omair, I did explain it. If you want to run 87 to save $ then it'll take 4 gal of E85 in the tank to bring the octane back up, per the calculators in the link that don't seem to want to use. They're very clear. If you don't want to use the link, or don't understand it, it makes me worry you'll end up with too much E85 in it. How much is too much I don't know but it is, potentially, a delicate balance between enough octane but not too much Ethanol.
I can use however much Ethanol I want but that's because I tinker with the ECU. You clearly won't, so you have pay attention to how much Ethanol you add, and imo you really need to look at what the ECU is doing so you know if the ECU is ok with it. I'm pretty sure 4 gal in a tank will fine, but I'm not 100% sure.


Potatoe, maybe we misunderstood each other. When I say ping, with these cars, I'm only concerned with causation of retard. Preventing ping prevents the excessive ECU retard. Retard also causes ping so all the more reason to prevent it. It would also be nice to have enough octane so if/when the knock sensors fail you won't hurt the eng from actual ping/detonation. Speaking of sensors, I discovered they are sensitive to the condition of the motor mounts, so bad mounts can cause excessive retard. Makes sense, but I'd imagine very few people think about that.

I've had a variety of older cars, without knock sensors, and many of them would ping thanks to the factory spark timing. One of the first things I do with a car with a distributor, especially if it has Iron heads, is set the total mechanical advance to where it needs to be, which is always more advanced than oem, often 10 deg more, then all is well. It's as if they made the spark curve correct, but retarded it to make the EPA happy.
I bumped the idle timing in my Benz >10 deg, and it makes a big difference in temps, gas or Eth mix. I also "overboost" all the time, with 10 deg more advanced than oem. Unlike oem at oem boost, no ping/retard, but that's mostly thanks to the Ethanol
My Chevota spark curve starts at 27 deg, ends at 32, + 10deg Vac, which is drastically different than oem. If it had the oem timing it would overheat quickly and ping, undrivable really. My guess is your Duster would've ran fine if the spark was correct.

 

My logic is saying if I use premium fuel, I can use more flex fuel; but if I use cheap fuel, I should use less flex. Is that correct?

 

Ethanol (E85) is higher octane than Premium (91-93 octane) fuel. Typically, E85 has an octane rating typically between 100 and 105. So, adding to any gas is going to raise the overall octane level. In the discussion here, it is suggested to add it to 87 octane.

 

@Chevota Speaking of 'retard'...I suppose a retard does not just use the proper fuel. To me this should have been a yes or no question not a freaking science experiment trying to debate or concoct special recipes for driving an average run of the mill car down an average run of the mill road.

 

OldMan, the answer is yes, but it's not simple because there is risk. We can't buy the proper fuel, but we can mix it. Or you can mix 87 with E85 to save $. Yes to both, easy peezy, but if the car is not ok with it you just might kiss the engine bye. So if he wants to save a buck and take the risk, go for it, but it's easy to check if the eng is ok with it.

I give up and can only suggest he stick to premium and stay away from mixing fuel. I tried, I'm out.

 

Stick to the OEM recommendations...

Trenton O. Gibson
tgibson@highline-autos.com
Highline Autos
Direct: 602.909.9216
Office: 480.348.0777

 

I added two gallons of ethanol to an almost full tank of regular. It was fine to begin with, but then I think I heard something going on with the drivetrain, so I topped it off with premium. I think it's fine now.

 

Great, how much money did you save with this fillup?

 

Am I understanding this correctly, that you started to experience a difference/possibly future issues almost immediately with this experiment? Honestly it just doesn't seem worth the risk in my opinion.

Trenton O. Gibson
tgibson@highline-autos.com
Highline Autos
Direct: 602.909.9216
Office: 480.348.0777

 

I don’t feel like looking it up right now (or maybe even ever), but look up part numbers for the fuel system on both flex fuel cars and normal cars, things like injectors, fuel pumps, fuel lines, etc. If there is a difference, that’s your answer as to whether it is safe.

 

The noise might have been something else. Lets just hope gas prices come down so I can stop experimenting?

 

I would advise against it. If you like your car keep it for the weekends. Buy yourself a 2014-2018 vw Passat. I have one gets 600-650 to the tank on regular. Honestly it’s a sick commuter and long distance car. I have a 20 minute drive to work. Can throw $30 into the tank and drive on it the whole week
the truck is for truck things
and Benz comes out to play on the weekends


any car can run on a lower grade fuel but it’s going to start breaking stuff. You’ll save money initially but then you’ll get f’ed when the car decides it’s time

 

Anyone know how many gallons equal a bar on the gauge?

 

Varies...when I changed my pump (float included) the gague on the dash changed, not massively...but changed. The old pump it would sit go slow to 50% then plunge - new pump is more equal....

 

Why would anyone wait for $4/gal gasoline to justify saving money? If you can save $0.50/gal when gasoline is $3/gal or when it's $4/gal, you should always be going for the $0.50 savings. I'm not advocating the use of low octane fuel when a car is spec'd for high octane. Just saying the justification based on price is irrational.

 

@streborx Huh? Why bother even looking? This is not at all diffrent from a check at a resturaunt. I do not look. I can not change it and I do not partake in things I can not afford. I simply can not comprehend how this is even a conversation on a car enthusiast website. Next are we supposed to use the cheapest oil we can find? Every repair part the cheapest that can be had? Where do we draw the line on being cheap?

 

I just paid $5.39/gal for Top Tier premium gas at the local Shell station for my 2004 Audi TT with about 255,000 miles. Based on some of the arguments lately, I should be running 87 octane without any insurance other than state mandated liability. I've always run 91/93 octane and had full coverage. I also have a 22 year old car that drives and runs well on original engine components (other than maintenance items) with over 1/4 million miles.

Hmmm, where did I go wrong?

 

I would have responded sooner but I was at GoodWill trying to find some new dress-shirts for a meeting I have coming up.....drove across town with a flashing check engine as I filled my car up wtih some free bio-fuel from a neigbors "prepper experiment". I hope the car does not burst into flames as I canceled my insuruance. Now, off to Tonys Discount Used Tires to see if they have anything to fit on my OE AMG wheels....

 

You missed my point -- I'm not advocating to buy cheap or to buy expensive. I'm asking why saving $0.50/gal makes sense when gasoline costs $4/gal, but saving $0.50/gal doesn't make sense when gasoline costs $3/gal. $0.50 is $0.50 no matter what the price of gasoline is. 87 octane fuel is the same no matter its price. Why would anyone think it's OK when it costs $4/gal, but it's not OK when it costs $3/gal?

 

so much for the plunge

 

In the UK there is no 87 octane, regular is 91, or 99 octane is available for between 10p and 30p per litre extra.
You guys in the US just wouldn't believe the price we pay for petrol here, currently about £1.60 per litre for 91 octane regular.

So 3.8 litres to one US gallon, so that's £6.08 (GBP6.08) for one US gallon of regular, which is USD 8.24 per US gallon.

What are you actually paying for regular gas today in the US ?

 

I cannot remember the last time I looked at a gas pump and really gave a damn what it said. Maybe a better option for some folks would be public transportation. We did go out on the boat a couple weekends ago and spent about $500 in less than 6 hours on fuel so my car is the least of my concerns

 

Check this out ...


BP record 2X profits (source: BBC News)

Price increases fueled DOUBLE PROFITS: that is a cool $13.Billion/Yr for private enterprise.

"The poor pay more".