alsyli

Last year, the "Check Engine" light started going off intermittently on my 8-yr old Accord. A few months later, it failed its smog inspection. The dealer said I had to decarbonize my exhaust (which wasn't cheap) and said that using cheap, low-quality gas likely added to/caused the problem. No more low-quality gas for me, no thank you....

BTW, does anyone know if Chevron and United are connected? I go to what looks like a Chevron station, but the LCD screen says, "Welcome to United Oil!" Hmmm...?

F18BEN

I have 2 2012 Mercedes with this new Blue Efficiency gas engine. The leased car gets 87 and the one I own gets 91. I see absolutely no difference in performance or mileage. I just don't want to gamble with mine.

Live Oak

Back in the good old days, the 1960s and 1970s, living in New Mexico at 5,000 feet or higher, and when gas cost 27 cents a gallon, my V8 cars would specify regular gas, and buying premium was simply a waste. HOWEVER, I could move the spark advance to > 13 degrees BTDC and WOW! The power and mileage would increase terrifically!!

But that was good only at 5,000 feet of elevation. On a trip to Los Angeles, for example, on Route 66, once I left Kingman Arizona, and made the dive down to Needles, California, the car would begin pinging horribly, and I would have to pull off the road, get out a 3/8" wrench, and rotate the distributor back to its normal position of around 10 degrees, or whatever normal was, and leave it there until I returned to the upper regions once again.

Today's cars somehow sense the octane level of the gas, as well as the environment, and adjust ingnition advance automatically. Thus, I wouldn't be a bit surprised if my E Class could consume the much cheaper 87 octane with no trouble at all, as long as I stay up here where it's hard do breathe. It would be nice if Mercedes would tell me so, but I'm sure their lawyers won't allow them to do so.

CEB

My BMW ran perfectly fine in Colorado Springs on the local 87 which the car senses as 91 at that altitude.

ImInPA

What your dealer told you is simply BS. You cannot judge gas quality by brand name.

alsyli

I'm perfectly happy to admit that I'm wrong, but can you explain *why* what my dealer told me is "BS"?

BTW, he didn't say to go w/ the brand name, he said specifically to go w/ top-tier gasoline (http://www.toptiergas.com/retailers.html). Certainly the oil companies might all be in cahoots w/ each other, but I can't understand why the service manager would be part of it....

ImInPA

Gasoline stations are served by distribution centers. One center may provide many different stations and brands with fuel from the same delivery truck. If you think that if you go to an Exxon station your are always getting an Exxon product, you are mistaken. I had a friend in the business and learned a lot about what is actually going into my tank. Now, that said, there are quality differences in gasoline. You just cannot be assured what you are getting simply by brand name. I remommend frequenting busy stations. That way you are likely getting gasoline that is fresher. Gasoline does not age very gracfully.

speedgoat

In all the Mercedes, BMW and Audi's I've ever had, I have yet to notice any difference in performance or fuel economy between regular and premium. I'd like to hear what problems other people have had running regular in these cars.

speedgoat

Again, what sort of engine problems do you expect that I will have over the course of my lease that will make my decision to use regular "foolish?" Based on past experience, I expect to have none.

Arrie

I have tried 87 in both of my past cars Audi Q7 and the E350 and it was very noticeable on both of them how engine power went down, so did the gas mileage. Have not tried on my current E550 and have not thought to do so either. I believe after two cars.

But both of the cars ran just fine with 87. No issues at all with anything other than the power part and fuel consumption.

CEB

You probably don't keep your cars long enough to be able to assess long term damage.

Correct. The ECU will compensate to prevent any pinging or immediate catastrophic damage but you will note a significant drop in gas mileage and power. OTOH, if you use the lower octane gas from new then you won't notice the difference.

sosh

MB says 91 Octane minimum, PERIOD. Anything less you become a test pilot. Besides the savings for running sub standard fuel is a pittance.

speedgoat

I ran a Audi A6 (also required premium) to 190k miles almost exclusivly on regular. Engine ran well when I sold it. On my current leased mercedes I agree that I will never have them long enough for any long term assesments (company cars on a 1 year lease).

I tried to see if I can get any diffrent fuel ecomony on a previous BMW and it got 20mpg religously with any grade of gas over several fill ups.

My current c250 is getting 28 and the e350 23 mpg. Seem's to be about the same as everyone else is getting (there are several hundred of these cars at my work) and most others use premium.

