Because of the price surge. Anyone doing the same?

 

Which car do you have? Generally it's a bad idea for a Mercedes.

 

2018 C300

 

let's see how pinging goes with lower grade...
take it easy!
let's see how ECU adapts ...

 

Haha, nope that is a terrible idea for a 2018 C300, especially with summer around the corner. The car needs 91 octane.

 

Recent discussion on this already and many more in the past, consensus is don't do it. https://mbworld.org/forums/glc-class...glc-300-a.html

 

If that extra $5 a tank is going to break someone......

 

Since I discovered my car pings on 91 octane I can't imagine how bad it would be on 87. Or I should say it retards timing to stop the ping, but retarding costs you power and mpg, and makes the already very hot engine run even hotter. It will also pull boost so I lost a hella lot more power than the retarded timing.
The only way to tell for sure what it's doing it use a tool to collect data, but I'd bet $ you're already losing power and mpg on premium.

I collect data and it takes about 25-30% Ethanol, mixed with 91 octane, to stop ping. If I were to use 87 octane I est it would take about 50% Ethanol.

Or, if I just wanted to add enough E85 to 87 to net 91, then it seems it would need about 27% Ethanol. Based on your local fuel prices you could calc the net cost per gal. Ethanol gets less mpg so you'd need to calc that as well. How much less will vary but I run about 50% Ethanol and mpg drops about 20%. I'd assume 25% Ethanol would cost me about 10%? Note the mpg difference will vary car to car so you just have to run it and find out.

My car is not flex fuel and the mpg reading on the dash cannot compensate for Ethanol so it says I get the same mpg no matter what my mix is. In fact, it can't correctly read mpg period, so even on gas it reads about 10% high. No doubt a marketing trick because every car I've had reads high, and everything revolves around profits so of course they skew the #'s to make the car look good. To get my mpg I measure the amount the fuel used over several weeks, or months, to get an average.

Now that gas prices have gone up, $6.20 where I live, a typical top off of 91 octane costs $90, but with 50% Ethanol it costs $65. But I have to factor in the $65 fill only gets me 80% of the mpg. So I save maybe $10 a fill?
If you used 87 and 50% eth it would save a lot more $, but can you car run 50% Ethanol and not complain?

Here's a handy website to estimate the octane of however much E85 you add.
https://morepowertuning.com/pages/emix

When I first started playing with Ethanol I noticed it occasionally had an issues at about the 30% mark. What would happen is STFT (short term fuel trims) would go to 25, and 25 is far as mine goes. So if it sat at 25 for too long, or perhaps it was at 25 but still lean, the ECU apparently faulted the O2 sensor out. I suppose it assumed the O2 was broke or something, but it never gave a code or check eng light. Restarting the eng reset it back to normal.
I never noticed any negative effects, but when it did this I would restart it so it was ever like that for long.

You can collect data with a cheapie OBD dongle on Amazon for $10 and a $5 phone app like Torque Pro. Worth a look-c imo. At the very least to see how much it retards on 91, then put 87 in and see what happens.

 

Maybe you should consider a Honda Civic. They run regular, even if you get the 1.5L turbo.

 

Or mazda tbh you have a choice between 91 or 87 in the turbo version.

 

Thanks for sharing your findings, I mean honestly 91 is the way to go minimum for these high compression engines. Every step of the ignition process is important and why risk it and have any sophisticated step go wrong?

 

Where I am, the price difference between 87 and 93 octane is about $1 USD per gallon. Thank goodness I don’t drive as much as I once did, but I would not risk damaging the engine to save $16 or $17 per fill up.

Believe me, if it was safe to use 87 octane in your Mercedes, Mercedes would use that as a marketing thing. Clearly, it is not safe.

 

Put in 5 gallons of 87 and 10 gallons of 93. That will make 91 octane. The more you drive, the more you save!!

 

According to ChatGPT, that is the correct formulation. Using $3.79 for the cheap stuff and $4.69 for 93 octane gives me an average of $4.39 per gallon. (I will have to see how much 91 octane is selling for. There is a station near me that carries 87, 89, 91, and 93.) So, I save 30¢ per gallon or $4.50 per 15 gallons. Depending on how much you drive, that could add up. But already the news is reporting oil prices plunging. We’ll see.

 

So wait - it is safe to use the "flex fuel" that Shell advertises in a regular mercedes?

