Any mechanics here?

[jeffmb]

My wife's car says it is required to use premium gas. Premium gas now costs 60 cents more a gallon than regular. :shock: That's $12.00 more a tank. Will it damage an engine by using gasoline of a lower octane than the engine requires?

 

[Jeepnik]

You may experience pinging. This can damage plugs and cause extra stress on the mechanical parts leading to premature failure

 

[Bear Paw Jack]

I would try regular gas and if you get a ping, then I'd finish filling it up with premium. Experiment some, no guarantee regular will cause a ping, but if it does you know what it is and you add what they say. Friend had a car that said the same thing, mechanic said what I said. He was able to use Regular. Lot's of variables, from altitude to you name it.

 

[wizofwas]

Assuming that you have a relatively new car, no it won't hurt it at all. The computers in cars these days are suppose to correct the timing so that you won't get any ping.

 

[pete44ru]

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Regular gas can be used, as long as you use an octane booster/additive with each tankful.

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[gunzo]

Not an answer, responding to a question with a question, which I don't generally like, but trying to be fair or informed, before my answer................ what kind/brand, or model car requires premium or high test fuel?

 

[Colonialgirl]

Jeff;
My Volvo ('98 S-70) specifies Premium gas but since I have no hills to climb and mostly flat driving I buy the mid-grade and get NO PINGS. I have driven up to Contenders place several times on the mid-grade with NO problems. Go mid-grade, lose a mile or two per gallon, but save $0.20- $0.30/gallon. NO NEED for the additives. Coastal SC is pretty flat and you should be okay.

 

[Colonialgirl]

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Regular gas can be used, as long as you use an octane booster/additive with each tankful.

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AT the price for THOSE additives, You might as well buy the higher grade of gasoline.

 

[jeffmb]

Not an answer, responding to a question with a question, which I don't generally like, but trying to be fair or informed, before my answer................ what kind/brand, or model car requires premium or high test fuel?

It is an Infiniti G35. The owner's manual and the gas cap say "premium fuel required". I have read that using octane less than required will damage the engine over time. The difference per gallon around here between 87 and premium is now .60 a gallon.

 

[CGDustDevil]

Assuming that you have a relatively new car, no it won't hurt it at all. The computers in cars these days are suppose to correct the timing so that you won't get any ping.

Wizofwas is right - Modern vehicles will 'adjust' themselves to conditions within reason. My 2004 Tbird 'requires' premium... I put regular in it a few times after break in to see what would happen. My mileage fell off a little for a tankful, then bounced back a bit, although wasn't quite as good as with premium. I DID experience a tad of pinging at times of high loads that the self-calibration feature just couldn't correct for, probably due to our high ambients (thinner air) out here in the desert. (Heavy acceleration, on steep hills etc) I don't typically drive with a lead foot, so I wasn't too worried. I actually do run premium in it as a rule, but I wanted to know what it would do if I couldn't get premium, or couldn't find 'brand name' gasoline under some controlled circumstances.

Premium fuel has a slower rate of combustion, thereby spreading out the explosion (and release of energy across the pistons and heat across the heads) more evenly. Lower octane fuels burn quickly, and can make for 'hot spots' in the heads, bang the pistons around a bit and cause the loss of some horsepower because the combustion cycle will be shorter, and uneven. In the old days of analog ignition with breaker points, we'd retard timing just a tiny bit for engines that misbehaved on regular fuel due to high compression. With better fuel, we could set the timing per spec, or even advance it a couple degrees for a bit more 'snap' without risking any damage to the engine from pre-ignition.

Hence - If you operate your vehicle in more of a 'light duty' fashion, you'll probably be fine with a decent 'brand name' regular fuel. If you anticipate a hard load/severe duty, I'd run a partial tank of premium through the old girl prior to the expected journey in order to give the engine time enough to re-calibrate itself. In very hot ambient temps, I'd recommend the higher octane. (As Pamela suggested, mid range octane, if available, could be plenty good) I'm told that very modern vehicles can react to regular fuel with 'fault codes' occasionally. (Usually on emissions)

Octane boosters can help, but some have side effects! (Environmental nasties, personal health drawbacks, fouling of plugs causing misfires, etc etc) If you're going to use an octane booster, I recommend sticking with products that use MMT (Methylcyclopentadienyl manganese tricarbonyl). It's a product widely used by refineries to regulate their octane, and it's the least offensive of the several types. You might even see the name on your neighborhood filling station gas pump as a 'feature'!

If your fuel has a lot of ethanol, I'd be very careful with octane booster since ethanol itself is a form of octane booster. (Sometimes used in racing engines) You can certainly cause yourself some horsepower and combustion problems by overdoing it! Adding octane booster to say, 91 Octane fuel will probably result in loss of power, loss of mileage and probably some deposits inside.

