Premium vs. Regular Gasoline

I have been told my a professional mechanical engineer and a well-know car expert (whose radio show is broadcast in Dallas, TX) that the use of PREMIUM GASOLINE is not required even though the manufacturer specifically “requires” it in their owner’s manual. The two individuals who stated that premium gasoline is not recommended are of the opinion that the automobile computer will compensate and adjust for the use of regular in lieu of premium. Do you agree with that analysis?

It’s irresponsible to make blanket statements like that on the air, as other posters will agree! I am an engineer and an SAE member and the answer is not simple!

Some car manuals say that premium is “recommended”. These cars will perform best on premium, but could run on regular without pinging; the computer will compensate, but the engine will produce less useful power.

Others specifically say that premium is “required”. These cars will likely not only have reduced power, but will often “ping” on acceleration, and may eventually ping all the time and burn holes in the pistons.

I am therefore concluding that you may not have heard the whole explanation by the engineers, or you are confusing “recommended” with “required”.

In any case, no responsible engineer, not even in Texas, would make a blanket statement on the air that all “premium” cars can safey run on regular.

I invite other regulars to add their comments.

In most cases, yes, premium is a waste of money…The five octane points that separate “Regular” from “Premium” are not enough to worry about or cause engine damage.

If your engine will not tolerate “Regular”, you will know about it the moment you try to accelerate…

Absolutely not. The so called “professional” is wrong. If the vehicle “requires” premium then you must use premium fuel to keep from damaging your engine. If it’s “recommended” then the “professional” is right. The computer will compensate and all you will have is decreased performance. The professional mechanical engineer knows nothing about the mechanical makeup of engines if he is making that statement. He is doing a disservice to the people of Texas and anyone else who hears his misguided advice. I would like to see him explain away a big hole in the top of a piston from an engine that required premium fuel and was fed regular gasoline.

I think this engineer is incorrect and he’s doing something that is very common; generalizing and using a one size fits all scenario.
Some Premium required cars will run just fine on Regular with zero problems and some won’t; even cars of the same make, model, and with the same engine.

The ECM, or computer, along with knock sensors, EGR system, etc. can control pinging only up to a point. At some point and if it’s bad enough, clattering will occur because the ECM has thrown in the towel and given up.

Have you ever seen an “unleaded fuel only” engine damaged by lack of octane?? I have not. I don’t think such an engine exists.

When these luxury cars are in the hands of their third owners, 160K miles on the meter, they seldom if ever are fed the premium fuel they “require”. They run just fine and without complaint…

I’m a petroleum engineer, and I also disagree with the expert. ‘Required’ means ‘required’. Might the car run without damage? Maybe yes, maybe no. It will certainly deliver less power, and will likely deliver poorer mpgs. I can’t see how all those real and potential downsides are worth $.20-.30/gallon. By the way, which radio show is it?

I humbly submit the following You can’t always count on knock sensors

Use what the owners manual calls for.

Good post!

If you read the article, you will find that octane had little to do with this engine failure…

At some point during travel, between 2000-2500 rpm ? or normal highway cruising speed ? the engine’s management system had adjusted the air fuel mixture to work too lean causing a retarded spark ? but crucially ? it allowed for a simultaneous turbo boost which led to a catastrophic pressure build up in the cylinder chambers.

This caused cylinder six to fail quickly -leaving yours stranded.

Mr. Sutter’s team concluded that the resulting pressure in the chamber was four times greater than the stress during full throttle acceleration.

“We’ve been working on a new calibration which should be implemented in coming days,” he says, indicating that this will ensure proper engine management going forward during what we might describe as “lean times” during the fuel consumption of a given SRX Turbo.

They’re wrong. and highly irresponsible.

If you use regular gas in a vehicle that requires premium you risk preignition. Preignition can come in two forms, pinging or knocking. Both are the sounds of shock waves propogating through the engine from combustion processes happening at teh wrong times. Pinging left unaddressed can burn a hole in a piston. Knocking can destroy and engine much more quickly. Knocking is the sound of the explosion wavefront hitting a piston that’s still coming up in its compression stroke.

All matter, including gasoline, heats up when compressed. Gas preignites because in engines with higher than normal combustion chamber pressures, whether it’s because of high mechanical compression ratios or pressures boosted by a torbocharger or supercharger, the gas can get so hot when compressed that it combusts by itself before the spark plug fires.

Most new engines have a “knock sensor” that senses the shock waves from the pinging type of preignition and can to some extent compensate by retarding ignition timing, since pinging is a secondary waverfront rather than an initial wavefront. But it’s risky to assume yours can do that, and if the preignition is knocking the engine may be destroyed before you even have a chance to boost the octane in your gastank.

I will respectfully diasgree. Running a lower octane fuel on an engine that requires it does not with dead certainty mean less power and loss of mileage.