 

omair00: How much you can add will vary car to car, but I've been doing it since at least June 2022, which is when I started documenting my mpg.
I don't know about Shell. I use Pearson E85 which is 83.3% +- 1-2% year round. And it is because I'd see any change in my fuel trims.
I started at 20%, then 30%, which is where I noticed the trims issue. Yes I count the 10% that's in the gas.

I then tweaked the ECU a bit to not do that thing I mentioned where the short term fuel trims hit 25. I won't bore you with the details but I can now run >60% Ethanol without issue. I typically try keep it ~52-54% Ethanol.
Part of my original issue is my trims were already at 10% on gas, so it wasn't that far to hit 25. If unfamiliar, trims are a fuel adjustment. 10 means it's adding 10% more fuel than the ECU thinks it should. Ethanol has less power per pound so it has to add more to get the same power. 50% Eth means it's adding about 25% more fuel.

Another thing is that trim issue only appeared under certain circumstances, so it rarely happened. When it happened it was almost always when I'm stopped on a hill, like at a light, and I use the gas to hold the car, not the brake. Why do I do that you ask? Because I get bored and do stuff like that to entertain myself. Why does the ECU not like that specific condition? It's a bit complicated and it doesn't really matter, but I can explain if you want to mod the ECU. A couple months ago I drove it with the ECU bone stock and >52% Eth and it was fine, but I didn't stop on any hills either.

I'd run straight E85 but my fuel pump can't keep up because I both make more power than stock and am richer, so I use >50% more gas than stock at full throttle. Then add 25% on top of that to run 50% Eth so I'm basically flowing twice as much as stock. If anyone wants to comment on that, I have the data to show it, so don't bother.
How much Ethanol a different Benz can handle I don't know, you just have to add more and more until you run out of fuel pressure, or some issue.

Another issue is older cars may not like Ethanol, which is why Flex Fuel cars have better fuel lines and rubber parts etc that won't be damaged by it. I couldn't tell if I had the better rubber and what not but figured odds were good? Time would tell and so far no issues. Yours is two years newer so I would assume your parts are at least as good as mine? Knowing what I know now, and if your car was mine, I'd probably dump straight E85 in just to see what happens. I can guarantee most would not agree with me on that, but that's likely because I don't see cars the same as most. To me a car is a toy that happens to double as transpo. Like any toy, if I break it I fix it or get another, I'm just not overly concerned about it. Others, like my grandparents, wouldn't do anything the mfg or dealer didn't specifically recommend. I, on the other hand, ignore pretty much everything the mfg or dealer says. So it's up to you, but you know what I'd do.

 

I think Shell uses Pearson. I'll start by adding ten percent to a nearly full tank of regular unleaded. Sound good? I also don't use the brake much. I drive pretty slow, and shift between Drive and Neutral.

 

Maybe they do, but if they say they change the mix based on season it would make it difficult to figure out how much you're adding and what octane you net. The statement on my E85 being 83.3% at all times could be a local thing, since it doesn't get cold where I live. I'm certain changing to less Eth where it is cold is an emissions thing. They want those Cats at operating temp as soon as physically possible, even if it uses more fuel, shortens eng life and wakes up the neighborhood. Fyi I also adjust that annoying cold start issue, so my car starts/sounds normal when I start it. I live in a super quiet hood and I do not want to wake everyone up every morning, but part of why I adjusted it is engine life.

Another thought is the remainder that is not Ethanol is not normal gas, but very low grade to the worst of the worst. Depending on where I find info it's anywhere from 84 octane to as low as 50. This is why I wouldn't want E50, but they don't sell it anywhere near me so I can't even test it out. I'd have to assume E50 doesn't use 50 octane gas or it would be too low, but if it were 70 it could pass as pump gas, but useless for us.
So I figure I'm 50% Ethanol 50% 88 octane. The 91 octane I buy is actually 88 with 10% Eth to net 91. This mix should net me 96 at bare minimum, but I think it's closer to 100 because I was also able to bump my spark timing up quite a bit. even with more boost.
If you buy E85 where they change it to 51% in the winter, do they add better gas to it, or continue using the worst of the worst? Btw they sell testers if you want to check Eth %, but I'd imagine the gas station would know, or their supplier?

