Premium gas for a 100

[AndrewP]

It's all about knock.

If you run low octane gas, it's more likely to ping (or spark knock). If the engine senses that via the knock sensors(which it will before you hear it), it retards the timing. That reduces performance and mileage. These trucks get such poor mileage anyway, it's probably hard to notice any difference.

The higher your elevation, the less important the high octane is. So at 5000 feet, I'm sure regular octane gas would be fine.

I think this was a concern only for the early 100s, because I have a friend who had a 98 that called for premium and a 2003 that does not. They must be tuned differently.

There is a slight (very, very slight) BTU advantage to regular gas, and thus the theoretical claims of better economy with regular, but it is also true that lower octane gas is more prone to pre-detonation and spark knock because it actually burns faster during ignition in the cylinder.

 

[rusty_tlc]

I switched to regular after the first year I owned my truck. No noticeable difference in mileage or performance in driving conditions varying from Death Valley to the High Sierras. Over the course of a few years I would say the cost savings has been considerable.

On the question about the age of the truck. Higher octane gas contains combustion inhibitors that prevent pre-ignition of the fuel (pinging) in high compression engines. As the engine ages compression goes down so logically pre-ignition would be less of a problem. ie running higher octane fuel is less important as the number of miles on the engine increase.

It seems kind of counter intuitive that higher octane fuel is less volatile than lower octane doesn't it?

 

[Pskhaat]

I've owned both a 99 and an 04. There was a switch 02-03 (?) where the ECU was mapped to handle low-test better and prior models had an assumption on high-test fuel.

In both Hundy vehicles of mine (and we do a few more miles every year than even you most standard portal user and likely a few even more than your standard 'mud person) I consistently receive better mileage on high-test non-ethanol when heavily-laden and higher-temperatures. As such, the $/mile works out better on high-test, for us.

Our vehicles are mostly used at GVWR for over at least 4k miles at a time, mixed highway and off-highway.

I've noticed better mileage with high-test even at altitude, though logic says it should matter less and less every foot we go up. Some folks think the high-test has a higher boiling point which is quite the issue in the LC80.

 

[ShottsCruisers]

It's obvious to me that the 100 changes ignition timing when running the different octanes.

With regular my truck shifts down on small hills where with premium it does not. It's slower off the line on 87. It does this so it will not knock. I do not know of any 100's that have experienced knocking.

I can tell when I run premium for sure. My mileage is also better by an MPG when running 91. Less downshifting, etc.

 

[Pskhaat]

Shotts, can it be we agree on something?

 

[Brock63]

everything says PREMIUM but just like in my FJC....that is for optimal performance.

I live in Charleston and over the last week or so of extremely high temps I ran a tank of midgrade....good mileage, no pinging even when accelerating on interstate with air conditioner cranked to cool down the 98* external temps.

when everything is mixed with ethanol...i dont see much difference other than price to be truthful around town. On trips or when I need better performance....I found that a non-Ethanol blend works best actually. I got my best mileage running Shell non-ethanol 93 or 97 Octane...cant remember which it was...but was highest and had sticker that said Ethanol Free.

Other than that time...Midgrade Sunoco runs great in my LX....will try a Midgrade and Regular mix from same station one week and let you know...but no pinging and no issues and still got around 13mpg around town during week with AC cranking is not too bad.

 

[AndrewP]

everything says PREMIUM but just like in my FJC....that is for optimal performance.

I live in Charleston and over the last week or so of extremely high temps I ran a tank of midgrade....good mileage, no pinging even when accelerating on interstate with air conditioner cranked to cool down the 98* external temps.

when everything is mixed with ethanol...i dont see much difference other than price to be truthful around town. On trips or when I need better performance....I found that a non-Ethanol blend works best actually. I got my best mileage running Shell non-ethanol 93 or 97 Octane...cant remember which it was...but was highest and had sticker that said Ethanol Free.

Other than that time...Midgrade Sunoco runs great in my LX....will try a Midgrade and Regular mix from same station one week and let you know...but no pinging and no issues and still got around 13mpg around town during week with AC cranking is not too bad.

Ethanol is kind of a paradox.

It significantly raises octane on the cheap.

It also has significantly LESS energy per unit volume than gasoline.

