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Smart cars and octane


SuiteSuccess
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I’ve always put 91 octane Premium gas in our smart since new, but got to researching and this is suggested  not mandatory and apparently it will run just fine on 87 octane without damaging the engine.  Just may not be as efficient.  Any thoughts on this as prices skyrocket?

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Carl, the smart uses high compression engines for which the higher octane is spec'd. Lower octane may self ignite during compression stroke which will place some additional stress on the engine. I suspect the there’s sufficient design margin to allow “some” use of low octane fuel. I think you’d be real hard pressed to find a Daimler authority to define the those limits.

When we were in AK, high octane became real hard to find a couple times and we ran with 87 octane without notable impact. Having said that, IMO it’s a bit like asking how lucky do you feel?  Not worth taking the risk on a continuous basis as we’re hoping the smart will take us to the finish line. 

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53 minutes ago, Jim & Wilma said:

Carl, the smart uses high compression engines for which the higher octane is spec'd. Lower octane may self ignite during compression stroke which will place some additional stress on the engine. I suspect the there’s sufficient design margin to allow “some” use of low octane fuel. I think you’d be real hard pressed to find a Daimler authority to define the those limits.

When we were in AK, high octane became real hard to find a couple times and we ran with 87 octane without notable impact. Having said that, IMO it’s a bit like asking how lucky do you feel?  Not worth taking the risk on a continuous basis as we’re hoping the smart will take us to the finish line. 

This is what prompted the question.  In several sites, “pinging” was discussed and felt to be a relic of the past in most modern engines.

“Dave Schembri, president of Smart USA acknowledges premium fuel is recommended however he said “you could use regular gas — there’s no damage to the car.

Edited by SuiteSuccess
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In 'Muricun cars, the knock sensor may adjust the ignition timing to compensate for low octane.  However, It's been my experience that European vehicles aren't as forgiving.  We've had four Euro cars and 3 Euro motorcycles.  All took premium fuel, and were unhappy with anything less.  Snooty things, they are.

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28 minutes ago, GeorgiaHybrid said:

The 2016's and up use a high compression ratio that is recommended to use premium fuel. However, the Hillbilly versions sold in east TN are reputed to run on kerosene, diesel or high test shine.

See quote above and maybe comment?

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8 minutes ago, SuiteSuccess said:

This is what prompted the question.  In several sites, “pinging” was discussed and felt to be a relic of the past in most modern engines.

“Dave Schembri, president of Smart USA acknowledges premium fuel is recommended however he said “you could use regular gas — there’s no damage to the car.

In my background, unless the design authority said running low octane was  within design basis for extended life, I’d not give it a whole lot of value.  I have no doubt lots of folks successfully run low octane but I also doubt you’d find anything resembling a statically valid analysis supporting the statement that “there’s no damage to the car”. 

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Another look at the question is to consider risk v reward.

Risk, not easy to quantify.  Let’s just guess it’s one in a hundred cars per year, running low octane, see a related engine failure. At todays prices, a reasonable gen 3 might be had for $10,000 and the old car gets towed to the junk yard. 

Reward could be saving $0.50/gal between the prices of regular and premium.  If you drive 10,000 miles a year and get 50 miles/gal, that’s a savings of $100 dollars a year. But you’re not going to get 50 miles/gal anymore.  Say you lose a reasonable 5% efficiency because of early ignition, that’s about 10 more gal of fuel a year, or say $40. Total reward is maybe $60.

So under these assumptions, for a $60 “bet”, you’ve got a one in a hundred chance of “winning” $10,000. I’d call that a bad bet.

You can play with the numbers and tilt it for a better “payout”. But, how lucky do you feel and is $60 worth it?

