What octane rating do you use?
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Joined: Apr 2006
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
Perhaps I should be embarrassed to admit this...
My 2001 C320 had the 3.2L engine (91 octane required)... Sometime after 2005, there was a large, seasonal gas price increase, which prompted me to try a tank of 89 octane. I noticed a 10 minute period of peculiar performance as the onboard computer adjusted. Thereafter, the engine resumed its performance level as before. Curious, after a couple tanks of 89, I tried Regular 87. The car did not like 87 at all, but refueling at half tank level with 89 the performance was back to normal. I used 89 octane thereafter, until the car was sold last month. No problems at all (for 18 years).
The 3.5L in the E350 is a further development of the C320's 3.2L. The only reason I have not tried 89 in my E-Class is that I shop at Albertsons/Tom Thumb grocery stores, where I earn $1.00 off per gallon with my grocery purchases. So the price for Premium (93) minus the dollar per gallon is always less than the non-discounted pump price for midgrade (and regular, too). So, I've stuck with Premium since I acquired the car in 2018.
Each time we get a huge spike in gas prices, I'm tempted to try mid-grade 89, just to see what happens, although I seriously doubt there will be any ill effects. But so far, I've resisted.
So there, I've admitted it. Shoot me.
My 2001 C320 had the 3.2L engine (91 octane required)... Sometime after 2005, there was a large, seasonal gas price increase, which prompted me to try a tank of 89 octane. I noticed a 10 minute period of peculiar performance as the onboard computer adjusted. Thereafter, the engine resumed its performance level as before. Curious, after a couple tanks of 89, I tried Regular 87. The car did not like 87 at all, but refueling at half tank level with 89 the performance was back to normal. I used 89 octane thereafter, until the car was sold last month. No problems at all (for 18 years).
The 3.5L in the E350 is a further development of the C320's 3.2L. The only reason I have not tried 89 in my E-Class is that I shop at Albertsons/Tom Thumb grocery stores, where I earn $1.00 off per gallon with my grocery purchases. So the price for Premium (93) minus the dollar per gallon is always less than the non-discounted pump price for midgrade (and regular, too). So, I've stuck with Premium since I acquired the car in 2018.
Each time we get a huge spike in gas prices, I'm tempted to try mid-grade 89, just to see what happens, although I seriously doubt there will be any ill effects. But so far, I've resisted.
So there, I've admitted it. Shoot me.
Last edited by DFWdude; Dec 1, 2023 at 10:48 AM.
MBWorld Fanatic!
Joined: Oct 2002
Posts: 4,976
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From: Cincinnati
2010 E350 4Matic
Perhaps I should be embarrassed to admit this...
My 2001 C320 had the 3.2L engine (91 octane required)... Sometime after 2005, there was a large, seasonal gas price increase, which prompted me to try a tank of 89 octane. I noticed a 10 minute period of peculiar performance as the onboard computer adjusted. Thereafter, the engine resumed its performance level as before. Curious, after a couple tanks of 89, I tried Regular 87. The car did not like 87 at all, but refueling at half tank level with 89 the performance was back to normal. I used 89 octane thereafter, until the car was sold last month. No problems as all (for 18 years).
The 3.5L in the E350 is a further development of the C320's 3.2L. The only reason I have not tried 89 in my E-Class is that I shop at Albertsons/Tom Thumb grocery stores, where I earn $1.00 off per gallon with my grocery purchases. So the price for Premium (93) minus the dollar per gallon is always less than the non-discounted pump price for midgrade (and regular, too). So, I've stuck with Premium since I acquired the car in 2018.
Each time we get a huge spike in gas prices, I'm tempted to try mid-grade 89, just to see what happens, although I seriously doubt there will be any ill effects. But so far, I've resisted.
So there, I've admitted it. Shoot me.
My 2001 C320 had the 3.2L engine (91 octane required)... Sometime after 2005, there was a large, seasonal gas price increase, which prompted me to try a tank of 89 octane. I noticed a 10 minute period of peculiar performance as the onboard computer adjusted. Thereafter, the engine resumed its performance level as before. Curious, after a couple tanks of 89, I tried Regular 87. The car did not like 87 at all, but refueling at half tank level with 89 the performance was back to normal. I used 89 octane thereafter, until the car was sold last month. No problems as all (for 18 years).