I agree the savings are not much. Over both cars I use about 100 gallons a month and there is $.20 difference between 87 and 91 octance here so I save $20 a month or about $250 a year. Not much, but I still would like to know i get some benefit for that $250 and bassed on past experience I just dont see any. I'm not recommeding any one else go against the sacred owners manual, just responding to the original post on what I use...

2slowcdi

Newer gas cars have Knock Sensors to retard the timing when low octane fuel is used.
The Knock Sensors do what gear Heads did with a timing light.
If your Knock Sensors never go out you will most likely never know how far the timing is backed off.
If you have a knock sensor fail with low octane fuel in the car , it could be costly.

My last gasser was a Land Rover with a big cam ported heads and a remapped ECM.
The fuel made a big difference , when ethanol came a long my Rover lost 15% mpg so the ECM was sent to the UK to get remapped yet again , the cost was $1200 just for the remapping and around another $400 for shipping so $250 a year is just a little to pay for a free car to drive.

mnje350

To address the ethanol question. . .

I am not a chemical engineer but have read from many technical sources that ethanol has a lower BTU content for the same measure of gasoline. Meaning, lower performance and lower MPG than the same amount of gasoline. Also meaning more gallons required for the same amount of miles driven. When mixed with gasoline it reduces the amount of miles per tank of fuel. However, it does mean less oil purchased from all sources. But you have to buy more gasoline/ethanol to go the same distance as pure gasoline. I am not sure what the overall savings is.

Diesel, on the other hand has a higher BTU content than gasoline. Hence the higher MPG of diesel engines. It also explains why it is used in heavy equipment of all kinds. With the design of modern diesel engines virtually all of the drawbacks of diesel use have been eliminated.

High concentrations of ethanol will damage seals, fuel lines and other fuel system components. Modern redesigned fuel systems mitigate this problem with ethanol however.

-WARNING, MY POLITICS BELOW. STOP READING IF YOU DON'T GIVE A SH*T-

I am not sure ethanol is a good alternative to fossils fuel. Especially given the fossil fuel necessary to convert vegetable matter to something that will burn in an IC engine. I like the diesel concept much better.

PS. I don't have a diesel Benz. I wish I did though.

speedgoat

I understand and agree with the above. I also own a 1999 camaro with cammed LS1 and the ECU is dyno tunned for 91 octane premium. The timing will not retard if i use 87 and it will create detonation. Regular is not an option here. With the 2 mercedes however, the cars seem to do just fine...

Arrie

About the ethanol in gas.

In cold winter areas ethanol heps to keep water from collecting and freezing in the fuel system. In winter time you will have some sort of alcohol in the gas or you will be adding it yourself or you won't be driving.

Alcohol also, I believe, is used to set the octane rating of the fuel. This is why normally gasoline, which does not have ethanol in it, costs more as the other chemicals that are used for octane are more expensive.

El Cid

The main problem with ethanol is that it attracts/absorbs moisture. That is why it cannot be shipped via pipelines and must be transported in railroad cars.
Ethanol adversely affects rubber and plastic, which is why it is so detrimental to small gasoline engines (lawnmowers, trimmers, etc.).
Studies have shown that ethanol lowers MPG, lowers performance and does NOT lower the cost of gasoline. As of now 40% of all corn production in US goes for ethanol. The other 60% goes for animal feed, people food, export, syrup products and all other uses. With the current drought, expect all food products (including meat) to go up as more and more corn is wasted in the production of ethanol.
As far as I know, there is NO alcohol in gasoline, except for maybe race cars using special blends of fuel.
I know a guy who manages a tank farm. All the fuel products (except ethanol) come through the same pipeline, but are separated depending on type. While the gasoline may be the same, the difference is the additives that are added to each truck before it departs. This is what makes the brand difference.

CEB

Additionally, it should be noted that there no such thing as "mid-grade" gasoline. Gasoline is shipped as premium or regular and is mixed to "mid-grade" at the pump.

I did a fairly exhaustive unscientific study a few years back about different gas grades and mileage.

I owned a R32 and had the occasion to take a daily 3 1/2 hour each way trip for a trip on interstates. Because of the schedule, I left before traffic and came back after traffic.