So if I were you I'd collect data to see what's happening, which I think I mentioned, and it's only about $15-20 to do this. You really just need the fuel trims and spark retard to tell you how much Ethanol is in there and if it's enough octane. You can also see the gas tank level in % to better calculate how much E85 to add. This is what I do, e.g. 18% means I need 14 gal, and 8gal E85 and 6gal 91 nets ~52% Eth. I always add the E85 first because it makes it easier for me. I note 8.0 gal E85, then whatever gas it actually took to fill, eg 5.9gal. That way I can calc the actual % via an Excel sheet I made that also gives me actual mpg. It can also calc the cost per gal or fill of the mix compared to just gas. I can share that Excel if you want it. If you're good with Excel you might even improve it for me.

 

That is way too much calculus for me. I'm an algebra major (bad joke). It's not cold where I live. Should I add the ten percent to premium fuel instead?

 

If you use that link I posted you can est the octane, but basically if you only added 10% (2.3 gal) to = E20 then I'd mix it with 89, which should = 91. I'd only use 87 if I added 4 gal (E27) to again = 91.
This is assuming your E85 is 105 octane per the calculator on the website. If they do the "Winter Blend" then I can't really help other than say add more E85. The problem is you won't know the octane unless you data log to see how the ECU normally reacts to 91 to compare the two.

As for PotatoHead's comment; if MB said the cars need 94-95, which I believe they do, it would impact sales. MB only exists for one reason, and that's to make $. So I believe whatever the premium octane is in the US is what MB will put on the gas cap door of US cars. I'd imagine the car would run on 87, it would just run hotter, get a little less mpg and probably a chunk less max power. I'm kinda curios what mine would do on 87, but I'm pretty sure I already know. I also know I'm not curious enough to do it.
Octane requirements also depend on engine and ambient temperatures, so driving through Death Valley a 2pm in summer with 91 makes it ping a lot more, and the same drive mid winter at 2am when it's freezing it probably won't ping at all.
My friend has a newer Jeep and he said it pings all the time, because he can hear it and it drives him nuts. For whatever reason the ECU doesn't retard to make it stop. I have never heard a Benz ping.

I'm sure that's all TMI, but the gist is I'd try not to let octane fall below 91 and make it worse, but if it were me I'd shoot for 94-95, which would be 7 gal E85 mixed with 87. Price that out compared to pure 91.
Today my fill was $65, if it had been pure 91 it would've been $91. Per my Excel sheet

Here's another caveat; Ethanol burns faster so it "can" cause slight ping, or more ping, at lower rpm and low loads. I didn't have an issue, but when I advanced my timing to use Eth I was not able to advance it at all at very low load/rpm range, then the higher the load and rpm the more I could advance timing. At full load and rpm I'm >10 deg advanced compared to 91.

 

We are talking about pinging as if it’s no big deal. But it is. It can be very destructive to the engine. That’s why modern engines are equipped with knock sensors. If you are actually hearing the pinging, then you have serious problems.

 

Are you saying that if I use cheaper gas, I should put more flex fuel? Or vice versa?

 

Potatoe;
It is no big deal in that the eng retards spark to stop it before you even hear it. Imo they only have knock sensors because of the EPA, who pushes and pushes for more mpg while octane drops over time. So they use a computer as a bandaid to run the eng with less octane that it needs.
Could be worse and end up like my buddy with his Jeep Grand Cherokee that audibly pings since he drove it off the lot. I suggested he add some E85 to see if it stops but he's not that kinda guy, and of course there's no way he'd let me adjust the tune. You know the type, only does what the mfg says.
I'd say >99.9% of people are unwilling to add E85 to a gas only car. Besides myself I've never personally seen anyone do it. I've only read about it online and chat on forums, all of which were for hotrodding purposes. Up until last month there was no reason to mix it for any other reason because they price it so the cost per mile is about the same as gas.


omair, use the link. And again, I think you should data log since you are playing with something you know nothing about. I'm pretty sure you plan on adding Ethanol and not check anything at all. I think odds are good you could add 4 gal E85 to a tank of 87 and be fine, but no guarantees. Or what if you add 4 gal at every fill, do you understand what that does?
Without data you won't know the Ethanol %, or if your fuel trims are ok, or fuel pressure, or temps.

 

It just sounded like you were saying that if you use cheaper fuel, you put in more flex fuel; which sounded backwards. So I was trying to confirm. Simple question.

 

That’s why I said that if you hear it, you have serious problems.

Bad gas or low octane is usually the cause. But it can ping and misfire on over-boosting, as well. It is not normal for Mercedes engines to audibly ping.

Twice in my life have I had a car ping. Once when I was a kid and put the “new” unleaded gas in my dad’s ’73 Plymouth Duster and once when I got some bad gas in my 1995 Ford Windstar.