lamonsas

What fuel do u guys fill in your c300/c350? I put fuel for the first time this week in my leased c300 and I put super fuel (93) , since the car is leased, can I put regular fuel for the 3 year term or it will mess up the engine? I want to cut on fuel costs if it's possible.

lamonsas

??

Blazeitup123

use 91+

nothing else.

lamonsas

Why 91 and not 93?

C300Sport

He most likely meant "nothing lower".
If you do a search for fuel, octane, etc., you can find tons of threads on this subject as well as the technical aspects of what is going on in the engine, at the refineries, etc, etc.

I am Jeff

I find it hilarious how people stretch themselves to the limit, but try to skimp out on the gas. Your owners manual and even your gas cap states "Premium Required"! Follow the directions.

RLE

I agree. Funny, though, how there always seems to be plenty of bucks for "Mods".

lamonsas

ok but by premium fuel u mean 91 or 93?

hitokiri89

Use the highest octane available to you .

Samieee

Some states have 91 as premium and some have 93. Both are fine

RLE

Why don't you consult your owner's manual?

91 is what you want and anything higher is a waste of money.

lamonsas

yes i read the manual, it says to put 91. if i put 89 which is midgrade, is there a difference between mid grade and premium?

sagar350z

Hope that answered your question. If not, yes there is a difference.

lamonsas

see, if i owned the car then without a doubt i would ONLY put 93 but the car is leased for 3 years which is why im debating and dont know what to do.

Samieee

For your reference...

My stepdad leased a 535xi for 2 years and he only added regular 87 in it. The car has turbo so I thought all sorts of things would go wrong. But it never had any engine related problems. Only major issue was the HPFP but that's common. Maybe 2 years isn't long enough for problems to occur or maybe he got lucky. One thing for sure is the next owner is going to be best buds with his/her service advisor.

ImmaBeSmug2

What are you asking these guys for permission? I assure you no one will tell you didn't always put premium in the thing.
BUT. . . thanks for confirming my rationale for buying NEW only.

lamonsas

of course buying new is the way to go, when you buy used you never know what they guy who sells you the car was fueling the car with, see, you are buying a benz, not a toyota or a honda

But yea back to the point, the car is leased u know thats why im even thinking this in my head.

I want to tell u one thing though, before i leased my 2011 c300, I had a 06 C230 V6 which i owned and i ALWAYSSS put 93 in that car, never once 87, and that car always gave me a CHECK ENGINE light EVERY single year which required service to be done, it wasnt an engine problem i think cuz as the service center said it was a sensor that failed every year and it was a common problem with that car.. anyways just wanted to point that out that even if u put 91+ fuel problems happen.

I really like the idea of putting only the best in the car but if the car is leased and not really mine then thats why i even started this thread, i just wanted to ask if i put 87 or 89 the car will be fine and if i will have noticeable decrease in performance/gas milage?

Acapulco Bill

To quote from page 354 of the W204 factory manual "Fuel requirements - Only use premium unleaded gasoline. The octane number (posted at the pump) must be 91 min. It is an average of both the Research Octane Number (RON) and the Motor Octane Number (MON): (RON+MON)/2. This is also known as the ANTI-KNOCK INDEX."
The C300 and C350 engines will also run on Gasohol (10% Ethanol, 90% unleaded) if it meets the minimum octane requirement. The C300 with automatic transmission is Flex Fuel and will also run on E85 Premium (85% Ethanol) taking into consideration that each gallon contains less energy and will have lowered gas mileage.
@lamonsas, lower octane gasolines combust at a different rate, mainly because they have a wider varying combination of different length hydrocarbon molecules. The "octane" rating itself is comparison against the known (read desirable) characteristics of the 8-carbon long chain OCTANE, which burns slowly and evenly, and does not detonate prematurely as fuels with mixed-length-chain gasolines.
The lower the octane rating, the more the gasoline has a tendency to ignite prematurely, hence causing "knocking" or detonation before the piston has arrived at the top of its travel, forcing it to want to force the crankshaft to rotate backwards, which of course damages the engine.
You would have to check your lease contract to discover if you have any liability if engine damage is caused by not using the required octane gasoline. In any case, it would be logical to assume that the engine's performance and mileage economy is closely related to respecting use of fuel with a 91 octane minimum. One wonders if there is a study showing if higher octane gasolines provide better gas mileage, (possible engine damage aside), to partly offset the added expense a higher octane gasoline costs.

RLE

"The C300 and C350 engines will also run on Gasohol (10% Ethanol, 90% unleaded) if it meets the minimum octane requirement. These engines will also run on E85 (85% Ethanol) ............"

STOP!!. The only W204 that can use E85 is the C300.

The C350 is not a Flex Fuel model. See page 482 of the owner's manual.

The C300 fuel system, end to end, is designed for E85. Different fuel tanks, different oxygen sensors, different injectors and every o-ring and gasket. All E-85 resistant. It's E-10 that is OK for all models.

It is well known that using a higher octane fuel than required does not improve performance or fuel economy.

lamonsas

yea but we are not talking about E85 right? thats different than unleaded gasoline right? what are u saying in other words RLE?

Acapulco Bill

A 91 octane E85 fuel is preferable for the C300 or C350 than an 87 octane unleadad gasoline.
And any car will use more 91-octane E85 fuel than a 91-octane unleadad gasoline because ethanol has less stored energy per gallon. As long as what you fill your tank with meets or exceeds 91 octane, the engine should perform properly with no risk of damage caused by low-octane knocking.

I am Jeff

LOLZ... That check engine light is to tell you to service your damn car. lol You don't think there would be a massive recall if your sensor "broke" every year on the dot?

And yes, using 87 will cause a increase in fuel consumption and due to the ME over compensating for the decrease in octane. If you don't believe me, go try it! It's only a lease. lolz

jctevere

Just put in 91 or 93 (whatever is available in your state). Putting in anything lower will cause your car to retard timing to compensate for increased knocking, leading to less power and lower fuel economy - eating at whatever savings you will have had. Also, its just dangerous to put in regular fuel. I filled up my g37 with regular fuel once on a road trip (because that was all the station had and I was really low) and the car would keep jerking forward as I stopped, like the tranny would downshift too late (i guess because of knocking or something).

But anyway, it is really dangerous in stop and go traffic and parking lots that extra half a foot could mean you plowing into the car in front of you, costing much more than premium gas... The way I look at it, if you drive 12,000 miles per year, and premium is on average only 30 cents more than regular, and you average 23mpg (which is what I average), then over the entire year it only cost you $150 to use premium over regular gas. That isn't even taking into account the fact that you will get lower gas mileage with regular, more carbon buildup and less performance. Seems like a no brainer to me...

EDIT: I would also like to note that while the c300 and NOT the c350 can use E85 approved fuel, the c300 4Matic CANNOT! I would know, I have two, says it in big letters in the manual.

NJBNZ

I'm sure I'll get flamed for this but I have always put regular (87 octane) in my C300 since I got it and I haven't had any problems at all. Did the same for the 2005 Jag and 2007 C280 I had before and never had any problems with any of them.

We're not talking about Ferraris or Bentleys here

sagar350z

We aren't talking about Toyota's or Honda's either.