87 Octane or 89 for the HEMI? - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 13 (permalink) Old 12-07-2007, 09:04 AM Thread Starter
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87 Octane or 89 for the HEMI?

Due to the gas price I have been putting 87 octane in my Hemi and I know the manual recommends 89 will I dammage the fuel sysytem in the long run? I would like to know how many members run 87 or 89 octane in their Hemis?

06' Black Limited QDII HEMI - 2" Revtek Lift 245/75/17 Goodyear Duratrac -Monroe Sensa Trac Struts and Sensa Trac Load Adjusting Shocks.
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post #2 of 13 (permalink) Old 12-07-2007, 09:38 AM
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Damage the fuel system? No. Run like crap and get worse gas mileage? Yes.
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post #3 of 13 (permalink) Old 12-07-2007, 09:50 AM
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If you calculate the difference, it's only 2-4 dollars per fill-up.

I run 89 Octane in mine.

Later, TexasHemi

06 Commander Limited - Hemi, K&N Cold Air Intake, Magnaflow Muffler, NGK Platinum spark plugs, 245/65-17 Bridgestone Revo's

08 Passat 2.0T
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post #4 of 13 (permalink) Old 12-07-2007, 10:27 AM
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If you dont hear the engine knocking I doubt the 87 will hurt it but as pointed out above probably you will get slightly different (lower) gas mileage. Personally, for the difference to me as I dont drive long distances except on a trip I just use 89. So you know, places like Chevron put in more cleaning agents the higher up the octane grade you go. john
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post #5 of 13 (permalink) Old 12-07-2007, 10:27 AM
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87 octane will give you worse gas milage than 89 octane. Whether it's wort it too you to run the cheaper gas depends on the percentage difference of the gas mileage.

For example, if you normally average 15 mpg with 89 octane and get 14 mpg with 87 octane, the difference is about 7%. Where I'm at, 87 octane is $3.00/gal., 89 octane is $3.13/gal. At 7% difference, 89 octane would have to cost about $3.21/gal to equal things out with buying 87 octane. Although 87 octane looks cheaper, in the long run it would cost you more.

John
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post #6 of 13 (permalink) Old 12-07-2007, 12:12 PM
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I have used 87 in mine since it was new and it runs just fine. I did try a couple of tanks of 89 to see if the mpg improved but it didn't.

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post #7 of 13 (permalink) Old 12-07-2007, 12:40 PM
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Owners manual says to run mid grade, which I guess is 88 or 89 octane depending on the altitude. There was a thread or 2 on this awhile back where someone actually explained why it mattered. I tend to run my vehicles to 150K-200K before getting rid of them so I tend to be more careful on following operating/maintenance recomendations as it is generally down the road that poor maintenance, bad fuel will have an affect. If your gonna run it till 50K & sell it, then it won't matter in fact you can water the fuel down to get better gas milage (just kidding). But if you want it for the long haul then it will effect it either in engine damage or higher repair costs eventually.

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post #8 of 13 (permalink) Old 12-07-2007, 12:52 PM
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From the Owner's Manual (2006):

FUEL REQUIREMENTS
3.7/4.7L Engines (If Equipped)

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.


5.7L Engines (If Equipped)


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 high quality 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 gasoline before considering
service for the vehicle.


2006 Steel Blue 5.7L HEMI Limited 4x4 Build Date: June 9, 2006 Hour 14
Interior: Dark Slate/Light Graystone with Saddle Brown Leather Seats
Quadra-Drive II, NAV, DVD, Trailer Tow Group IV, Off-Road Group II, Remote Start, UConnect, Rear Backup Camera, Chrome Wheels,
Magnaflow cat-back exhaust, Daytime Running Lights enabled, 2" Rough Country Lift with 265/70R17 Goodyear Wrangler AT/S

Last edited by jeep5253; 12-07-2007 at 04:39 PM.
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post #9 of 13 (permalink) Old 12-07-2007, 10:10 PM
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I have experimented with mine and I undoubtedly got better mileage and performance on the 89. You are not saving anything by running 87 based on how my Hemi runs. As mentioned above. $2 a tank is worth messing arounfd with anyhow.

06 Commander Limited 25H: Dark Khaki, QD II 4WD, towing group IV, 5.7L Hemi, AEM CAI, Jet stage 1
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post #10 of 13 (permalink) Old 12-08-2007, 02:08 AM
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Damn, I guess my next few tanks will be 89 and not the usual 87 I run because I'm cheap! Damn numbers.

RIP - Silver '06 Limited; 5.7 Hemi; 2" TerraFlex Lift; 255/70R17 Bridgestone Dueler REVOS, Horizontal Inclinometer, Signal Frog Antenna Ball, Surco Safari 50"x50" Roof Rack, GetLost4x4 bumper, Bulldog 9k Winch, GetLost4x4 Rock Rails - (should have added a snorkel)
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