Got a question for all of you. I am thinking about buying a used Acura TL, but read that it requires premium fuel and I do not want the added expence.  My question is, what would happen if I were to buy the car and use regular fuel in it instead?  My brother used mid-grade fuel with an older Lexus without any noticable problem.  Any thoughts?  Thanks.

You can safely drive a grade lower than recommended, however do not drive it like you stole it. Detonation accurs under higher loads so if you drive conservatively you will have no problems.

OTOH, using more octane than recommended in your manual is wasted money.

BrenLover

The only problem you would encounter is spark knock during acceleration. This however if bad enough can cause engine damage

in agreement with SO using premium fuel in cars calibrated for regular is pissing away money. Regular fuel has the exact same additive base as premium, the only difference is octane level.

I persnally would stay with the manufacturer's recommendations. In order to save a few bucks, you could end up destroying the engine, which is pretty expensive proposition. Conversely if the manufacturer recommends regular, and you put in premium, you are just plain-out wasting your money by paying for unneeded increased octane rating.

Stay with the manufacturer's recommended fuel grade. You could of course buy 81 octane fuel instead of 91, but in my experience, you'll just use more of the lower grade fuel, so the price per gallon advantage gets eaten up by the decreased gas mileage. So you might as well go for the smoother ride.

MORE POWER

I would either follow the manufacturers recommendation or run a grade lower fuel most of the time and then fill up with high test every couple of weeks. At least that way you are getting rid of the valve varnish, etc that usually goes hand in hand with low octane fuel. I drive a civic and noticed some power loss , and knocking around 90k miles on low octane gas. After I switched to high test, the knocking is gone and I have more power captain!
~ymmv~

BYU,

What type of driving do you do? I have a 99 Crown Vic that calls for 87oct but after driving some 66k of mostly highway mileage casued an increase in varnish and carbon buil-up and would cause knocking under heavy acceleration.

This over time will raise the octaine requirement casueing spark knock during heavy loads or acceleration. If this is your problem going to 89 or higher oct will cost you more than needed.

Buy a bottle of Cleaner that has TECHRON, I cant remember the Brand but it was a well know national brand that is made by one of the major Gas producers and is one of the few that REALLY work. I put a bottlee in a half tank of gas and ran it right down. This lowered my octane requirement to 89. I then ran 2 bottles of it with 3/4 tank and ran it down. I can know use 87oct with no pinging at all under WOT. Total cost of additive was $18 and now I use tankfulls of 87 saving about $3 a tank. Then use 1 bottle every 3000 or so miles.

BrenLover

not always. my firebird had a knock when it drank regular unleaded, but when i use midgrade she purrs right along.

Stick with the manufacturer's recommendation.

Fuels produced today offer excellent varnish protection unless you living Kalifornistan where MTBE is the norm (Fuzzy orange sparkplugs).

Hi-octane means the fuel vapor will not ignite spontaneously at high compression, the heat energy offered is the same, however. Silent Detonation is a killer...most engines that specify high-octane fuel REALLY need it. If if you don't hear your engine knocking, it doesn't mean that it isn't.

Silent detonation is intermittent detonation on one or more cylinders at every second or third combustion cycle, it will usually manifest itself in the hottest running cylinder (Inline 6 cylinder owners, beware) or the cylinder with the highest compression (there are ALWAYS variations). Depending on your engine, you could be beating your engine slowly it to death every time you pull away from a stop sign and never know it unless you hit the accelerator hard enough to hear and feel more cylinders detonate.

While 91+ octane may be recommended, the car must be mfgd to run acceptably well on regular 87 octane fuel.

Modern engines w/electronic engine control units have knock sensors and good knock-avoidance adaptive strategy algorithms to back off ignition advance (and perhaps richen mixture at slightly higher loads & RPMs) - and stay backed-off if knocking persists. Eventually the system 'adapts' to fuel you use and you have no problems.

I used to reverse-engineer EFI/ECU software for a variety of non-US brands. Knock sensors were pretty good - we could even jack the timing up ridiculously and the knock sensor would hammer some sensibility back into the ignition timing curve.  Base tuning curves are conservative, however, in many brands so we could get some extra horsepower by redoing the advance curve and sometimes ever so slightly *leaning* the mixture at given load/RPM points. (Richening mixture often *reduces* horsepower!)

[BTW - I have little experience with Fords, but an ME/racer guy with whom I worked and who was an acknowledged engine control expert, said that from his racing experience, stock Fords are mfgd with a pretty untuned base advance curve that is adaptively put into shape thru a knock sensor + algorithm.  Thus putting 'power chips' into stock Fords doesn't make too much sense until there are major engine changes (intake, headers, exhaust, stroker job, etc.) deserving of a full retuning.]

