So I've had my truck for about 3 weeks - have 2200 miles on it. (Laramie w/ 5.7 hemi)

When I bought the truck I asked the salesperson what fuel should be used - she said use the standard regular unleaded (I believe it's 87 octane). The manual says that the 5.7 is designed to operate in the 87 to 89 range of fuels but the manufacturer 'recommends' using 89, and, says you should not use premium.

So the obvious question - what fuel to use? Should I use the mid-grade which is around 88 to 89, or the regular. Since I live at a higher altitude (6500ft) does that make a difference.

Thoughts?

 

To put it simply, your engine is tuned for 89 octane and will perform best with it. But, it is also designed to 'de-tune' itself if knocking caused by a lower octane such as 87 is used. It will function fine, but will make less power and suck more fuel. It is not designed to advance the timing beyond the 89 octane point, so 91/93 is a waste and it won't perform as well as 89 does.

Being in high altitude, lower octanes won't detonate as easily, so you shouldn't have as much of a performance loss running 87 as us lowlanders would. That is if you can find 87, if memory serves me correctly, most 'regular' up there is 85, for that reason.

 

What inbred said is correct. You'll be fine running 87 and will only notice a difference between 87 & 89 when accelerating hard. If that's not a problem, then you can run 87. If you want maximum performance, run 89. But 87 won't hurt the truck.

 

They told me regular at the dealer too. The manual says 87 is acceptable and 89 is preferred. It seems like they are not really sure which grade you should use. If it needs 89 it should be marked on the gas cap.
I have run both 87 and 89 and have noticed no difference at all. The only real difference is when I run pure gas. No ethanol. I get about 1 mile better.
Pure gas is plentiful in our area, and I use it every chance I get.

For some reason I keep using 89. Its not logical. And I am quite logical on everything else.

Ps.....For the pros: If you are using one grade, should you stick to that grade? Or is it okay to jump from grade to grade?

 

Do not trust most salesmen with technical questions.

Follow the manual and use the recommended 89. If you tank is completely dry it will cost less than $3 to use it over 87.

 

it has nothing to do with 'not being sure'. It will run fine on 87. It will run better than fine on 89. They don't mark the gas cap, because it does not NEED 89. It just runs better with it. If you don't notice a MPG difference between the two, compare the two hauling or towing a load over a distance. You will. Knock conditions that would pull timing aren't really gonna show up under light throttles and loads. If you do unloaded highway driving, you probably won't notice a difference.

 

I use 89 and from the same company...Marathon! Probably better fuels out there but I like Marathon!

 

I just stick with the 89. I'm lucky though in that I only drive into the office twice a week and work from home the rest of the time. I also only live 10 miles from the office so I fill up once about every 3 wks or so. However, 94rt is right, don't let the #'s on the pump fool you. If the 89 is .10 or so more than the 87 you're only saving 3 bucks and that's if the tank is bone dry. I normally fill up at a qtr tank or so and I have the 27gal tank so it just doesn't make sense for me to use the 87. Jeff.

 

A related question:

When I bought my 2002 Porsche Boxter, the salesman told me to only buy Chevron gas. Not curious enough to question, I've done so and try to buy Chevron for all our vehicles.

(I don't know if my wife buys Chevron because, as you all probably know, most women think it's illegal in CA for them to buy gas. )

I did notice once when buying Shell that it is formulated with 10% ethanol. I'm pretty sure Arco (a cheapo brand) has ethanol. I can't tell you for certain because it was a while ago and I may have spotted a local situation. However, with that as a backbground, here's my question:

Do the gurus on this forum think there's a difference between gasoline brands--despite octane ratings (87, 89, 91) listed on pumps?

 

Yes there is a difference. Every brand uses their own detergents and additives to stabilize the fuel, to preserve it, and to try and decrease carbon build up in engines. In some cases these additives also help determine the octane rating. Except for the occasional water that can get into gasoline, i have never had any issue with any brand of gas. I cannot however vouch for everyone and every car brand.