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.
The owner's manual recommends 89 for optimum performance but it will run on 87. I would choose the 89. I pasted below the text from the owner's manual.
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, as it will not provide any benefit
over regular gasoline in these engines.
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 gasoline
before considering service for the vehicle.