My Lincoln Mark, in theory, uses Premium and both my old and current Mark get nothing but a steady diet of 87 with never a problem. No pinging at all, no loss of power, and no loss of fuel mileage. The spark plug tips verify there are zero problems.
My opinion is that the 32 valve/4 valves per cylinder aids in this as the spark plug is centrally located in the combustion chamber. This allows the flame front to travel outwards in all directions when combustion takes place as compared to a plug mounted to the side, which would then create a flame front that has to travel across the entire cylinder bore.

As a matter of fact, even on numerous trips to Colorado I burn 85 octane up in the mountains and not only is there no pinging or loss of power on 7% grades, the fuel economy actually increases up there. Now that one I can’t explain at all.

I’ve also got a couple of cars with modified, high compression engines and they’re perfectly happy on 87 octane even with no EGR system in place, ignition timing advanced considerably more than stock, etc.

Note the Cadillac mentioned is turbocharged (these usually require Premium) and anyone who trashes an engine due to knocking probaby shouldn’t be driving at all. Easing up on the pedal instead of adopting a dxxx the torpedoes, full speed ahead approach would have likely prevented this.

I’m referring to current engines designed for premium with a knock sensor. They’ll retard timing to run on regular, and that will cut power a bit, and (slightly) reduce mpgs. Ford even lists two power outputs for its new V8 in the Mustang, one for regular, one for premium. I remember always adjusting the timing on my car/point cars just to where they wouldn’t quite ping under load, to maximize power and mpgs. Big difference? Probably not, but it was just part of the tune-up ritual…

If you blow a hole in a piston using regular in a car “requiring” premium; will the radio talk show expert(s) pay you for the repairs on your motor? I don’t think so.

If you have a car that the mfg says requires premium and you fill it with regular you are taking a risk. Perhaps not much of a risk, but still a risk. Perhaps regular will work until you put the motor under load, such as towing, a long upgrade, or a very hot summer day. It’s your car and the gas you use is your choice.

There is a mfg recommendation that premium fuel is “recommended”. This is not the same as premium required. Premium recommended are the cars with knock sensors and computer controls that can “detune” the motor to be OK with regular 87 octane.

I have one car that says to use 91 octane or higher and that’s what I do. My other car and SUV say 87 octane regular is fine and that’s what they get.

The folks that use premium in cars that are made for 87 octane regular are wasting their money. Use the fuel as per mfg recommendations.

Caddyman, the failure would not have occurred if the driver had used the required premium fuel. GM was trying to help numskulls that insist on saving a few pennies while risking destruction of their car’s engine. That’s mighty nice of them. Note that for a car like the DeVille that gets about 20 MPG average, you save about $100 for every 10,000 miles driven using regular instead of premium. If you drive 10,000 miles per year, you save 27 cents per day using regular.

Today, right now, half the cars placarded “Premium Fuel Only” are being driven on regular fuel…No holes are being punched in their pistons, no shock-waves are lifting their heads off, no destructive forces are bending their valves. The 4 or 5 octane points just don’t make that much difference…

I think a blanked statement like that is WRONG.

My Subaru WRX with a tiny 2.0L motor putting out 227HP with a turbo it is very noticeable when you place regular fuel in and push the motor(past 3500RPM).

Many cases it may not matter for the typical ownership period of a new car owner. In the elder years 125k+ the effect of improper fuel may or may not appear. Again no definitive statement.

The owner’s manual for our 2003 Toyota 4Runner says that regular (87 octane)is acceptable,but that mid grade (89 octane) may give better performance and mileage. Since my wife always brags that she gets better mileage than I do, on one vacation I accidentally put in 89 octane. I didn’t say a word about my mistake,but thought I would have something to brag about if the mileage improved. The mileage didn’t change a bit and I was out about $2 for the fill-up.

Some years back, I had a colleague who owned a VW Microbus with the air cooled engine. He purchased his gasoline from a Clark station that advertised that their only gasoline was premium. When the valves burned out on the VW Microbus, his mechanic claimed that this was caused by using the premium gasoline when the VW was designed for regular. I thought that this was bogus, but in the interest of science, I decided to try premium gasoline in my 3 horsepower Briggs and Stratton push mower. This also seemed like a good way to get out of mowing the yard. It didn’t make a bit of difference in the way the mower ran and 18 years later, the mower still runs.

I am a cheapskate, but if I owned a vehicle where the manual required premium, that is what I would put in the tank.

If “Premium” tested at 100+ octane like it once did, and “performance” engines had 10.5 compression, I would use Premium too…But that is not the case today. Paying .20 cents a gallon more for 92 octane is, well, not necessary…

I think there used to be two different octane ratings: 1) motor method; and 2) reseach method. As I understand it, the rating today is the average of the two. Some years back, Sunoco had blending pumps where one could select the octane for the engine in the car. There were charts by the pump that gave the recommended octane. I had a Rambler and could run on “sub-regular” and save one cent on each gallon over the regular offered at other major brand stations.