I know this has been discussed before but... I have been running Canadian Tire mid grade 89 Octane no ethanol since I picked up my Hemi and the wife filled up with 87 at some back road no name gas station. What to do? I've read it will only result in crappy fuel mileage or MDS not working properly. As a third of the tank has already been used, I'm considering topping up with 94 octane and emptying the tank and refilling with 89.. Any ideas??

 

Drive it.Lots of posters run 87 all the time.Lowers timing a degree or two.You won't notice much if anything different.

 

ive used both and dont notice a diff between the two

 

I ran a few tanks of 89 through and didn't notice any difference in milage or power. Just use the 87 now.

 

I do notice a difference in MPG.Not much but its lower running 87.

 

Have seen a few cylinder failures in Hemis and in every case the owner was running 87 octane fuel REGULARLY! Have also seen Hemis with 150k on them where the owner has never run anything BUT 87 octane.

So, REGULAR use of 87 increases chances of engine failure, but does not guarantee it. Pre-detonation often occurs and that is not a good thing on an engine on a regular basis.

However, this is WITH PROLONGED USE. Would I panic of I was on the road and only 87 was available? NO. Would I use 87 octane regularly? NO. One tank ain't gonna kill you. I just wouldn't tow a 5000k trailer with it in there...

 

Thanks guys.. will run it through.

 

Manual for the 2009 says this - which I read to say if it ain't knocking then you don't have to use 89 octane.

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.

 

I could give a rat's a$$ what the manual says I know that in EVERY case I've seen a failed compression test or a dropped piston in a modern Hemi, the owner either admitted to running 87 octane on the spot or 'fessed up to it later. And unless you are hooked up and monitoring for it, there is NO WAY of knowing if there is a pre-detonation happening unless it's severe if you are hearing a knock, you are causing irreversible engine damage.

Run you your 87 octane fuel every tank full, odds are you'll never have an issue, but nothing you can say or show in a manual will have me believe that the CHANCES of a major engine problem is not increased. I've seen what pre-detonation does with my own eyes... Going down a one way street at 90 mph doesn't mean you'll have a head on either, but I like my chances better if I was heading the right way. LOL...

Personally, I think it's VERY irresponsible of Chrysler to even put that in the manual. They are in essence leaving the burden of being able to tell if there is sufficient ping or knock or pre-detonation on the owner of the vehicle! If you design an engine that performs at peak efficiency at 89, then either state that 87 octane is NOT to be used OR design the thing with stereo knock sensors and a tune that will pull timing when necessary!!!

 

Ive tried it with both and DO notice a better gas milage with 89. Dont notice a power difference though. Here on out Im going to run 89. I jsut feel I spent alot on this truck and love my trucks whats an extra $10 or so in gas compared to this specific setup (09 10) possible failure.