Ok, I'm sure I may get villified for even suggesting this, but for those who are using primarly Regular unleaded gas in your C, please post here with any negative effects. I WILL be using Regular unleaded in my new C, as I have done with other luxury vehicles that I have owned. (Infiniti I35, QX4, and Acura TL). I have never noticed any negative effects, other than possibly a little less Horsepower (hardly noticeable however). Some have suggested that luxury/sport sedans "require" the premium fuel simply to meet their Horsepower specs published on paper. My suspicion is that the C will run fine on the Regular unleaded, especially since it is a duel fuel vehicle, and obviously has the ability to "adjust" iteself to different fuel types, at least at some level.

 

With an 11.3 compression ratio, you are testing the engine management system's ability to prevent pre-ignition. Do you really think saving 10% on fuel is worth it?

 

No real affect that would "ruin" the car. But you are going to ruin the longevity of the car. Also you are not going to get the potential tourqe... Im shur that more members will add to the list of why you really dont wanna do this, but in the meen time Welcome to MBworld.

-Mike

 

I don't get why people do this. You buy a Mercedes-Benz and then cheap out on gas? Why bother to get a Mercedes if you don't want it to perform as intended? Using lower grade gas produces sluggish performance and no doubt an extra strain on the vehicle because the engine management system has to constantly compensate for this. Sure gas costs, but at least you guys have a C-Class, which gets a lot better mileage than a lot of other MB models.

M

 

^+1

 

the other posters here are correct. You won't see any real ill effects because the M272 engine does have a knock sensor and will adjust appropriately. This WILL however, reduce performance. Don't forget that the octane rating of E85 is 100-105.

 

Here's another thing to consider. Lets assume you drive 1000/mo (12,000/yr is average mileage) and get an average of 25mpg. If the price difference between regular and premium is $.20, you save a WHOPPING $8/mo.

 

Probably saving less than that! The de-tuned engine performance will have reduced power that will in turn require longer time spent in lower gears, which in turn will increase fuel consumption.

 

^Thats a whole MCdonalds meal... so dont act like its not alot lol.

 

noticed I used the word "WHOPPING" hahaha

 

You spend between $33K and $48K for a car and you are worried about an extra 20 cents per gallon at the feul pump?

 

wow, you guys must do alot of highway driving. My computer says i'm getting 17.4 mpg for the last 452 miles driven.

 

I dont know about you guys... but i alway put 93 in all of my cars... If i spent so much money on a car... i want it running at peek.
Plus.. I find that i get better overall better mpg compared to 91, or regular. (i track it using an spreadsheet, and everytime i fill up i record how much gas ive driven on that full tank, and the price at which i paid for 93(usually 3.29-3.40) Oh... and i go out of my way to find a cheap gas station.

 

IMO the reduction in performance and fuel economy is not nearly as big of a concern as the carbon buildup and potential damage that will occur. Most people do not care about the performance reduction and are not sharp enough to calculate or keep track of their fuel economy, but failure of the O2 sensors and cats (most common failures; carbon buildup in cylinder heads and exhaust manifolds not visible) are most common due to the reduced combustion temperatures and retarded ignition. FYI, your dealer can void your warranty if there are any related system or engine failures and you have been running regular (it happened to a friend of mine).

 

 

Well, I'm a tightwad, what can I say. And although I have not done a comparison on the C300 mpg regular vs premium, in the past with other luxury sedans I have done the comparison and seen no difference. I'm not a heavy foot power kind of guy, so I'm not really going to notice much in the power difference - if any. Also, I typically use Shell gasoline always, and have had no issues around dirt buildup.

No one has presented any real evidence of long term damage, and if anyone has any, I'd can certainly be persuaded to change my mind on th issue.

And since now one else has posted (yet) to the forum that they are using Regular, I guess I am the only one "stupid" enough to do so ?

Anyhow, thanks for the feedback, and keep it coming. I'll be sure to report when my engine blows up from "pre-ignition?".

