ok so I know that the manual says to use premuim gas and thats what I have been use except for the first two fill ups when I first got the truck. I noticed a drop in MPG when I switched to premium. What damage could or would been done if I go back to useing regular gas. I have the the 08 MDS 5.7L Hemi 4x4.

 

hemi uses midgrades as recommended gas and regular is okay. premium gas is recomended for srt10 trucks unless u have premium tune for it.

 

mine has no problems whatsoever with regular. don't make it a sudden change. switch to regular over a couple tanks. fill with reg when the premium tank gets to 3/4, then half, then quarter... that way your pcm can adjust for it. mine bitched for a day when i switched back to regular too quick, then it shut up and took it.

 

Manual says Hemi wants you to use the middle one, I use all 3, just never a full tank of regular. Last time i got a full tank of regilar the MPG went down, so i usually fill her up with plus, or blend plus and regular.

 

Yes 89 seems to be the gem for me as well. 87 just didnt give me good mpg. I always used 93 in my cars until this year, but they were older and needed it. My Hemi likes 89 though.

 

My 07 Hemi gets better mileage using 87.

Rick

 

Mine's obviously not a HEMI but I've used mid grade since I got mine cuz that's what the stealership said they fill her up with when I got it...

 

I was using 87 but then I noticed the manual recommend 89 so I switched. I (I didnt want to do anything that might void the lifetime warrenty) noticed that I now have to fill up more often then I did when I was running 87. This is why I was wondering if I can go back to using 87 plus its cheaper. So If if i slowly reintro 87 back into the HEMI I should be fine? This is my first vech with a HEMI so I rather not mess things up.

 

reg should be fine. it won't void your warranty. it's recommended not required.

 

I think you need to give regular and mid grade a test, since the trucks react differently. I'mtesting regular right now to see what mileage impact it might have. I think my manual specifically says they do not recommened the 91 octane though.