Just got a 2010 "rental return" used SXT Journey. I really like it, as it is smaller than my Town and Country, and bigger than my PT, which it replaced (I now find I need only one car, and this is it.)

In spite of many negative reviews in the press, I find the ride comfortable, and I think it looks much better than the Pacifica, which looked too much like an old Plymouth station wagon (to me).

My question, though, is, with the 3.5L engine, "87 octane acceptable, 89 octane recommended," in the User Guide.

Does anyone exclusively use the 87 octane? Or, does anyone exclusively use the the 89 octane?

If there is a compelling reason to use the 89, I will, but if there isn't, I won't!

 

Chrysler is the only one doing this, they do it with a number of other engines, including the Hemi as well. The engine is tuned to run on 89 octane fuel, but there are knock sensors that are supposed to "de-tune" the engine (retard timing, etc.) when knocks/pings are detected, allowing the use of 87 octane fuel.

When using 87 octane, performance is decreased, fuel mileage will suffer somewhat, but supposedly it's safe to run the car.

I've found a good percentage of Hemi engines with failed cylinders (piston damage, scored walls, etc.) are engines that have run 87 octane fuel primarily. There is no data available on the 3.5L engine, it's just simply too new.

Like the Hemi, the 3.5L V6 has a very high compression ratio at 9.9:1. I've done quite a few engine build-ups in the past, worked at a performance shop as a side job some time ago, and the rule of thumb has always been 87 octane for compression under 9, 89 octane for compression between 9:1 and 10:1 and 91+ for anything over 10:1. At 9.9:1 the 3.5 V6 is almost to where it would call for premium gas! I dunno, I just don't like or really trust the fact that the engine must "sense" the lower octane fuel and then "de-tune" itself.

I think Chrysler has adopted this approach so as to not lose sales to people who simply don't want to spend the extra couple bucks a tank for higher octane fuel at a sacrifice to performance.

BUT, gas mileage should increase enough by using 89 octane gas to at least offset the price difference between the low and mid grades.

Personally, I'd use the mid-grade, especially if I planned on owning the car long-term...

 

Thank you for the detailed reply.

My PT had a "turbo lite" enigne, to which I added a stage one, so I used premium only after that (and got a real "kick in the pants" if I ever floored it!).

So, I am used to paying the premium price. Now that the (91 octane) PT is gone, along with my (87) Town and Country, it's OK with me to use the 89 octane on the Journey, as long as I know why I'm doing it.

And now I do!

BTW, I like your Lee Trevino quote!

 

So.... My 2011 Journey (in transit) with the Pentastar 3.6 should take premium at 10.2:1 compression?? Hopefully the extra mileage is worth the extra bucks!!