Premium Vs. Regular grade Gasoline debate

I have heard Tom & Ray repeatedly saying “there is no advantage in using Premium grade fuel Vs. Regular grade (87)” and it is an utter waste paying the extra money for the Premium grade!

I have S430 Mercedes and have been very diligent in following Merc’s recommedation on using Premium grade fuel ony!

Am I wasting the extra 25-30 cents per gal in buying premium Vs. regular?

At the “new owners” orientation, the service manager at the dealership very clearly stated that only the premium grade fuel be used for all Mercs - because

1) It burns slowly and gives better mileage (i.e. per $ spent), and

2) Becasue it burns slowly, the engine doesn’t get very hot which prolongs the engine’s life!

Your scientifically based input will be greatly appreciated.

If your manual states PREMIUM required, on your advisors statements

  1. true
  2. true

There is no debate. The owners manual says Premium Grade Fuel Only, and that is all you should use. PERIOD. end of debate. Especially with a Mercedes, any savings in fuel cost will be instantly removed with the first fuel-related repair.

Tom and Ray have stated that using premium grade in a car designed for regular is a waste of money. You get no advantage using premium in a car designed for regular. But your car is designed for premium! Using regular will cause damage!

The service advisor is correct, AND and I would advise you to follow the advice contained in your Owner’s Manual. I believe that Tom & Ray probably said that there is no advantage in using premium gas IF your engine is designed to run on regular.

If your engine was designed to run on premium gas, there are three distinct disadvantages to using regular gas:

  1. Reduced performance
  2. Reduced gas mileage
  3. Possible engine damage from pre-ignition

This is one of the few times Tom and Ray are wrong. I’ve heard them say it, too, but they are wrong.

Use premium only in your Mercedes, as the owner’s manual states.

I have heard Tom & Ray repeatedly saying “there is no advantage in using Premium grade fuel Vs. Regular grade (87)” and it is an utter waste paying the extra money for the Premium grade!

I don't think you heard the whole thing.  Tom and Ray, as well as most all the regulars here, agree that for cars that require high octane it is critical to use it as you will suffer reduced power and mileage and will likely damage the engine.  

If it is recommended, then the damage the engine part is no longer part of the picture (the car will adjust for the lower octane, but it will have reduced power and mileage.  

We all agree that if it does not specify, you can safely use regular, and may (or may not) receive some increase in power or mileage, but don't expect it. 

Becasue it burns slowly, the engine doesn’t get very hot which prolongs the engine’s life!

That is not very accurate, but the conclusion is likely true.
  1. It burns slowly and gives better mileage (i.e. per $ spent), and
  2. Becasue it burns slowly, the engine doesn’t get very hot which prolongs the engine’s life!

The fact that it burns slowly isn’t really relevant. In fact slower burning works against you as it means more of the burning occurs after top-dead-center when the combustion chamber volume is expanding.

The key feature of premium fuel is its higher self-combustion temperature or flash point. The higher the octane, the higher the flash point (self ignition) is for the fuel.

As the flame front travels from the spark plug across the top of the piston, the unburned air/fuel mixture at the far end of the piston is subject to increasing pressure (and hence increasing temperatures). The higher the self-combustion temperature is for the fuel, the less likely it is for that air/fuel mixture across the piston to spontaneously “self ignite” (which is the pinging you hear).

The service manager fibbed a bit as to why premium is required. Premium resists “pre-ignition” (predetonation), which is the fuel-air mixture exploding early (detonating), rather than burning more smoothly and slowly at the right time. Detonation is heard as “pinging” or “knocking”, and will eventually destroy the engine. Don’t use lower octane than the owner’s manual requires. Premium gas has lower energy content and gives you slightly worse mileage, and burning is burning – the engine gets just as hot.

An engine designed to burn regular gas is just wasting money on premium. The only gray area is if the manufacturer recommends rather than requires premium. What happens here is that the occasional tank of regular causes knocking, which is picked up by a sensor, which signals the computer to retard the ignition. This permits the engine to accept regular, at the cost of worse mileage, performance, and emissions. You may actually end up paying more dollars per mile than with premium! And continued use of regular will cause engine damage if the knock sensor should ever fail to pick up the predetonation.

In my opinion, the “octane spread”, 87-92 between regular and premium is not enough to justify it’s price and is not enough to cause engine damage or reduced mileage.

A cars octane demand depends on its compression ratio and virtually all cars on the road today will run fine on 87 octane fuel. More than anything else, premium fuel is a profit center for the oil companies.

Premium fuel burns slower than regular and is therefore somehow better. That is just urban legend nonsense. Once ignited, a charge of premium fuel burns at the same speed as regular gasoline.

Mercedes cars are sold all over the world including countries where premium gasoline is unknown. They somehow manage to run just fine without it.

I agree with Tom & Ray. Premium gasoline is for suckers.

Are you saying that all cars can run on regular gas without knocking/pinging? That’s not true – some cars just flat out require high octane, or they’ll knock themselves to death. Some cars (with knock sensors) run better on premium than on regular. And I wouldn’t be surprised if MBs sold in the third world are detuned so they’ll run on regular (I doubt any African country has emission standards).

Stop making sweeping statements that you can’t back up.

Here’s the way I look at it. If you purchase a vehicle that REQUIRES a high octane fuel, that engine is tuned such where a lower octane fuel will have an effect under most driving conditions. And this is when the knock sensor will take over and the computer will command a richer fuel mixture along with retarded timing to prevent the knock from continuing.