The R32 called for premium gas. The first morning (I was running on fumes) I tanked up with 87 at the station where I always get gas, got on the highway immediatel and set the cruise for 5 miles over (70mph) That evening I again set the cruise and came back home. That was about a tank of gas so I again gassed up with 87 and ran the same sequence. The next three days I ran 91 octane.

I always gassed up at the same station. I took notes and manually calculated gas mileage each day.

The weather conditions were similar each day and the route was identical. I made no detours.

The results were quite surprising as I got a solid 2mpg more using premium. I believe that was based on the fact that about half the trip was in the mountains and the gas mileage dropped significantly with the 87 when the engine had to work harder.

You may wish to try the same experiment to see how much octane ratings affect YOUR car.

brauhaus313

Google "octane rating" and "compression ratios." I'll give you a headstart. The 2012 E350 has a compression ratio of 12:1. There should be a FAQ sticky in this forum for these kinds of questions.

This thread is filled with so many differing anecdotal, secondhand, or irrelevant accounts and opinions that its become worthless.

mnje350

Thanks for your "opinion" brauhaus313. You fit right in by your own definition.

I will go out on a limb and suggest that the OP was soliciting alternative opinions and thoughts since min octane rating is specified on the car and the manual. That's the purpose of this forum. You really don't need to do a google search to know what MB wants you to use.

But hey, that's my opinion.

brauhaus313

You're welcome, but I'm afraid it's not my opinion that the car has a 12:1 compression ratio. It's fact. The OP's question has a technical answer as to why at least 91 octane should be used. The answer doesn't lie in whether other people do or not.

Panties unruffled?

Arrie

Octane rating affects the car by what the engine is made to run with. If it is a high compression engine, like the most car engines in the world now are (Europe, Far East) it can make a big difference with the octane. If the engine is made to use high octane you will see a drop in fuel mileage if you run low octane gas. You will also feel lack of power.

If the engine is designed to run 87 like most U.S. cars at least used to be you will not see gas mileage improvement if you run high octane gas. This is simply because the engine was not designed for it. It is waste of money to use high octane fuel on a car that was designed to run with low octane.

And another fact is that all gas regardless of octane rating has the same amount of energy in it. Hig octane does not have more energy than low octane. It is all about how the engine behaves with it.

Most or perhaps all Japanese (or Far East) cars advertice that they run 87 octane fuel. This is because they can use it and they understand that people around will pick the car that can be run with it. If they would fill up with the premium fuel they would feel power increase and without themselves knowing would also get better fuel mileage, which would offset the higher price at the pump.

The engine does not know where it is, i.e. if it in the mountains or not. The sensors measure and adjust things like fuel injection accordingly. With low octane fuel high compression engine cannot take as much fuel in as it would pre-detonate. This means that a cylinder cannot produce the same "kick" as with the high octane fuel. This also means the efficiency from the cylinder goes down, i.e. you miss some forward movement from the fuel you burn. With high octane fuel the cylinder can take the maximum amount of air and fuel for maximum compression for the maximum "kick" for the maximum power and gas mileage.

Arrie

Never heard of the fact that ethanot must be transported in railroad cars...and I don't believe the explanation either. If ethanol could be pumped from ground like oil and natural gas I'm sure it would be in pipelines just the same.

It is not a problem that ethanol attracts water. I really don't think it does either but what it does is it mixes in water very well like alcohols do. This is exactly why alcohol is used in cold winter areas as a fuel additive to mix in the water that always exists in gas station tanks and end up in cars, and "burn" the water thru the engine. This keeps water from collecting in the fuel tank and freezing up the fuel system.

Alcohol as a fuel in car is more expensive in two ways. One is that it costs more, the other that gas mileage goes way down. I used to have a FlexFuel Tahoe and filled it a few times with E85. Gas mileage went down to just barely over 10 mpg when it normally was 16 - 18 mpg. But I did this to clean the engine as E85 really cleans the pipes.

Alcohol is corrosive for some materials but that is why the materials should be changed to be able to handle ethanol. This is not rocket science.

Alcohol does not make gasoline cheaper but it makes it less expensive when used just for octane boosting purposes.

mnje350

Not quite. I was referring to last sentence of your prior thread. Clearly an expression of your opinion.

Based on the title of the OP, "What fuel do you use?", it would suggest anecdotal information, opinions and facts are all welcome. If he had asked ,"What fuel should I use", your rant would be appropriate. So lighten up.