I am something of a skeptic.  It takes math, numbers and logic to convince me of the facts.

Here is the setup.  

1988 Honda CRX Si is my day to day vehicle.  I drive 60 miles round trip each day.  

My gas mileage was once in the 38-42 range, but had been declining for the last year or so.  28-31 became the norm.  The car seemed to be driving the same, good HP, good engine sounds, not smoking oil, etc.

On a whim I picked up a white bottle of fuel injector cleaner and put premium gas into the tank.  

I calculated my MPG for the tank prior to filling with premium and 1/3rd of a bottle of injector cleaner.  31 mpg  (has been measured as low as 28 recently)

The extra fuel and cleaner added 11% to my fuel costs.  

After the first tank, I measured my mpg moved up to 34.  (9.6% increase in efficiency  21% better than 28 mpg)

After the second tank, my mpg had increased to 36.  (16.1% increase in efficiency 28%+ better than 28 mpg)

I have always thought that the 'fuel injector cleaners' and running premium gas were a waste of money.  After running the numbers it looks like a no-brainer to pay 11% more for gas to receive a 16% to 28% increase in efficiency.

TheRedGoat


PS.  My point?  Hey this is the GD forum afterall, right?

I picked up a '92 F150 4x4 with high miles late last year... 6 cylinder, 5 speed tranny.  Mileage was 11-13 MPG... Been using injector cleaner and premium fuel every tankful, now mucho more power and mileage has increased to 19-20 MPG.  If you want it to work right, you've gotta feed it right...

My engine was running a little rough, and my mechanic told me to put about a half gallon of diesel in my truck.  He said that the carb cleaners are mostly just distilled spirits and diesel would work just as well.  I was skeptical, but gave it a try.  I put in $1 worth of diesel before I filled up with gas.  

I didn't notice any change until the next fillup, but sure enough it worked.  It had a bit more power and idles much better.  I would not have tried it on my new car, but my rig is a beater (my daily driver).  This reminds me it is time for another half gallon.

I certainly am a convert to this school of thought.  I am going to try the same experiment with my other vehicles.

Seriously, the car seems 'relaxed' now when I am driving down the highway.  Power seems to be smoother, and more rapidly applied.

TheRedGoat

I was told the same thing by an automechanics instructor.  

Supposedly the diesel causes the engine to run hotter, thereby burning off residue.  Not sure if this is true or not.  

The injector cleaner was 1.99, each use cost me 70 cents.  

If the diesel really works just as well, then I will try it next time.

The reason this works is because federal law requires certain additives to be placed in the fuel . Well after time these additives form a layer of varnish like substance on the surfaces of your fuel system . Injector cleaners just remove this layer . SO you can thank the feds for the problem ... of course .

Could be you're unconsciously being a bit easier on the throttle...

At any rate, running the thing at topspeed or close to it for a couple or ten miles will probably do the same.

Government planned obsolescence... if we could actually keep a vehicle running decent for 2 years after we've paid the silly thing off the economy would tank... normally by year three it's entering the realm of 'rolling junk' due to 'engineering refinements'...

If only vehicles were as well built and engineered as the typical firearm...

Atleast I can keep those old F150's running... once the EPA influence disappears...

(ssssshhhhh... don't tell... [;)])

I doubt that I am easing off the throttle.  Most days my commute includes sustained speeds of 85-90.  On others, when the traffic is right, 105 is common.  No kidding.

This little car gets better mileage at higher speeds.  

Use the stuff with the first tank full or two after every other oil change. This will keep the deposits from forming, and keep the engine running as efficiently as possible. Running mid or high-grade gas rather then low will help too. Don't underestimate a tune up if it has been a while.

I have an 85BMW 325e 6cyl, just turned 175k miles on Sat. I run premium(93) in it, once in a while I treat it to Sunoco 94.

I still follow maintenance strictly plus plugs and fuel filter every 10K Air filter every other oil change (6K miles).  I put about 20K on it a year.

I average 25MPG mixed city/hwy.  My bi-weekly 140 mile trip, I usually cruise between 75 and 85 MPH I get 31MPG.  I do not baby the car when it comes to driving.

The car weighs 3900LBS empty

I'm still waiting for the "plug" on which brand of cleaner was used.

I noticed that most fast lube type oil change places offer a fuel injection cleaner.  It costs from $20 - $50 depending on the place.  My wife fell for this and spent around $45 for a fuel injection cleaner to be added to her gas tank.  

