octane and towing/loading

MajBach

Chief Petty Officer
Joined
Jun 21, 2003
Messages
564
Some of you might find this enlightening while others might consider it common sense. I myself was very surprised when I first learned about it since I had already arrived at a conclusion [erroneous] on the subject. <br />Decades ago when I got my first car, aside from waxing the paint right off of it, I always ran preium gas in it - and it was just a puddle jumping import. I read up on the pros and cons on running high octane gas in engines that didn't require it and then conducted all kinds of 'road tests' (remember I was 17). The first few times I didn't notice any better acceleration times or no increase in fuel economy, I assumed I did the tests wrong. I finally gave in after months - maybe years - and realized you can't make a '79 Accord go any faster or produce more power with additives or good gas. This conclusion was further substantiated when I tried running 130 octane av-gas in my car. (Our float plane bases cached huge tanks of fuel as one cannot get gas readily in the far north). In a vehicle that doesn't call for it, running higher octane gas is like taking vitamins when you already have a balanced diet.<br />So imagine my surprise when I notice a sustantial increase in performance and mileage when I ran high octane for the first time in my car after towing a heavy boat. I thought maybe the air was just dense or that recent car wash did more than clean the exterior. I later learned that high octane gas can greatly improve performance and mileage when used under heavy loads. In the 'old' days, this requirement was indicated by knocking when you put the hammer down or went up a hill. But my last car never did this so I never served hi-octane. Well, not to long ago I learned that most modern cars have anti-knock sensors ( I have heard of these before but never put 2 and 2 together). In other words, if your car starts to knock, the computer lowers the amount of gas it spits in to prevent the knocking or pinging. <br />When towing my boat, my vehicle went from 25 mpg to 29 mpg and there was one particular hill on the way to the dock that ALWAYS req'd me to shift down 2 gears; with the higher octane, only one. I measured this over several trips to be sure too.<br /> So all of you guys in my generation that have concluded that hi-octane gas does nothing for your car if the manual doesn't call for it, guess again. It actually might, give it a try.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,149
Re: octane and towing/loading

I Can't Argue with your Conclusions......<br />Sounds like you Spent an Awful Lot of Money on Gas you Didn't Need.....<br />And Actually it's the Timing that gives you More or Less with a given Octane + Compression......<br />High Octane Gas Doesn't Burn as Easily............ ;)
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,160
Re: octane and towing/loading

Many modern cars use a knock sensor that listens for knock and retards the timing if it hears it, otherwise if you are using gas that is high enough in octane not to knock, you will get the benefit of more ignition advance and better performance. But if you have no knocking, and no knock sensor, using premium is a waste of money. I usually use mid range in my Jeep 4.0 because it pings lightly on regular, and in summer when towing the boat I use premium to avoid any pinging in hot weather.
 

MajBach

Chief Petty Officer
Joined
Jun 21, 2003
Messages
564
Re: octane and towing/loading

I stand corrected, the timing is affected, not the amount of fuel injected.
 

Lark40

Senior Chief Petty Officer
Joined
Oct 29, 2001
Messages
793
Re: octane and towing/loading

Both my 1996 Jeep with the 4.0 six and my 2004 Jeep with the 4.7 V-8 specify that you use regular in normal use and premium when towing.<br /><br />You can hear the pinging quite loud if you forget and start to tow a heavy load.
 
D

DJ

Guest
Re: octane and towing/loading

A little bit of "pinging" in certain conditions (NOT ALL THE TIME) is not harmful. That means your fuel/air mixture is right on the edge. This is what is wanted in a 4-cycle engine. It's called stoichiometry.<br /><br />Actually, running premium in an engine that does not require can turn an engine into an "octane junkie". The reason being is that higher octane fuels burn slower. This opens us up for some of the fuel not burning and leaving deposits. When regular fuel is used again, those deposits may glow and cause pinging and predetonation.
 

Realgun

Commander
Joined
Jul 31, 2003
Messages
2,484
Re: octane and towing/loading

I have a flexfuel Ford Ranger and E-85 has about 100-105 octane. I get better milage when towing with E-85 but when just diving I use regular. I get better milage that way. 10 on Gas and 13 on E-85 towing however the Milage is 15 on E-85 and 20 on regular non towing.
 

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: octane and towing/loading

Realgun, E-85 is a new one to me...what is it???<br />That's not the 85 rated ethanol is it???
 
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