Fuel type for M113 AMG engine question. (2006 C55)

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goblintinkerer

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May 7, 2023
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Location
belfast
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2007 w203 c220 cdi
Got a C55 recently as I always loved the idea of a big engine fitted into a smaller saloon. Driving it back to where I live in the countryside has only the standard fuels available at my local garages. I read the owner's manual and it recommends to use Super Unleaded/RON98, which is also labelled on the fuel filler cover. The manual also says that if there isn't 98 available, I can use Premium Unleaded/RON95. The nearest fuel station where they have 98/99 is a 60 mile round trip. Is it ok to use 95 for long term?
 
Got a C55 recently as I always loved the idea of a big engine fitted into a smaller saloon. Driving it back to where I live in the countryside has only the standard fuels available at my local garages. I read the owner's manual and it recommends to use Super Unleaded/RON98, which is also labelled on the fuel filler cover. The manual also says that if there isn't 98 available, I can use Premium Unleaded/RON95. The nearest fuel station where they have 98/99 is a 60 mile round trip. Is it ok to use 95 for long term?
It will “probably” be fine, but best avoided if you can. Do you not even have a 97 RON fuel close by? How about a Tesco petrol station, they usually have 99 RON.
 
It will “probably” be fine, but best avoided if you can. Do you not even have a 97 RON fuel close by? How about a Tesco petrol station, they usually have 99 RON.
Tesco near me don't do any fuels. Only Asda and all they offer is 95 and B7
 
I’d brim the tank with 98/99 at every opportunity when passing :)

I’m not familiar with your location but I guess it must be quite remote, Belfast city itself must have quite a few Shell/Tesco filling stations?
 
I’d brim the tank with 98/99 at every opportunity when passing :)

I’m not familiar with your location but I guess it must be quite remote, Belfast city itself must have quite a few Shell/Tesco filling stations?
i live in county fermanagh. i think it autofilled belfast for the location :rolleyes:
 
I read this engine has a knock sensor which will adjust timing based on the fuel that is used. Worst case scenario there will be a small performance loss but the engine will be fine. I searched couple other forums about this to eliminate bias. I saw people use similar era performance cars with 95 long term where the manufacturer recommends 98 and haven't had any issues.
 
Use super unleaded whenever you can. Relying on a knock sensor to routinely protect the engine through retarded ignition timing is not the best strategy IMHO.
 
Years back on older cars you had a trim plug so you could switch between different fuel grades.

I wonder if the OP could have a remap to detune performance based on long term supply issues with the correct fuel?
 
The 'fine if you don't thrash it' advice is utter bollox.

I have owned 4 AMGs for over 10 years, all have been run on 95 with 98 when I know im going to thrash it. never have I had any issues at all.

My first CLS55 is still going fine some 7 years after I sold it with no issues. (it was on 110k when I sold it)

Our 95 Ron over here is far better fuel than what you get in a huge portion of the world.

99% of the time people are driving to the shops or back from work, not sub 10min laps around the Nurburgring.


Utter bollox? - if you say so, not sure why you feel the need for such a hostile response. You are more likely to have issues with Timing chains etc.
 
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Where abouts in Fermanagh?

Texaco around Enniskillen have 97. Hard to find apart from that. My e55 seems to be happy on 95 when I can’t get anything higher.
 
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99% of the time people are driving to the shops or back from work, not sub 10min laps around the Nurburgring.
Which is where the detonation risk is - 'thrashing it' is irrelevant.
It's all in the linked thread (only needs reading).
 
95-RON regular unleaded fuel will “probably” be OK, and like all risks it will be OK right up until the moment that it’s not OK, but unfortunately that’s a moment too late.

That moment may never come, but if you do something for long enough even unlikely risks will manifest, and it could happen at any time, not necessarily way-off in the future.

As @Bellow mentions the greatest risk is not when most people expect it, ie at high revs, instead it’s under load at low revs, and that can happen any time.

In the OP’s case I would personally use an octane booster so I’m not persistently counting on the knock sensor to save the day as it may become faulty without warning.
 
It will be perfectly fine on 95, just dont thrash it.
95-RON regular unleaded fuel will “probably” be OK, and like all risks it will be OK right up until the moment that it’s not OK, but unfortunately that’s a moment too late.

That moment may never come, but if you do something for long enough even unlikely risks will manifest, and it could happen at any time, not necessarily way-off in the future.

As @Bellow mentions the greatest risk is not when most people expect it, ie at high revs, instead it’s under load at low revs, and that can happen any time.

In the OP’s case I would personally use an octane booster so I’m not persistently counting on the knock sensor to save the day as it may become faulty without warning.
Part-load, mid-revs, cruise can also be a really problematic area of operation for some engines. Under cruise conditions, knock can go unnoticed and occur for extended periods resulting in damage (pitting) to the piston crown and combustion space surfaces. In severe cases, this leads to pre-ignition which can be catastrophic.

At high revs, there isn’t much time for knock (which is a post-spark event) to occur before the exhaust valve opens.

That @KillerHERTZ has not encountered problems using lower octane fuels doesn‘t mean that the engines in his cars were undamaged (unless they were stripped, examined and given a clean bill of health). Equally, they may have suffered no damage at all - a bit Schrödinger’s cat on this one.

Using the correct grade of gasoline when possible is a much better strategy than routinely relying on the knock sensor(s) to protect an engine tuned for higher octane, during operation on fuels with lower octane.
 
I've been down the 'does it really need super unleaded?' road in a previous thread... My opinion is twofold: 1) I am fairly certain my mpg is about 1 or 2 better and that pays for the higher cost of 98 ron anyway, and 2) I am 95% certain using 95 ron will do zero harm because the engine is from 2005 and not 1975. My owners manual says you can use 95 ron temporarily and that "this may reduce power and increase petrol consumption. You must avoid driving at full throttle". My own opinion is that most people who own these cars don't even realise they're supposed to be putting in 98 ron. 100s of these cars have done 100k+ easily, with no reports of 95 Ron causing damage. I think the reason for Mercedes insisted on super unleaded is because they wanted the owner, and more importantly motoring journalists, to experience the full power. For track use or use by journalists flooring the throttle constantly, it undoubtedly makes sense to use super, but for 95% of the time just pootling around with the occasional flooring it down the slip road or overtaking manoeuvre which is over in seconds, I think 95 is okay. But like I say, I've been monitoring the last few tanks and I'm fairly sure it's doing better MPG on super... but that is to be confirmed by Fuely in a few months
 

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