I questioned her about it after she came home and said she got the oil changed and fuel injectors cleaned.  I asked her about the type of bottle they put in the tank....YUP, STP fuel injection cleaner just like is sitting in my garage that I paid about $2 for per bottle.

Just thought I would pass this on.

I usually try to run a bottle of injection cleaner through the engine after every third oil change or 9000 miles.

I don't know if it helps, but I like to think it does.

medcop

I run my Ford Explorer on JP-7 jet fuel with Tri-ethyl borane (TEB) injection on startup and when switching to afterburners.  I only get about 10 gallons to the mile, but the sonofabitch will do Mach 2.5.  [;)]

Every 6 months, I run a bottle of Chevron's "Techron" thru my 4Runner.

Jay
[img]http://www.commspeed.net/jmurray/images/iroc-cop.gif[/img]

Fuel octane requirements are generally (but not always) dependent upon engine design (static compression ratio) and mileage (to a limited extent.)

Knock = Detonation = Pre-ignition of fuel caused by heat when compressed.  Higher octane fuels are actually MORE resistant to ignition, and therefore can be run in higher compression engines.  

As mileage increases, both "varnish" deposits (courtesy EPA) and carbon deposits (again coutesy EPA - caused by the EGR system!) build up on static surfaces on the combustion chamber, piston head, and valve heads, and will actually drive up your compression ratio by degrees.  For many engines, this can be enough to push fuel octane requirements up to the next level - akin to being pushed up into a higher tax bracket.

Most truck engines - like my Jeep Cherokee 4.0 - are relatively low compression.  With my 8.8:1 compresison ratio, I can even run Kalifornia's RFG in 87 octane (which actually comes out around 84.5 octane when you are all done figuring!) and still see 21/24mpg.  I still have plenty of power as well - AND 213K miles on the clock.

A quick and easy way to get rid of deposits?  Hold the throttle for a high idle (1500-1750rpm) and use a mist spray bottle full of clean water.  Spray into the intake horn.  The water soaks into the deposits before the spark hits, and then gets flashed into steam.  This serves to loosen chamber deposits without the use of solvents and will cause no harm to your engine.  

Also bear in mind that anything you do to loosen deposits (including commercial cleaners) will send them downstream.  What is downstream?  That's right - the catalytic converter.  It is a fine ceramic matrix coated with an alloy of Platinum, Palladium, and Rhodium that will catalyse the final combustion of HC and CO when heated.  HC and CO are byproducts of the incomplete combustion of standard hydrocarbon compounds - such as octane (the principal hydrocarbon in gasoline.  Cetane is the principal component of Diesel.)  

Why, you ask is the combustion process incomplete?  In a properly tuned engine, it wouldn't be.  By removing most emissions control devices, an engine can be properly tuned.  However, the introduction of the Exhaust Gas Recirculation system - which bleeds a metered amount of exhaust gas (crud and all!) into the intake system - was intended to reduce combustion chamber temperatures.  A water fogger works better.  Anyhow, when you reduce the temperature of combustion, you reduce the EFFICIENCY of combustion, and hamper the process.  Thus, HC and CO emissions go up.  Why EGR?  To reduce Oxides of Nitrogen (NOx,) a princopal component of Acid Rain.

(continued)

NOx is a semi-known problem to old-time street racers - as a byproduct of too-high combustion temperatures.  Many old street rigs had Pyrometer ports in the exhaust manifolds, which allowed a tuner to gage how well the engine was burning fuel.  Exhaust Gas Temperature (EGT) was expected to fall within a specified range - too cold, and you weren't burning all the fuel, too hot, and you were risking detonation and possible engine damage.  Too cold is easy to remedy - lean the mix  touch (this is in the days of carburettors) and maybe go to a slightly "hotter" plug.  Too hot was a little more work.

Too hot required the addition of a "water fogger" system, which introduced a fine mist of clena water into the intake stack.  This mist would absorb excess combustio heat when it flash-boiled, and would (as a side effect) help keep deposits down and enging internals clean.  Too bad it's illegal now...  Only combustion byproduct of water fogs is steam - and that's water that is just reintroduced into the planet's water cycle.  Only trace amounts of steam were released.

In effect, the Catalytic Converter, EGR system, and most of the "Feedback Control System" that centers around the Exhaust Gas Oxygen Sensor could be realistically removed and replaced with existing systems that actually are a great deal simpler and work better.  And, if the various "impurities" in our fuel were to be removed (most of these are byproducts that are put into fuel instead of disposed!) we could have far cleaner engines - and air! - than we currently have.  All with 1950's technology...