The 3.5L in the E350 is a further development of the C320's 3.2L. The only reason I have not tried 89 in my E-Class is that I shop at Albertsons/Tom Thumb grocery stores, where I earn $1.00 off per gallon with my grocery purchases. So the price for Premium (93) minus the dollar per gallon is always less than the non-discounted pump price for midgrade (and regular, too). So, I've stuck with Premium since I acquired the car in 2018.
Each time we get a huge spike in gas prices, I'm tempted to try mid-grade 89, just to see what happens, although I seriously doubt there will be any ill effects. But so far, I've resisted.
So there, I've admitted it. Shoot me.
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Joined: May 2012
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From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
I know I've mentioned before. I have a friend that is a supervisor at Shell distribution, and he claims Mid and Super are both 91 octane here in his area.
The additives are the only difference in the the two, that and the labels that say 89 on the mid grade and 93 on the super.
The additives are the only difference in the the two, that and the labels that say 89 on the mid grade and 93 on the super.
Also, these cars can adjust to run 89 octane, but not regular, unless its a flex-fuel car, in which case it will run on regular or E85, the gas mileage and performance will suffer, especially with E85, which is why the flex-fuel cars come with bigger gas tanks, different spark plugs and ignition coils.
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From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
That is made by Sunoco, it will make little difference over 93 octane gas as your car cannot adjust ignition and spark that far out of range to make any difference, you would have to program the car to run that fuel, turbo boost as well to see any gains. Lead is not used anymore, you would have to add it, like for old cars.
Last edited by pierrejoliat; Nov 27, 2023 at 02:49 PM.
MBWorld Fanatic!
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
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From: Charlotte, NC
Had: 1987 300TD, Had: 2004 C230 Sport Sedan, Have: 2014 E350 Sport, Have: 2019 S450
We have run mid-grade (89) in our 2014 E350 since new. Now has 138k miles, and never has a problem.
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From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
One thing here to realize is the type of the fuel supply in the engine, port injection vs. direct injection.
With the “old fashioned” port injection fuel octane rating is very important as the fuel/air mixture sees the high compression before the ignition spark. We don’t want the fuel/air mixture to ignite before the spark so we need high octane rating of the fuel.
DI engines are a bit different for this. Fuel is not mixed in air outside the cylinder so it is only air that sees the high compression before the spark.
Fuel is injected in the high compression cylinder just at the time of the spark or just a microsecond before that. Danger for knocking is minimal regardless of the octane rating or at least way lesser problem compared to the port injection. This all makes me wonder if I should try a tank of 87 to see how it runs in my DI engine.
With the “old fashioned” port injection fuel octane rating is very important as the fuel/air mixture sees the high compression before the ignition spark. We don’t want the fuel/air mixture to ignite before the spark so we need high octane rating of the fuel.
DI engines are a bit different for this. Fuel is not mixed in air outside the cylinder so it is only air that sees the high compression before the spark.
Fuel is injected in the high compression cylinder just at the time of the spark or just a microsecond before that. Danger for knocking is minimal regardless of the octane rating or at least way lesser problem compared to the port injection. This all makes me wonder if I should try a tank of 87 to see how it runs in my DI engine.
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From: Virginia
W212 M276 DELA 30 ; W211 M113k, W126 M117, W126 OM617, W211 OM642 ; R107 M117 X2, Sierra 1500 LZ0
I've run premium in every gas MB I've ever owned. On my diesels I'll actually seek out higher cetane than what is available in most places near me (40). I've found between 45-50 cetane at various gas stations in Virginia. In my older M117 powered cars, I've removed the timing retard resister that was shipped with US spec cars to accommodate lower octane fuel which gives me a bit of a bower pump if I maintain discipline about using higher octane. Well known mod on those older engines.
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From: MA
2008 E350 4Matic, 2011 E350 4matic
You basically need an engine designed to take advantage of the higher octane and that's more of a purpose built engine, using higher octane in an engine not designed to take advantage of it doesn't really do anything.
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From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
Not sure about the better part, only an electrical engineer here. Basically octane is ability to resist detonation. If you don't have detonation at a lower octane, then a higher octane isn't better if there's no detonation to begin with. Higher octane just costs more money so I would say higher octane is actually worse because it costs more money without adding any extra benefit. It'd be different if the btu content of higher octane gas was higher and therefore there's more energy in the fuel, but it's basically the same. You can only retard, advance timing so much and if you're already at the ideal setting, advancing it just makes it worse not better.