Good luck!
Regards, Pete

 

[gunzo]

Using premium fuel in this model seems to have helped the car meet emission standards as the primary reason. Not requirements of a performance, tuning, or longevity issue.
Let your wallet be your guide.

 

[Captain America]

That's a high performance car and the higher octane fuel will allow it to perform at it's maximum level. Higher octane gas burns slower and will push the piston further down it's stoke rather than a shorter punch from lower octane fuel. Your ECM may compensate for this by changing timing, adding fuel, or changing the variable cam/valve timing to reduce cylinder pressure which will help the engine deal with the lower octane fuel. Do your due diligence and try different fuels because the lower octane fuel may decrease your fuel economy or the performance of you car so much that you may want to use the premium fuel.

 

[redhawker]

From '04 to '16 I had a Dodge Ram pickup with a 5.7 Hemi engine. It was supposed to use premium. I used regular for the life of the vehicle and never had a problem, never noticed any pinging. When I traded it in it was still running almost perfect (had a small exhaust manifold leak) at about 170,000 miles.

 

[Kevin]

We have had a couple cars which require premium gas. An Audi and my current car a 2015 Lexus. Around here the difference in price isn't $.60 so I just add the premium gas. I'm not a mechanic so I can't say if it's necessary... but is the price difference worth the repair price of any potential engine damage?

 

[Dan in MI]

I'm not going to wade into this one because there are way too many variables being discussed to not degrade this into a peeing contest.

The manufacturers do have a clue as to what they are doing with a high compression engine.

Modern engines can compensate SOME for fuel variations, but there are limits.

A 1980's controller is vastly different than a 2010 controller.

There was a recommendation to use additives with MMT --- DON'T DO THAT. --- MMT plugs catalytic converters. Contrary to what was posted MMT is NOT used in the U.S. anymore. Hasn't been for many years. Canada quit years ago too for the same reason. They did use it much longer than the U.S. Countries that use MMT require different cats than North America. (larger holes in the catalyst brick)

 

[Mega Twin]

Does your owners manual have any guidelines,or substitute info?
I have been in areas where regular unleaded 87 octane was all that was available.

 

[jeffmb]

We have had a couple cars which require premium gas. An Audi and my current car a 2015 Lexus. Around here the difference in price isn't $.60 so I just add the premium gas. I'm not a mechanic so I can't say if it's necessary... but is the price difference worth the repair price of any potential engine damage?

I hear you. I understand that these high compression engines require premium for maximum performance. If that's the case I would have no problem using 87 since the wife doesn't "drive it like you stole it". My concern is any possible long term damage cause by the different burn rate of the fuel. When we first got it, there was only .20 to .30 difference a gallon. Had no problem with that. But .60 a gallon requires a little investigating.

 

[wwb]

If the engine has a sufficiently high compression ratio, it will absolutely require premium fuel to prevent detonation. One thing that was mentioned earlier was the burn rate of premium fuel as opposed to regular gas.... not quite correct; the burn rate is essentially identical. The difference is the ignition temperature.

Diesel engines (referred to as "CI" or "compression ignition" engines) have a very high compression ratio, resulting in a very high temperature at the top of the compression cycle. The fuel is then injected and spontaneously ignites (actually slightly before TDC to allow for combustion time, but this is a minor point). With a "SI" or "spark ignition" engine, the fuel is already present. The fuel/air mixture is compressed, and then ignited by a spark. If the compression ratio is high enough, the temperature in the cylinder will reach the ignition point too early, resulting in spontaneous ignition (detonation or pinging). The higher ignition point of premium fuel will prevent this.

 

[Jimbo357mag]

Amazing what you can learn here.

 

[DGW1949]

The "pinging" one hears is evidence of detonation.
Basically speaking, "detonation" occurs when the air/fuel mixture explodes instead of burns. Regardless of what leads to it happening, the actual culprit is excessive combustion temperature.
The severity of detonation varies, sometimes resulting in a mild pinging sound, sometimes a rattling sound, sometimes much worse...meaning that it may sound like a mechanical knock. On the other hand, if it's mild enough, you may not hear it at all.
Either way though, you can bet that there's some amount of irreversible damage being done to something, somewhere...might be something as minor as premature spark plug failure, or as major as piston ring, valve or head gasket damage. In an extreme cases, I've seen it melt the top edges of pistons and literally break the top piston ring into pieces....
Not saying that simply using the wrong grade of gasoline will cause all of that, or cause any of it in particular...just saying that if your engine is "pinging", it's trying to tell you something, and that if it was me, I'd listen to it.

DGW