It would make sense to me that the very best fuel economy in an early 100, would be Premium Ethanol Free gasoline. Whether it would be cheaper to operate is hard to say.

One last thing about pinging. In a modern fuel injection/ignition system, you should virtually never hear pinging. The knock sensors are far more sensitive and quicker reacting than your ears, and will retard the timing and eliminate the spark knock, before you even detect and think about it.

 

[ShottsCruisers]

Shotts, can it be we agree on something?

You prefer 80's too? :sombrero:

 

[Pskhaat]

You prefer 80's too?

Yep, I miss hexachromatic artwork I used to hang in the garage:

 

[Cackalak Han]

Man, you're talking about .20 more cents a gallon! That's $2.00 for every 10 gallons you buy. Is that really a huge concern for you? If the motor was designed to be run on 91, do it. Call me crazy, but if you can't afford to run premium in your LC, you shouldn't have bought it.

Depending on how much you drive, that's still a $300-600 per year. That's a mod or two! :sombrero:

Our '04 Sequoia has the 4.7 iforce engine (the same as your LC?) and I have never run anything but 87 octane. It lives at sea level, but has pulled our 6000lb travel trailer up to 9000ft on regular unleaded. It has around 72k on it right now.

I'm pretty sure that the only adjustment that the ECU would make is to advance the timing if more octane were available to do so safely. This might increase torque slightly, which could affect MPG reported by others.

I wonder if the Sequoia/Tundra ECU's are different than LC's? I noticed on my friend's Tundra, it calls for regular, yet both have the same 4.7L engines.

Anyway, been using 87 with no problems. 4,500-5,000 ft.

EDIT: I'm actually using 85, not 87.

 

[ShottsCruisers]

I wonder if the Sequoia/Tundra ECU's are different than LC's? I noticed on my friend's Tundra, it calls for regular, yet both have the same 4.7L engines.

Anyway, been using 87 with no problems. 4,500-5,000 ft.

In '01 the LC had 5 less HP and 5 more in torque due to CPU programming. Maybe for the weight of the LC.

 

[Elijah]

I've now documented 3 full fill ups from the same pump # and same Conoco station. This gas station has no ethanol in their premium grade. It made a big difference in my fuel economy, '99 100 series all armored up. I'd say 60/40 hwy to city driving, first tank was 16.4 mpg, second was 17.1 mpg, and third was 16.8 mpg. The gas was 20 cents more a gallon than the regular. The mpg on the regular fuel was usually right around 14 and that was Chevron regular. So doing the math I come out on top by using the premium from this station. I feel the true difference comes from the fact that there is no ethanol in it. My two metros also saw large increases in the mpg from using the non-ethanol gasoline. The 99 Metro, 3 cyl/manual, saw almost 6 mpg increase over 4 tanks with it, now at 43 mpg running AC all the time. The 92 XFI Metro is at 57 mpg with this gas, 52 with ethanol added gas, no A/C in the XFI models. So I am a firm believer in the no ethanol added gasoline, if you can find it.

 

[CSG]

Right. It's the ethanol not premium grade gas. Ethanol is much less efficient fuel and MPG suffers on any vehicle that runs it. Meanwhile, unless the owners manual calls for premium, I think it's a waste of money.

 

[Pskhaat]

Just a point of reference, and I didn't believe the computer and kept watching the fuel level gauge, until I filled-up and did the maths.

Following a moderately-slow straight truck to Moab, we achieved 24.1mpg on premium fuel at speeds of 55mph (35-40mph up the hills) from Phoenix to Moab in a single tank with a bit to spare. TOTALLY off the charts on mileage, but true. The Chevron in Phoenix must not have had an ethanol mix on the last delivery and Cruisers were always meant to go no faster than 55.

YMMV.

 

[1loudLX]

Just a point of reference, and I didn't believe the computer and kept watching the fuel level gauge, until I filled-up and did the maths.

Following a moderately-slow straight truck to Moab, we achieved 24.1mpg on premium fuel at speeds of 55mph (35-40mph up the hills) from Phoenix to Moab in a single tank with a bit to spare. TOTALLY off the charts on mileage, but true. The Chevron in Phoenix must not have had an ethanol mix on the last delivery and Cruisers were always meant to go no faster than 55.

YMMV.

I couldnt do that, I'd go insane.