ScanGauge and Octane - Fuel Economy, Hypermiling, EcoModding News and Forum

mcrews · 08-08-2010, 05:09 AM

Recently (july 13-29) drove to Dallas from Sacramento and back. about 1750 miles each way. I dont travel 'light'. "Heck it's a 4 dr w/ a trunk.....why not fill it!!!" You get the picture.

I have had the sg for about a yr. It sits right in the middle of my gauges so it gives me instant info w/out looking elswhere.

The 02 Infiniti Q45 requires 91 octane. However, around town I didn't really care and ran 89 or 87. I tend to be a very 'mpg' kind of driver and didnt really notice a difference.

I hit the 'grapevine' (15 miles of climbing to get into the LA basin on I-5) at around 3:45 pm Temp was around 98 degrees. I had a tank of 87 octane.
The temp gauge on the SG got to 233`degrees. (I had installed a new themostat 180 degrees right before the trip. the car just hit 200k and I figured ....might as well) I started worrying because the car warning for OVERHEATING is triggered at 242.
I have driven the grapevine 8 or 9 times and never had an overheating problem before. The car also seemed to be 'slipping' or really trying to go faster.

Well as I was going down into the LA basin I hit rush hour and was stressing all the way for the next 2 hours. I stopped at a Pepboys and bought a 10 inch aux fan and a small trans cooler. Since i was headed into AZ and the high was 113 the day before I was really stressed!!!. I service the car very regularly and really try to pay attention to the little things.

Next morning I get gas, It was cheaper so I got the good stuff 91 octane. I still had not made the conection. As I was driving, though, I noticed the difference and started using IGN and LOAD along w/ TEMP on the sg. I got out the sg manual and read about IGN. Seem that the engine will advance or retard based on OCTANE and air Temp.

Sure enough, the IGN (TIMING) was running 29-36 and the temp never got over 207. On the next tank I ran 87 again but had picked up some OCTANE boost. THe IGN was at 21-27 and the temp was as high as 213.

WHAt did I learn: When traveling on the road alway run the best octane possible (they have 93 outside of CA!!!) WHen in town on short trips I can run midgrade everyother tank.

Other cars may be programed differently. I think there was a post that said octane did make any difference in mpg. But given that my car requires it, running anything less, especially under a load seems to make a difference in performance.

talldudenumber5 · 08-08-2010, 12:49 PM

i have a 96 maxima and like all good nissan's / infiniti's i am supposed to run 91 too. i can tell a small differance even without a scan gauge between low grade and high grade gas. but maybe this lesson can be carried on. maybe 89 91 durning the summer and 87 durning the winter. a warmer car is a more efficent car

Berg · 08-08-2010, 03:34 PM

What would you guys suggest in my 2010 Altima 3.5 v6? Its says designed to run off of 87.Are there many other 270 horse power motors that use 87??

tumnasgt · 08-08-2010, 06:01 PM

If the engine is designed for 87, you'll almost definitely see zero benefit from using 91. On the other hand, there's no harm in trying higher grade fuel (other than too your bank account).

ShadeTreeMech · 08-08-2010, 06:12 PM

My Maxima prefers 91 as well, but after replacing the knock sensor I can run 87 alright.

If the car mfg says to run 87, run 87. It's the most bang for your buck (no pun intended) since 87 combusts at a lower temperature than higher octane. In elevations above 5000 feet, you replace the 87 octane with 85 to get the same results.

With the Infiniti, I suspect the combination of a heavy load with incorrect fuel and higher temps caused the engine to have a helluva time retarding the ignition enough to compensate for the lower octane, resulting in the car retarding ignition way too much to get the necessary power. Good thing you didn't burn a hole in a piston, which has been known to happen with bad enough octane knock.

mcrews · 08-08-2010, 06:56 PM

shadetree,
no kidding....accept I never head a pinging.
talldud,
yeah, I just need to pay attention when I do a trip.

I really drive like an ol'man (no offense to you guys over 54!). Mainly because I LOVE getting great mpg!!! What's nice though is I got plenty of hp if I get in a bind.

your right about what the manufacturer reccomends. they design the optimal performance for the octane listed.

usergone · 08-20-2010, 08:55 PM

I find that my truck (TBI 4 banger) runs smoother and has a much more noticeable power band on premium. It also seems to like my hotter thermostat.

With both of those, my highway driving is much easier (with the better power band)

ShadeTreeMech · 08-23-2010, 10:16 AM

Quote:

Originally Posted by mcrews

shadetree,
no kidding....accept I never head a pinging.
talldud,
yeah, I just need to pay attention when I do a trip.

your right about what the manufacturer reccomends. they design the optimal performance for the octane listed.

Problem with a luxury auto is that engine noise in the cabin is generally frowned on, meaning you could have a rod going out and not know it. Even in my Max it took supreme concentration to hear the pinging, and it was my wife who heard it best! I could barely make it out.

But on a lower class of vehicle, it's REAL easy!

winkosmosis · 09-11-2010, 03:39 AM

Your engine is MADE for 91/93 octane. By running a lower octane you may not notice a difference but the engine does. It's igniting the fuel earlier to prevent it from pinging, which saps energy because the piston is fighting the burn for longer than it should.

There is a reason the manual says to use 91. If you're so poor you can't afford the extra 20 cents per gallon, you need to sell your Infiniti and buy another car! I suspect you're just being cheap without considering the cost of the wear on the engine.

mcrews · 09-14-2010, 01:45 AM

hey winkochickenshxx.....
since your rude name-calling post already already made it to my email, it's only fair that everyone gets to see what you posted then edited

"Dude, I don't think you get it. Your engine is MADE for 91/93 octane. By running a lower octane you may not notice a difference but the engine does. It's igniting the fuel earlier to prevent it from pinging, which saps energy because the piston is fighting the burn for longer than it should.

There is a reason the manual says to use 91. If you're so poor you can't afford the extra 20 cents per gallon, you need to sell your Infiniti and buy another car.

***************

And you need to pull your head out of your axx. You must be trolling looking for old posts that you can strut your "high and mighty better than anyone else" attitude.

'so poor'!!!!!!!!!!!!! who the fuxx are you to make that comment????
I'll tell you.....YOU ARE A SPINLESS WUSS. DOn't even have the courage of your convictions. Make a post and change it 8 minutes later.

I'll tell you the same thing I told the idiot from new zealand who had a problem with me driving an Infiniti.
I'll do what ever the hexx I want. I don't run 87 octane be`cause I'm cheap.....I run it because I can.