". Don't try to get too scientific with it, as you will go crazy and waste your time... - Not to diminish what you are doing, but these numbers vary widely from vehicle to vehicle.

Just revel in the fact that you drive an awesome rig with incredible capabilities straight from the factory.

 

[cartercd]

I doubt that the octane made any difference. An engine that is designed to run on 87 octane will not run any better on 89, 93, or even racing fuel. If the engine is not knocking, then increasing octane will not help you. Higher octane may be warranted if you have modified the engine (advanced the ignition, add a turbocharger) or if it is under a heavy load and knocking.

The difference in mileage you experienced was probably a result of changing conditions. Congrats on your new Cruiser.

 

[dgangle]

I doubt that the octane made any difference. An engine that is designed to run on 87 octane will not run any better on 89, 93, or even racing fuel. If the engine is not knocking, then increasing octane will not help you. Higher octane may be warranted if you have modified the engine (advanced the ignition, add a turbocharger) or if it is under a heavy load and knocking.

The difference in mileage you experienced was probably a result of changing conditions. Congrats on your new Cruiser.

Amen. The only benefit of using a higher octane fuel than what the manufacturer recommends is only superficial. Increased octane only benefits pre-denotation for a higher compression engine.

 

[TwoTonic]

Another factor, as you were in the midwest, is that often the "89 or 90 octane" fuel is 10% ethanol, whereas the 87 octane is straight gasoline. Even though the 89 octane is less prone to pre-detonation, frequently the LOWER octane grade will deliver better mileage, since the added ethanol has less energy per gallon than gasoline.

Not sure it's relevant, but particularly in the midwest there's a lot of ethanol used to raise octane and to keep farm state congressmen happy.

 

[HntWhtTail]

There are hills in IL?? I have found that 72 on the speedo, produces better mpg than 65, because I am at higher rpm and carry more speed over hills less down shifting. I have been averaging 13 commuting to and from work. and have yet to go over 14 still trying...

 

[finderscuba]

Wind will make a huge difference as well. Case in point: last summer we drove from Winnipeg to Vancouver Island in my wife's Golf TDI. It was fairly windy on the first day of driving across the prairies. We averaged about 35 mpg on that first day. Once in the mountains (Calgary through Vancouver), we averaged about 50 mpg.

Prairies: speed was about 110 km/h, had headwinds and ambient temperatures around 20°C, no AC, loaded car with roof rack and roof box.

Mountains: speed was about 120 km/h, no particular winds, ambient temperatures between 25°C and 38°C (yes 38!! in the Okanagan), AC on almost continuously, same load in and on car.

I blame the wind. I've had similar issues towing a trailer into a headwind - can actually watch the fuel gauge drop - pedal to the floor to maintain speed.

 

[Jim_Phillips]

I am with you on the MPG fascination. I get 26-28 with mine since it is both diesel and manual transmission. I still like to drive for economy but don't fuss too much over the numbers. At the end of the day it is depreciation that really costs you - the difference between 14 and 20 mpg is marginal compared to leasing a newer fuel efficient car.

 

[thisilldefend]

I am willing to bet on the old British Thermal Units (btu's) in the gasoline made the differance. I have lived in states where you have no choice but to get that corn stuff in the tank. I hate ethanol. I want good old fashioned fossil fuels. And I plan on burning a tanker full when I get home.

 

[webster2001]

My wife and I picked up our 97' TLC in Santa Clarita, CA on the 4/2/2009 and took I-40 back to Atlanta. Averaged 16.2 MPG on the 2300 miles back home. 18.3MPG was the best 14MPG was the worst. 70-75MPH.

Don't read into the numbers too much when it comes to mileage. These beauties were not built for MPG they were built to go where no current sissy car based SUV dares to travel.

This is my first TLC, but not my first fuel thirsty truck