I filled up with 93 octane premium last night. I'll see if I notice any difference.

The manual says to use 91, but my only choices are 87, 89 and 93.

Can I mix 1/2 a tank of 87 and 1/2 a tank of 93???

Not recommendable, because that could confuse the gas sensor and cause a problem. If you want to use lower than 90, use an octane booster, I recommend using premium fuel because the engine runs better and will have a longer life and efficiency.

it wont "confuse" anything. There is no "fuel sensor" that detects the octane level.
the knock sensor detects knock, and nothing else. if it doesnt sense knock, you have nothing to worry about.
if you drive in extreemly cold weather, 87 octane may indeed be enough as detonation will decrease quite a bit with the increased air density.
but in normal driving, 91 (or better) octane is recommended.

I've done a lot of reading and research on this and found that here in California the possibility of carbon build up if you use lower octane (decent) fuel is remote, if at all. Now, using your brother-in-law's gas he had back in the barn for 10 years might cause a problem.

Modern engines will automatically compensate for lower octane to reduce the pre-mature explosions (aka: knock) in the piston chamber. But, the engine will not run as designed and will not perform to it's highest potential.

I don't understand why it is called premium and why it costs more. Additives? I guess. But, I got my Endeavor for the power/torque (well, for a few other things, too). The new Outlander almost has as much "power" (220 hp to 225 hp) as the Endeavor, but the Endeavor has 255 for torque to the new Outlander's 204.... using premium gasoline, of course.

Anyway, I'm following the manual's recommendation. My two cents and a half... this week. Next week it'll be three cents.

Yes, I have an Endeavor 2004 with 65,000 miles and I am running 93 oct with an octane booster (4+) = 97 octane. If I start out in the morning and drive I have no pinging. But when the temperature of the day goes up say 80 deg and I sit and idle for 10-15 min, after that the engine will not stop pinging no matter what.

Do you know about the TSB-05-13-002 PCM Reprogramming for spark knock/Engine pinging/MFI DTCs /Delayed A/T shift? Does it help?

Please contact me
rebrokrfl@aol.com

It can only retard it so much.

why are you using 93 octane and an octane booster? thats completely unnecessary. of course its going to ping. i doubt the ECU can tune the timing in occordance with 97 octane. use 91 (10 gallons 89 + 10 gallons 93).

Please don't be misled in the slightest by all these people telling you that regular gas will screw up your fuel injectors, or mess with your OBC. It's horsecrap. I called Mitsubishi. They said that you CAN NOT DO ANY DAMAGE TO YOUR ENGINE using 87 or 89 octane gasoline. The only appreciable difference in not using high octane gas is a potential decrease in performance. I asked the tech to elaborate on what performance elements would be affected. He told me that you may experience slight decrease in acceleration responsiveness and nominal decreases in gas mileage. He also stated that this would be hardly noticeable, if noticed at all by the driver. The OBC is default set and tuned to 91 octane, but adjusts the fuel injection and ignition distribution for any octane at or above 87. Again, MITSUBISHI ASSURED ME THAT USING LOWER OCTANE GASOLINE WILL NEITHER VOID YOUR WARRANTY OR DAMAGE YOU VEHICLE IN ANY WAY.

just read the entire forum and there are few stating that they get around 2miles per galon by running premium gas. the car is supposed to hold 21 gallons,
lets use 20gallons as nobody should be pulling in the gas station empty ;)

20gallons x 2miles extra per gallon = 40 extra miles to the tank.

40 miles = $7-$9 of cost depending on your driving and gas prices..

this is based on the people stating they get 2miles more per gallon....

When I tried it after the 3 or 4th tank the engine had a lot of ping & knock

Is that what that smells from lol? I just bought my endeavor 5 days ago so i'm just figuring these things out, i noticed that premium grade was recommended but i would think most cars would say that. I've been using 87 octane but might switch now...

I got my Endeavor a week ago tomorrow. The dealer filled it with what I assume was regular. I've been doing a lot of city driving to get used to the feel of the vehicle, and was at half a tank around 125 miles. I filled it, from half, with 93 octane, and was at 150 miles at the half tank mark from almost all city driving. I'll let it drop to a little under a 1/4 tank and fill it again with 93 octane. I'm still getting used to the accelerator and tend to make a lot of quick starts, but it does seem to have a little more pickup now, as opposed to when I was test driving it, and when I took it home for the first time.

Well I have been reading everyones post and decided that even though I am sure someone will refute I will share my personal experience. I have a 2wd 04 Endeavor, I too was confused about premium or regular. I began with premium and made my way down as price of gas has gone up. At 86k running on regular I have maintained in mixed city and highway 22mpg on regular. I don't have any pinging I barely feel the power difference. When my timing belt, sparkplugs, and water pump where changed the mechanic noted how well my truck has been maintained internally in the engine and body. I admit I am religous with my oil changes at 3k and once in awhile put that chevron injector cleaning in the tank. My driving habits have changed drastically, I would normally drive 80-95mph on the highway and now I top 70mph, I don't jack-rabbit, I shut the engine off when I am waiting in a drive thru or long light, when I see the light turn red I let go of the gas pedal, on the highway I try to get behind a closed trailer semi by two car lengths. I learned many of these techniques from the hypermilling forums but I am not hardcore as they are, and it's been a struggle keeping my foot light. While visiting San Antonio where I originally bought my suv a day after she bought her endeavor XLS and she told me she only runs regular and she has had no problems with her endy. I also have a friend who has an 04 Lexus GX with 54k and Lexus recommends premium and she has only used regular and she has had no ill effects. Even Mitsubishi Motors of America has said regular is acceptable with no ill effects to the engine both short-term or long-term.

you will loose anywhere from 10 to 25 hp if you use regular unleaded.
you will probably also loose mileage.


you will not damage anything.


HOWEVER..... the car was designed for premium, and you should use what the engineers recommended. If you cant afford the extra 3-4 bucks per fillup, you probably shouldnt be driving in the first place.

I've run my Endeavor for four years on pretty much all 89 octane with no problems.

Certain brands of gas in the USA have a better detergent package (search top tier gas) that was developed in cooperation with some car manufacturers to address engine deposit issues.