[BTW#2 - in our estimation, Shell 91 (in Kalifornia) did not seem up to snuff.  For our Dinan turbo BMWs we did some controlled tests w/o knock sensor engaged and we could see earlier knock onset + elevated CHT with Shell than other fuel brands.  Other brands were largely the same and OK, but Chevron came out on top with best knock performance/lower CHT.  While base fuels are supposedly 'fungible' (the same, or exchangable w/no perceptible difference) different additives, detergents, etc. are added by various brands. This prob has something to do with differences.]


Bill Wiese
San Mateo, CA

Hold the phone!

You're buying an Acura, but you don't want the added expense of premium?  Get yourself a Honda Civic then.

Highway driving, pinging going up hills and getting on the freeway. Started filling up with Cheveron Techron gas and it cleared right up. Thanks!

Correct me if I'm wrong, but I'd figure you can get benefit from using higher octane gas.  Most cars, like mine, compensate for knock using timing changes.  When you switch to a higher octane, the engine/controller no longer needs to compensate for knock avoidance.  More power?

M@
(who drives a 2002 Honda Insight)

No problem BYU.

Bweise, you brought up something I had for gotten, good point about retarded timing.

It should also be noted that pre-03 crown vics and Grand Marquis DO NOT have knock sensors to retard timing so how you driving/mods/oct are much more critical. I would assume that other fords also did not have them unitl 03 if the vics did not.

Chevron gas already has TECHRON in it but in a much lower concentration than if you add it. Take a bottle and fill up with mid-grade and go really open her up on some ramps, hills etc. Its good to open them up now and again to help aid in breaking up the carbon.

Bryan

Wow,

> should also be noted that pre-03 crown vics
> and Grand Marquis DO NOT have knock sensors
> to retard timing so how you driving/mods/oct
> are much more critical. I would assume that
> other fords also did not have them unitl 03
> if the vics did not.

...are you sure about that? I'd've guessed that just about every modern car had a knock sensor.
Hell, lotsa cars have multiple knock sensors spaced around the block.

There is indeed an algorithmic method for the ECU to detect knocking (preignition) without a knock sensor. It's called crank-jerk detection: the ECU  monitors engine position and thus velocity/acceleration of crank; knocking will be jerky and at wrong time (a fuel parcel typ takes around 2ms from ignition to combustion; this constant time at varying RPMs/operating conditions is why you have an advance curve; so when a rapid movement is happening to early, system knows it's knockin'.)

So the ECU 'knows' something's wrong and backs off timing (and also occ. richens mixture).

As I recall, this is used for backup if the knock sensor system fails. [Lotsa backup strategies in engine control: for example, mass-air-flow systems can revert to simpler speed-density control if they also have a MAP sensor.]

Bill Wiese
San Mateo, CA

I thought so, too - my '87 K20 had one. It just screwed into the water jacket, and I guess it picked up pressure waves caused by pre-ignition and backed off the timing accordingly.

Ever here of Dyre Straights, If you want to run cool,you got to use some heavy fuel.  

Nuf said      Bob[8D]

If a manufacture says you have to use premium fuel, you better use it. Engine damage is a real possibility. If you got the dough to get an Accura, you gotta kick in more to drive it! Would you shoot pea gravel out of your AR if it were cheap enough?

Techron is made by Chevron, I have used Techron for a long time as part of routine maintenence and have never had any problems with my fuel injection systems.

Then you can't afford the car.

Buy something cheaper.

Bwiese thanks for the post.You know your stuff

I have had a little trouble with build up in a few different makes and model in the injection system and carbon on the intake/valves.
We did some testing and found a product it is made by a company call "B&G" the cleaner is called "44k" it works it contains the same cleaner as the chevron fuel but in a higher percentage.
I never recommends products, but if you suspect carbon/varnish deposits this is a good choice.
I hate to say it but it seems dealers are the only one to stock it in our area.

premium fuel is was the only way they could get it to pass the EPA test.

Hey!

One thing I would like to point out... What the car manual says for octane rating [i]can[/i] be confusing (it caught me).

Most cars (imports especially) print things like this:
[u]But[/u] most pumps state octane as a [i]formula[/i] of the RON & MON.

So look at the pump and see if they state Octane=(RON+MON)/2

So for the given above example recommended octane, the vehicle needs a minimum pump rated octane of 90. (95+85)/2=90. Which is premium at most pumps.

Just thought you would like to know. Because I have seen people wasting money by putting to high of octane in their vehicles.

Oh, and looking at most engine manufactures do say (although hidden) you can run a lower octane, but ONLY if your vehicle doesn't suffer from pinging with the lower octane. If it does ping, put in higher octane. So start low, then work up.

Let see here:

$0.20 - extra charge per gallon for premium fuel
20 gallons a week
52 weeks in a year

=

Wow, you are out a whole $208 a year, and i think thats somewhat conservative. Put the good stuff in it ya cheap bastahd. If it is calling for it, like the other said.

PS - I can't wait for the Ethanol changeover in the PRK. 91 octane and pinging right now! Sux! You would think that all the hippies in this state would love to get rid of cancer causing MTBE and go with all-natural ethanol. Go figure. I guess its the land of fruits and nuts versus the land where car is king.