 

I've had a mechanic friend try to tell me that modern ECUs try to run richer first when auto ignition is sensed, to try to cool the cylinders before it resorts to dialing back the timing. He also claims that because of it's nature, the knock sensor is only adjusting to a condition that is present, it is not preventing it so some auto ignition is always occuring dumping more heat into the cylinders and the oil than they would normally get. But, what I thought of later, after the conversation, is that you'd have to be under enough load to cause the auto ignition in the first place right? But load doesn't necessarily mean full throttle, it can also be lugging up a hill ... and in the PacNW we have lots of hills.

His other caution was that the new higher mileage synthetic oil ratings were based on using proper octane, and it'd be a good idea because of the extra heat, to change the oil more frequently.

He didn't mention anything about engine longevity ... both of us only keep our cars 3-4 years so we don't really care about rebuild times. We're more concerned with transmission longevity (we both had BMWs at the time and BMW automatics aren't known to last very long).

I figure, I like power and since the extra $.20 a gallon is only 5-6% more than the cost of low octane, I'd spring for it. I'm already spending way more than I need to for transportation anyway ... if I were really concerned, I believe a better way to save money at the pump is just to drive less. Compared to other cars in its power/size bracket, the C gets awful fuel economy, so I'm already spending more than I should.

Plus if I feel like slumming it, I can get better than 5-6% discount on my gas by using a grocery store or costco branded gas.

I tell my wife's grandma to use regular though. She only drives 50 miles a week and drives like a 'granny' so there's no point in her spending the money.

On the flip side, my wife accidently put lower octane in her Q7; she noticed a lot of pinging and hiccups in acceleration ... but it could've just been crappy gas too?

 

You know this how?

Mercedes has no incentive whatsoever to make you use higher octane than you need, and of course Mercedes knows more about its "knock sensor" than do you.

I would suggest those proud of themselves for "beating the system" by using regular fuel put their money where their mouths are and post their VIN numbers here--cars to avoid on the used market for sure.

 

Carbon buildup has nothing to do with "dirty gas" so the brand in this case does not matter. Carbon buildup is from ignition occuring at a colder temperature than the engine was designed for. Since regular gas ignites at a colder temperature. You are much better off buying premium gas from a cheaper station than regular shell (although I would only use top-tier gas myself).

Your engine will probably not blow up from pre-ignition, but there are a number of other possible issues that could happen, one of which happened to a friend of mine a couple of years ago.

This guy bought a new C class and ran regular in it, always insisting it was no different. Eventually he started getting some noise from the valve train so he brought it in to the dealer (still under warranty). They inspected the car and it turns out he bent a couple valves. Since they were confused how this would happen on such a new car, they checked the ECU and found numerous stored codes for pre-ignition. Now very suspicious, they analyzed the gasoline and found it to be below the 91 minimum. Since they knew not only that the gas was under spec, but that he had been using that for a long time, they charged him the diagnostic fee and voided his warranty.

I agree with LK, if you are going to continue to use regular, post your VIN so nobody here will get stuck with the car.

 

maybe I should clarify. "You won't see any immediate ill effects."

 

A friend of mine has a BMW 330i and when she took the car (lease) for service the Service Mgr plugged her electronic key into their computer and he told her she was using regular gas instead of premium. He said this will void the warranty if a related problem occurs and told her that continuing use of regular would cost her at the end of the lease when she turns in the car. I would think that MB service can see the same thing.

 

Again, why doesn't MB offer a Blutec® C in NA? If fuel and the environment are big concerns these are two great reasons to offer such an efficient clean and powerful (Torquey Diesel) in NA

 

...anyone else impressed that they can do this?

 

They just check the knock sensor. If it knocks it throws a code they can read. It is impressive what data is available from the your car today.

 

When your engine seals and engine starts knocking, you will kick yourself in the ***. High compression engines require premium fuel to prevent ignition since it take more energy to burn the gas. Would you put regular gasoline in a Ferrari or let alone an AMG?

I wish I could hit people in the head with a gas nozzle when I see them fill up 87 in a car that requires at minimum 91 octane. Why? Why? To save $2 at fill up? You are going to spend more money maintaining the car otherwise and have larger repair bills.