Ain't technology wonderful?  All I'd want to keep would be basic fuel injection (no problems on hills with it!) and basic electronic ignition (no points to muck with.)  They can keep the rest of this BS - it ain't strictly necessary...

FFZ

RedGoat, I don't mean to put you to shame, but I get 55-65mpg regardless of fuel grade... hehehe

Doubtful.  The simple fact is, wind resistance gets exponentially higher the faster you go.  Your car WILL burn more gas holding 85-90 than it will at 65.  It's physics man, and Honda hasn't found a way to defeat it yet.  (my car is a Honda... and they're getting closer!)

Ahhh, but the internal combustion engine only approaches maximum efficiency when it is producing its maximum horsepower.  

I left Galveston around 7pm one evening.  110-115mph and was being passed by other traffic.  I get nervous around 125 so I did not pursue them.

I stayed with semi-fast traffic 90+ until Huntsville.

I topped off in Huntsville since I was certain I  would need to replace what I had just wasted at high speed.  The car only took about 2-3 gallons of replacement fuel.  Average mpg for the run was 45, average speed was 92.

FWIW, M1QJ, the high speed run probably just burned out the deposits and that is why I got the higher mileage.  But, hey, it gives me an excuse to drive like a madman, right?  

Aimless, FreeFireZone, thank you both for the detailed response.  

Since my car never knocked or pinged, does this mean the added fuel economy is the result of cleaning the deposits, and not the result of higher octane fuel?

TheRedGoat

Not quite true, as far as fuel efficiency, my car gets the best when the engine is at about 2000-2500rpm, but the engine has the most power around 5000rpm.   You get the best efficiency when your engine doesn't have to do a lot of work to keep the car moving.  Running at peak power, means your car is working harder to keep it's speed, thus burns more fuel.  The only things that reduce that at high speeds are aerodynamic efficiency, and mass (momentum)

The difference in your car between hauling tail like you do, and driving a bit slower will be less noticible in your car, but it will be more fuel efficient at lower speeds.  In my car, if I drive conservatively for the distances you mentioned, I could average 65-70mpg pretty easily, but if I hauled a$$ like you do, it would probably be more like 50mpg  (25-30mpg difference!!)  

M@

Certain gas additives (like MTBE) are mandated to reduce emissions in older carbureted cars. Fuel injection is pretty efficient so these additives do not improve emissions in injected cars. The additives do not have the "energy density" of straight gasoline. In other words, you get lousy mileage (up to 15% less) due to the additives. It's a win-win for the gas companies though. They charge more for gas with additives and you have to buy more gas because the mileage sucks.

Most internal combustion engines have at least four cylinders and pistons. There is always at least one cylinder going through the power stroke and it can carry the other cylinders through the non-power strokes. The maximum efficiency of such an engine is [b]e[/b]max = ([b]T[/b]ignition – [b]T[/b]air) / [b]T[/b]ignition where [b]T[/b]ignition is the temperature of the fuel-air mixture after ignition. [i]To maximize the fuel efficiency, you have to create the hottest possible fuel air mixture after ignition.[/i] The highest efficiency that has been achieved is approximately 50% of emax.

Don't argue with a search engine, buddy.  [;)]

TheRedGoat

M1QJ, what part of Texas are you in?  If you ever get out toward East Texas, look me up.  You sound like you would be fun to toss back a few with, and I happen to know a place in my backyard we could do it.

The efficiency of the engine you're relating to is true, but it's in and of the context of the engine alone, not in the context of moving a vehicle.  Slap your engine up on a block and run it like that, and you'll get decent efficiency.
However, in a vehicle you'll get the most efficiency when the whole vehicle has the least resistance to movement.  This will be when friction from the road and wind resistance.  It's physics man, don't argue with Newton!  [;)]

I'm down in Round Rock (Austin). I been meanin to ask ya about hog hunting.  My buddy here at work has some land and consequently, some hogs, down near Columbus/Sealy.  I intend to use my M1 for hog hunting, but don't have it yet, so I will probably be using my AR for hog work until then.  Mine is a 20" A2, and I've got some South African 55gr fmj surplus stuff.  Think this will work OK for hogs?  Any tips for shot placement?

M@

Carefull there Goat. A few more bottles of that stuff and you'll be having to pull over every once in a while to siphon off the excess gasoline.