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Not sure how or IF this is true mostly due to my testing methods were not on Smarts.  When my Father was an SKP(90s) he was introduced to Lubri-Gas while on the road.  He was traveling in a '94 Dolphin with an F-53 chassis sporting the 460 V-8 and a Banks Powerpack.  He told me he found it ran better with Lubri-Gas and regular unleaded.  I got some for my "work"(I am coming to dislike this word) cube van that had a 12' box on a Chevy van chassis, 350/350 setup.  I bought it(the van) and found it got around 5.4MPG.  Not acceptable and being a technician went on to make changes and measuring MPGs after each change.  Now this van carried alot of construction equipment so it wasnt a delivery van that was emptied each day.  When I completed most of the changes, tires, carb rebuild, exhaust etc., I got it to about 9.8MPG.  Then started running Lubri-Gas and found better throttle response and improved MPG, up to 12.2MPG.  That was a pretty nice change, esp to my pocket book, BUT gas wasnt nearing $5/gal back then.  It was claimed that Lubri-Gas could offset the octane boost in premium fuel, so I ran it on regular and LG for as long as I had it.

Not sure IF that additive would help Smarts but might be worth a test, its still available.  

In my diesels I run Howes.  Anybody suggest what works best in D13s?  I have some Howes sitting around and I am wondering IF it would be OK to use it in the Volvo.

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1 hour ago, Jim & Wilma said:

Another look at the question is to consider risk v reward.

Risk, not easy to quantify.  Let’s just guess it’s one in a hundred cars per year, running low octane, see a related engine failure. At todays prices, a reasonable gen 3 might be had for $10,000 and the old car gets towed to the junk yard. 

Reward could be saving $0.50/gal between the prices of regular and premium.  If you drive 10,000 miles a year and get 50 miles/gal, that’s a savings of $100 dollars a year. But you’re not going to get 50 miles/gal anymore.  Say you lose a reasonable 5% efficiency because of early ignition, that’s about 10 more gal of fuel a year, or say $40. Total reward is maybe $60.

So under these assumptions, for a $60 “bet”, you’ve got a one in a hundred chance of “winning” $10,000. I’d call that a bad bet.

You can play with the numbers and tilt it for a better “payout”. But, how lucky do you feel and is $60 worth it?

Very nice analysis Jim. Thanks 

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If all else fails, read your owners manual. This is what ours for our 2016 says: 

"If standard (91 octane) unleaded gasoline is unavailable and you have to refuel with unleaded gasoline of a lower grade, observe the following precautions: Only fill the fuel tank to half full with regular unleaded gasoline and fill the rest with premium-grade unleaded gasoline as soon as possible. Do not drive at the maximum speed. Avoid sudden acceleration and engine speeds over 3,000 rpm."

Now we typically do not drive the maximum speed the car can go, but I do sudden acceleration and I am sure the RPMs go over 3000. If I had to use less than 91 octane, I would just have to drive with a lighter foot!

Edited by Star Dreamer
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21 hours ago, rpsinc said:

In my diesels I run Howes.  Anybody suggest what works best in D13s?  I have some Howes sitting around and I am wondering IF it would be OK to use it in the Volvo.

I've been running Howes in my D13 for almost 3 years and @ 51,000 mile haven't had any issues.

Ken....

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Thank you for the input.  A quality lubricant cant be bad as they all need some of that in the fuel system, at least that is my thinking.  But not wanting to introduce a product that hasnt worked for someone already.

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On 3/8/2022 at 9:42 PM, Star Dreamer said:

If all else fails, read your owners manual. This is what ours for our 2016 says: 

"If standard (91 octane) unleaded gasoline is unavailable and you have to refuel with unleaded gasoline of a lower grade, observe the following precautions: Only fill the fuel tank to half full with regular unleaded gasoline and fill the rest with premium-grade unleaded gasoline as soon as possible. Do not drive at the maximum speed. Avoid sudden acceleration and engine speeds over 3,000 rpm."

Now we typically do not drive the maximum speed the car can go, but I do sudden acceleration and I am sure the RPMs go over 3000. If I had to use less than 91 octane, I would just have to drive with a lighter foot!

I drive mine like I stole it. It just too much fun to drive. 

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