You basically need an engine designed to take advantage of the higher octane and that's more of a purpose built engine, using higher octane in an engine not designed to take advantage of it doesn't really do anything.
You basically need an engine designed to take advantage of the higher octane and that's more of a purpose built engine, using higher octane in an engine not designed to take advantage of it doesn't really do anything.
MBWorld Fanatic!
Joined: May 2012
Posts: 2,359
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From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
One thing here to realize is the type of the fuel supply in the engine, port injection vs. direct injection.
With the “old fashioned” port injection fuel octane rating is very important as the fuel/air mixture sees the high compression before the ignition spark. We don’t want the fuel/air mixture to ignite before the spark so we need high octane rating of the fuel.
DI engines are a bit different for this. Fuel is not mixed in air outside the cylinder so it is only air that sees the high compression before the spark.
Fuel is injected in the high compression cylinder just at the time of the spark or just a microsecond before that. Danger for knocking is minimal regardless of the octane rating or at least way lesser problem compared to the port injection. This all makes me wonder if I should try a tank of 87 to see how it runs in my DI engine.
With the “old fashioned” port injection fuel octane rating is very important as the fuel/air mixture sees the high compression before the ignition spark. We don’t want the fuel/air mixture to ignite before the spark so we need high octane rating of the fuel.
DI engines are a bit different for this. Fuel is not mixed in air outside the cylinder so it is only air that sees the high compression before the spark.
Fuel is injected in the high compression cylinder just at the time of the spark or just a microsecond before that. Danger for knocking is minimal regardless of the octane rating or at least way lesser problem compared to the port injection. This all makes me wonder if I should try a tank of 87 to see how it runs in my DI engine.
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Mercedes-Benz GLC300 2019
Octane levels in winter
Just out of interest, the other day I heard a radio report (yes, I still listen to the radio!) discussing the cost of living and the recent fall in inflation rates across North America and Canada. One of the contributory factors was said to be a decrease in gasoline prices, due to the gas companies changing to a (cheaper) fuel mix for winter driving. Certainly I have noticed a fall in gasoline prices for the last month or two; I'm now paying less than I was in September.
Does anyone know if this would affect the octane rating, and possibly the performance of our cars during winter months?
Does anyone know if this would affect the octane rating, and possibly the performance of our cars during winter months?
MBWorld Fanatic!
Joined: May 2012
Posts: 2,359
Likes: 1,555
From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
Just out of interest, the other day I heard a radio report (yes, I still listen to the radio!) discussing the cost of living and the recent fall in inflation rates across North America and Canada. One of the contributory factors was said to be a decrease in gasoline prices, due to the gas companies changing to a (cheaper) fuel mix for winter driving. Certainly I have noticed a fall in gasoline prices for the last month or two; I'm now paying less than I was in September.
Does anyone know if this would affect the octane rating, and possibly the performance of our cars during winter months?
Does anyone know if this would affect the octane rating, and possibly the performance of our cars during winter months?
MBWorld Fanatic!
Joined: May 2012
Posts: 2,359
Likes: 1,555
From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
An engine designed to run on premium fuel, will not burn regular as efficiently, usually some type of dished piston is used to reduce this in cars designed to run regular in direct injection. hence more unburned fuel will be pushed out the exhaust valve into the exhaust system, this can mess with O2 sensors.
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From: Occupied Palestine
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Correct me if I'm wrong, but the reason DI is high pressure is because the gas doesn't get squirted in at the start of the compression stroke but rather near the end. So there's no chance of low octane fuel igniting early. If it was squiring it in at the start of the stroke it'd be low pressure just like port injection. I believe a lot of modern DI engine also use the Miller cycle, which has all the advantages of Atkinson but without the weird connecting rods.
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Joined: May 2012
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From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
DI is high pressure, making the fuel delivery more precise and to atomize fuel better, also because it's being introduced to the cylinder under compression, yes. So there would be LESS chance of pre-ignition. Miller cycle indicates intake valve remaining open and pushing some air-fuel mix back out the intake valve, I believe you would need a scroll-type supercharger to facilitate that, a turbo would not produce the boost necessary at lower RPM's
Also I would add the ignition and combustion cycle is different here than in Europe, I believe the flex-fuel cars here have a similar sequence to those Euro cars.
Also I would add the ignition and combustion cycle is different here than in Europe, I believe the flex-fuel cars here have a similar sequence to those Euro cars.
Last edited by pierrejoliat; Nov 29, 2023 at 02:27 PM.
