87 vs 89 octane fuel

[jeepkj02]

Recently, I have gone to some gas stations and 87 and 89 octane are the same price. Will I get better gas mileage or performance if I put in a higher octane, or will it blow a head gasket or something!!??

 

[Marlon_JB2]

No and No.

 

[jeepkj02]

D'oh! #-o

 

[Corwyyn]

You probably wouldn't notice any difference at all. A buddy at work was complaining that he went a couple of tanks with 91 octane in his car instead of the standard 87 and got worse mileage. If your car wasn't specifically designed to need high-octane fuel then you're just wasting money you could be using to mod the Jeep :-s

 

[jfortier777]

I've been told that every now and then you should run some premium through on an empty on the premise that it burns hotter and cleans out the engine. I have no evidence of this, but I do wonder if there is any truth behind it.

BTW - Using the wrong gas can void your warranty. Or so I hear.

 

[jeepkj02]

If your car wasn't specifically designed to need high-octane fuel then you're just wasting money you could be using to mod the Jeep Eh?

As I said in my original post, in some gas stations it is the same price as 87 octane...but if will decrease my gas mileage its not worth trying.

 

[jeepkj02]

BTW - Using the wrong gas can void your warranty. Or so I hear.

I don't have to worry about that. It's an 2002 with 68K miles. I don't think I have any warranties left...

 

[Marlon_JB2]

You might have some powertrain warranty left. I'd check with the dealer. And in that case, you really shouldn't be running the wrong fuel.

And *yes* some manufacturers can void your warranty for running the wrong fuel. I don't think DCX is one of them though.

 

[papercut]

The owner's manual for my '06 says the following (I'm summarizing):

1) Designed for and runs fine on 87 octane.

2) Don't bother with premium, you probably won't see any difference.

3) 89 octane might help with milage when towing a heavy load or in hot weather or a few other circumstances.


That said, I've been experimenting with 89 octane, and it appears to me that it's helped my milage a little bit. Not leaps and bounds, but just enough to where I think it matters. Specifically, I'm getting 19.5-20 MPG on 89; with 87, I seem to get about 17.5-18.5. I'm currently experimenting with the following fill-up rotation: 89-87-87, 89-87-87 (lather rinse repeat). It *seems* that, with the first tank of 87 after the 89, it's easier to keep the higher milage figure. By the end of the second tank of 87, though, my milage tends to drop a little. Still need to do some more experimenting, though.

So, my thought is, if both are the same price, go for the 89. It won't hurt anything.

 

[jeepkj02]

Try it out next fill, just filled up (1/2 tank) yesterday. Will post improvements (if any).

 

[jeepkj02]

I also heard that you could but some diesel in the mix. If so...

What type of diesel? (B-100, B-10, B-15..)

What sort of mix? (10/90%....)

What will this do? Has it caused problems?

 

[Dave]

Papercut is correct...............His 06 manual says the same thing that my 05 manual does. The 3.7 liter is made to run on 87 octaine.

I mostly just use 87 octaine but once in a while when towing I'll put some 89 in it. I can't really tell a difference but then i'm usually mixing it with 1/4 or almost 1/2 tank of 87 so I really don't have 89 - probably would have to put in 91 to mix with the 87 or wait until i'm almost empty and fill it with 89.

Anyway I don't think an occasional tank of a higher octaine is going to hurt it. Could be a waste of money if not towing??

One thing's for sure - it won't make a Hemi out of it..........hmmmmm a Hemi KJ .....I wonder what that would feel like?? Next mod anyone????

Dave

 

[raceinfan]

by running higher octane you could experiance some pinging which is not good I believe you could burn up the valves,& these engines are run & designed at the factory on 87 octane I have heard of guy's running a cleaner additive in thier fuel but I haven't tried it personaly there is some stuff some dealers use it's called BG I've had them put it in on my ram I used to own both fuel & engine treatment never had a problem

 

[papercut]

I also heard that you could but some diesel in the mix. If so...

What type of diesel? (B-100, B-10, B-15..)

What sort of mix? (10/90%....)

What will this do? Has it caused problems?

In a gas engine? You've got to be kidding me!

Engine damage aside, you'd probably be pulled over by the police for being a road hazard. I'm referring to all of the smoke that'll be pouring out of your tailpipe that will obscure the vision of everyone behind you.