If you purchase a vehicle where it’s RECOMMENDED that a higher octane fuel be used, that engine is tuned such under most driving conditions a low octane fuel can be used. But if the the engine is brought to is extremes, the low octane fuel will have an effect on it’s performance while under those extremes. And then the knock sensor kicks in.

But if you purchase a vehicle where a low octane fuel is recommended, you don’t have to worry about this required/recommended crap!


Google mercedes benz knock sensor, knock sensor mercedes benz regular, knock sensor Loren
Beard, knock sensor car and driver, for a variety of opinions. Unlike the other respondents, I have no scientifically based input. You may want to ask your service manager if he has read the owner’s manual as a basis for his view. Conventional wisdom has it that if your owner’s manual says “Must” and not “Recommended” then use premium and also having a turbocharger will almost certainly dictate premium.

I have seen it on the 'net that there are some regular fuel vehicles with a knock sensor that will adjust the spark timing to get more power and gas mileage with premium gasoline but it did not work with ours, a GM luxury car specified to run on 87 octane.

That said, premium is only a relatively few pennies more than 87 octane now. I have to buy premium at BP stations where I live to keep the alcohol out of my gasoline.

92 is not “high octane”. High octane is 100 octane and up. AvGas was once available in octane ratings as high as 140.

If your engine will run smoothly without ping or noticeable detonation on 87 octane fuel, then you can use that grade of fuel without fear of damage regardless of what the “book” says. Few of todays drivers have ever heard “ping” or “knock” so they don’t know what it sounds like. 5 octane points is simply not worth paying that extra money for. If your engine runs great on 92 octane “premium fuel”, it will probably run great on 87 octane “regular fuel”.

Back in leaded fuel days, “regular” gasoline was posted at 90 octane and “high-test” was 100 octane or more. Amoco (Standard Oil) sold 100 octane lead-free, clear as gin motor fuel for .05 cents more than regular…

Compression ratios used in cars of that era (1955-1974) were 9 to 1 or maybe 9.2 to 1 for “regular” fuel cars and 10 to 1 or 10.5 to 1 for “premium fuel only” cars.

The ONLY time octane becomes critical is during hard acceleration. The vast majority of the time when under high manifold vacuum, cruising at a steady speed, the octane rating means nothing as the engine has very low octane demand under those conditions.

My opinion is the same as it’s always been; it depends. Every car is different and there is no one size fits all when it comes to this issue.

If these criteria are met I don’t see a problem with using lower octane. Knock sensors and EGR system operative (Check Engine Light will tell you if they’re not), no loss of fuel mileage, spark plugs burn clean, and there is no rattle during hard acceleration you should be fine.

Ninety-One octane is recommended for my Lincoln and that car has about 150k miles on pretty much nothing but 87 octane with no past or current problems, no loss at all of power or fuel economy, and no foreseen problems for the future.
I just got back from a trip to CO and as per the usual; ran 85 octane while in the mountains with zero problems or even the loss of 1/10 of a MPG in fuel economy.
(And for what it’s worth, I maintain and nitpick my Lincoln to death along with pulling the spark plugs every 15k miles for a visual inspection just to make sure everything is on the up and up.)

I think point No. 1 is debateable and point No. 2 is on very shaky ground. Keep in mind that the majority of service managers and service writers are not mechanics and the vast majority are not even mechanically inclined but you might not know this by listening to them.
JMHO anyway to use as you see fit.

i still dont understand why people who spend many thousands on buying a car,would want to put the cheapest,crappiest fuel in??in england i always put shell v power 97 octane in my 2002 ford,even though the manual says use a minimum of 95 octane, .and avoid "supermarket fuels"because a named brand petrol will have better additives in it to keep carbon deposits to a minimum,my car runs great with no pinging,and always passes the emissions test every year.

I have a Crown Victoria and a Caddy Allante, the Caddy “requires” premium fuel" but it seldom gets it…I shop for THE BEST STREET PRICE period. Over the years, this has saved me THOUSANDS of dollars. The Vic is approaching 200K miles with no problems what-so-ever burning the cheapest gasoline I can find.

The Caddy’s mileage and performance are the same regardless of the octane of the fuel, and I NEVER have detected any ping or knock…

MB requires premium as does BMW since the “regular” fuel over there is about 90-91 in US octane. 91 octane is considered premium in most part of the USA.

This is one of the few times Tom and Ray are wrong. I’ve heard them say it, too, but they are wrong.

I’ve NEVER heard them say that. What I have heard them say is…“If the car can run on regular then running on Premium is a waste. And if your car runs on Premium you should run on premium.”

Man these oil or gas threads never go away. This really shouldn’t be a debate-every car is different and has different needs. Is milk best for everyone? No some people are lactose intolerant. If your owners manual recommends premium then use premium. I have personally found that cars that benefit from premium tend to see improved gas mileage, so any savings from using regular fuel becomes minimal.

Manufacturers dread having to recommend premium fuel if they don’t have to-it doesn’t help car sales. If the car needs it or recommends it then use it.

How about this: I wouldn’t use 87 in your car, but you might be able to get away with 89. Run a couple of tanks of 89 and try to notice the following—if you hear any spark knock, or notice worse engine performance, surging on acceleration (especially when in higher gears), switch back to premium. Pretty much any modern engine has knock sensors that will prevent damage to the engine if spark knock is detected, but it my make your car’s performance miserable, and drivability aggravating. If the lower octane works fine, no harm–keep using it. Different stations (brands) have apparently different ideas about what constitutes the same octane, so you may have to shop around. I can get away with using higher octane every other fill up with no problems.