Anything bad about Unleaded Plus?

[|97BlaZeR|]

Today I needed gas and the gas station I stopped at didn't have unleaded regular like I usually pump. I put about $15 of unleaded plus in.. will this affect my engine in any negative way?

[RK4332]

It wont effect your engine, but it sure hurts the wallet.

[|97BlaZeR|]

haha yeah i know, it was $3.29 here today, but i was at an 8th of a tank and the next gas station was a ways away.

[BlazerBoyLT98]

Higher octane won't hurt anything, you will get a little less gas mileage I assume ebcause the higher the octane usually the more cleaning agents are added so there is less actualy combustable fuel.

[old_master]

The higher the octane rating, the less volatile the fuel is. High octane fuel takes longer to burn and as a result, ignition timing must be advanced more to efficiently burn it. If an engine spark knocks, pings, detonates, what ever you want to call it, it means the fuel is done burning before the piston reaches top dead center, (TDC) on the compression stroke. The sound you hear is the piston “fighting” it’s way up to TDC. When the engine makes this sound, either the octane rating is too low, or the ignition timing is too far advanced. If an engine continues to spark knock, it will eventually burn a hole in the top of the piston. OBDII equipped vehicles, such as yours, have a knock sensor. When the sensor detects spark knock, the PCM retards ignition timing to reduce or prevent spark knock. Ignition timing is not user adjustable on OBDII vehicles, therefore using higher octane fuel will not help it, but it won’t hurt it either.

[1996LTOwner]

Good info O-M, thanks. My '96 Blazer did not get along well with the low octane. I'd heard that the 4.3 could be particular at times and saw that when I used the 87 octane. Other people I knew said their's ran fine with it but I had to use 89.

[Chris Stewart]

I use 89 octane in my gassers for the improved additive package as I was told many years ago...which I trust is correct, but I guess I could be getting beat.

[sickcallawayc12]

I just can't believe places are literally RUNNING OUT of regular gas. Glad i use midgrade stuff. Seriously when's the last time anyone saw this? (first time i've seen it).

[ericn1300]

Originally Posted by sickcallawayc12

I just can't believe places are literally RUNNING OUT of regular gas. Glad i use midgrade stuff. Seriously when's the last time anyone saw this? (first time i've seen it).

it's probably all the people who used to by a higher grade dropping down to save some bucks.

[Great_Auk]

Have a 95 S-10 Blazer, 4X4, 4-door SE
Has the 4.3L V6 HO engine.
Have been only using 91-92 octane gasoline.
Am getting 20-21 mpg on the highway.
And 16-18 in town.

Just got back from a 165 mile trip, and got 23.5 mpg on all
highway driving (both 65 & 55 mph roads)

Is this unusual for this engine & vehicle?

Has had a "full tune-up" about 3 months ago,
right after I bought it.

Am using Mobil 1 5W-30 synthetic oil.
And new tires.

[ZL1power69]

thats slighly above average economy for 4x4 s-series trucks but using premium fuel is only hurting your wallet and doesn't increase economy. the pcm is programmed for regular 87 octane fuel from the factory.

[Sparky1349]

Originally Posted by old_master

The higher the octane rating, the less volatile the fuel is. High octane fuel takes longer to burn and as a result, ignition timing must be advanced more to efficiently burn it. If an engine spark knocks, pings, detonates, what ever you want to call it, it means the fuel is done burning before the piston reaches top dead center, (TDC) on the compression stroke. The sound you hear is the piston “fighting” it’s way up to TDC. When the engine makes this sound, either the octane rating is too low, or the ignition timing is too far advanced. If an engine continues to spark knock, it will eventually burn a hole in the top of the piston. OBDII equipped vehicles, such as yours, have a knock sensor. When the sensor detects spark knock, the PCM retards ignition timing to reduce or prevent spark knock. Ignition timing is not user adjustable on OBDII vehicles, therefore using higher octane fuel will not help it, but it won’t hurt it either.

Hey Old Master, I have seen your posts regularly in this forum and agree with many of the things you have written so I have respect for your opinions. I would like to comment on a couple of items in this particular post though. Volatility is the measure of how easily liquid fuel changes to vapor fuel (i.e. vapor pressure), it has nothing to do with octane, av-gas is high octane and high volitility so at high altitudes (low temp, low pressure) gas will still vaporize. Premium gas sold in Pheonix is high octane (well sort of) and lower volitility especially in the summer so that the gas will not boil in the gas tanks parked on black top in the sun. Refineries very the volitility from region to region and season to season. In the summer you want a little lower volotility to prevent excess vaporization (and overloading evaporitive emission charcoal canisters) and vapor lock on cars with mechanical pumps mounting on the engine in the old days. In the winter you want a little high volitility to improve cold starting (if you have ever driven from Pheonix to Flagstaff and seen a 50-60 degree temp change w/Pheonix gas in your tank you'll know what I mean, not as big a problem now as it was with carburatored cars).

