You better read your owners manual again!!! From the 08 owners manual.

FUEL REQUIREMENTS
87

All engines (except 5.7L engines) are designed
to meet all emissions regulations
and provide excellent fuel economy and
performance when using high-quality unleaded
“regular” gasoline having an octane
rating of 87. The use of premium
gasoline is not recommended. Under normal
conditions, the use of premium gasoline will not
provide a benefit over high-quality regular gasolines, and
in some circumstances may result in poorer performance.
89

The 5.7L engine is designed to meet all
emissions regulations and provide satisfactory
fuel economy and performance when
using high-quality unleaded gasoline having
an octane range of 87 to 89. The manufacturer
recommends the use of 89 octane for optimum performance. The use of premium gasoline
is not recommended. Under normal conditions, the use of
premium gasoline will not provide a benefit over highquality
regular and mid-grade gasolines, and in some
circumstances may result in poorer performance.
Light spark knock at low engine speeds is not harmful to
your engine. However, continued heavy spark knock at
high speeds can cause damage and immediate service is
required.
Poor quality gasoline can cause problems such as hard
starting, stalling and hesitations. If you experience these
symptoms, try another brand of “regular” gasoline before
considering service for the vehicle.
Over 40 auto manufacturers worldwide have issued and
endorsed consistent gasoline specifications (the Worldwide
Fuel Charter, WWFC) to define fuel properties
necessary to deliver enhanced emissions, performance
and durability for your vehicle. We recommend the use
of gasolines that meet the WWFC specifications if they
are available.

 

also another problem that will lead to this is not running the truck hot long enough i know dodge has had problems with this such as the sprinter van if it idled in traffic to long it would ruin the engine by not burning off the excess grim my dad who works at a dealer says you need to take it on the highway at least once a week for roughly 20 min to get a good burn off of all the grim but i might have to start running 89 in it after seeing this thread all i ever put is 87

 

run 89 instead of 87. unless you are on a 91 or 93 tune, then run that. but otherwise, enough have stated that it is worth the 3 bucks or whatever more for 89. As i stated before, I had predetonation on 2 cylinders from running 87 one summer. blew a hole in 2 pistons. Dealer even said, after they covered it under warranty, run 89 all the time no exceptions. anyone else wanna have to pull their engine at 57,000 mi? I dont.

 

I'm glad I saw this thread. I had no idea that 89 was recommended for a 5.7. I read all this and then checked my manual for conformation. I ran 87 for the first 23K in my truck. I filled up earlier this week with 89 and saw a .6 MPG increase and it seems the truck runs better. I'm using 89 from now on. Mayble my MPG's will get a little better, but I don't have very high expectations. haha. Thanks for the eye-opener!

 

Is 93 bad for the engine without a tuner?

 

No, not at all. You may see no benefit over running 89 or 91 octane, but it's fine...

 

Thanks for the fastest reply ever!

 

I would actually recomend changing your plugs early because of this. You should notice a difference right away. At least pull a plug and see how it's doing. (when the engine is cold)

 

I totally agree with dog on his logic. I run 93 in my 4.7 every time. it only makes about a 4 dollar difference because my fillups are usually 20 gallons and the difference from 87 to 93 in Pa where I am is 20 cents. I ran 87 when i first bought the truck but one day it threw a cel for a rough idle and it didn't feel right and i got really really really ****ty MPG's like 10 mpg that tank so i figured I got bad/watery gas at the station and it messed with my baby. so now i run 93. I don't really see a noticable performance jump or MPG but it's piece of mind that the gas my truck is getting is good. and like dog said if you are worried about 4 dollars when you're spending 40 plus on gas then you should have never bought a truck to begin with.

i can't confirm this but I have heard that the higher octane fuel anything above 87 does not have ethanol mixed in with it. which i'm totally cool with. ethanol blows. lower heat of combustion meaning that for each gallon of fuel you get less out of it so your mpg decreases and so does the output in power that the vehicle creates. not to mention ethanol is a alcohol with a polar hydroxide group attached to one of the two carbon...... polar compounds attract and will mix with gas which we all know is bad

 

damn, glad i read this thread, up here they sell 85 octane, which i've filled up with twice now. looks like i'll be buying premium now since it's 89 octane! i'd rather pay a few cents a gallon than the cost of a new 4.7 engine.