Octane is a rating of the anti-knock index of a fuel, fuels with otherwise identical characteristics with different octanes will combust (i.e. burn) in the same period of time in identical engine characteristic. The anti-knock index is the ability of the fuel to prevent knocking (detonation) which is the fuels tendency to combust due to heat and pressure as opposed to due to a spark and the resulting flame front. During normal combustion the spark plug ignites the fuel and the flame front traverses the combustion chamber gradually, think of a grass fire in a field. The edge of the grass starts on fire and the flame burn across the field roughly in a line, same thing in a combustion chamber. During detonation as the flame front move across the combustion chamber the remaining unburned fuel mixture is heated and compressed, if the heat and pressure exceed the fuels ability to prevent detonation then all of the mixture burns at once rapidly raising the heat and pressure in the combustion chamber (think of the field with the grass fire, the whole remaining field of grass instantanously lights at once). This rapid rise in pressure actually causes the engine block to vibrate, this is the sound that can be heard during detonation (and why knock sensors are usually screwed into the engine block). Detonation can occure prior to the piston reaching TDC or while the piston is dwelling at TDC during the time known as the constant volume combustion period (the few degrees before, during and after TDC when the crank is moving but the piston is not). Detonation can happen after TDC but this is not as common. While causes for detonation include low octane fuel and excess timing advance other factors can cause detonation including excess combustion chamber deposits and lean fuel mixtures (which increase combustion temperatures).

Vehicles with knock sensors may or may not benefit from using higher grade (octane) fuels. If your engine does knock on 87 octane and the PCM retards your timing you will most likely not know it, the effect of the retarded timing is poorer performance and lower fuel economy. By putting higher octane fuel in you may improve performance and economy, HOWEVER unless your vehicle is specifically designed for premium fuel (because of higher compression ratios) you will never notice the change in performance and economy since most vehicles are designed to run on 87 octane gas. In the event that your PCM is retarding the timing it is so slight that even a professional driver wouldn't notice the difference. In an article I read recently on Yahoo finance concerning saving money on fuel it said that 80-90 percent of the people putting mid and high grade fuels in there cars were not getting any improvement in performance or economy. In another article I read in Yahoo Finance a couple of years ago it was stated that retail gasoline suppliers were cheapening up there lower grade fuel by skimping on additives like detergents and anti-injector fouling agents, although they haven't removed them from higher grades it still isn't worth buying the higher grade gas just to get the better detergents and additives. The article recommend every 5-10 tanks to put a bottle of fuel system additive in, at a few dollars at the autoparts store you are way ahead of putting $2-$3 of higher priced gas in every tank.

Don't know if anyone is actually going to read this far down, but I gotta ask this - Has anybody noticed in the Shell gas ads about preventing the build up of gunk in your engine that when they show the Shell gas valve that they are showing you an INTAKE valve and when they show you the cheap gas gunky valve that it is an EXHAUST valve?

Sorry for the length, hope this info is helpful in deciding which gas is right for you.

Sparky.

[old_master]

WOW! Nice post! I tried to keep it short and sweet but you did a great job on the details and technical end of it. The GM Vortech, Chrysler Hemi, Ford HSC, and the Honda CVCC engines all mix the air and fuel mixture more thoroughly than the conventional combustion chamber design. The hemispherical combustion chamber configuration on each of those engines provides a more uniform, predictable, and thorough burn. So the next time someone asks about your Blazer you can say, "Yeah, it's got a hemi".

And yes, I did notice the switcherooo on the valves. Not too many people know how to tell the difference between intake and exhaust valves, even when they're next to each other.

[Great_Auk]

Interesting information in here.

When I use 87 - 89 octane fuel, my milage gets worse.
So I guess my timing on the engine is set for premium.
My owner's manual says that under light load conditions,
I can use 87 octane. (I seldom drive under light load conditions.)
Thus, I use 91 octane or higher. (Page 6-2 of 1995 Owner's Manual.)
As I am usually hauling people & gear around, I have been using
91-92 octane and getting 20-21 mpg on the highway. (3-4 people
and gear in the Blazer.)

I do get a "bad" tank of gasoline, once in awhile (idles with a
"clunka, clunka, clunka, and has poor accceleration). Then I just get
a bottle of gasoline additive in the tank, and drive it out.

The 6.3L has enough 'power' for my needs. I have a trailer, but no
hitch on the Blazer. So have not tried to pull anything, yet.

Have been very satisfied so far, when the Blazer is "healthy".
Need the 4-wheel for Wisconsin winters (and summer potholes).
One of the people I drive for lives on a very remote, township
dirt road. Has been ok in dry weather, but a mess after a large
rainstorm, or any amount of snow. (Last serviced.)

Saw that Shell commercial. And almost got a driving job with them at one time, years ago. NOT a gas truck driver, either.
Most TV ads are 'barely' legal.

Will keep an attentive eye on these forums.

[Blue Bowtie]

So the next time someone asks about your Blazer you can say, "Yeah, it's got a hemi".

Wow. What a degrading, revolting statement. Personally, I would endeavor to avoid EVER classifying it as such, and for multiple reasons. At best, it's a "semi-hemi" since the chamber is not of the traditional full hemispherical design (thank God for that!).

FWIW, the true "hemi" is not really an advantageous design, but a marketing ploy. "Hemis" have been getting their asses handed to them by equal displacement wedge- and semi-hemispherical combustion chamber engines for decades. Even in the early '60s, the Ford 427s were sucking in, chewing up, and spitting "Hemis" out the exhaust valves routinely with a whopping 1 inch more of displacement. That'll probably start a heated discussion, but quantitative results speak louder than any amount of subjective perception and whimsical theory. Some car buying people are just slower to learn the difference between toothless advertising hype and well-engineered reality.

Hemi? Oooooh... That just makes my skin crawl. Might as well stock up on a bunch of Carter AFBs and dual-point distributors, too, since those philosophies go hand-in-hand with those marine engines. Get a box of clear distributor caps while you're at it, too.

Hemi? Yucko! I'm gonna go hurl now...