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

[ALFAitalia]

Dont forget that in the UK 95 Ron has to be 95 MINIMUM to comply.......so most tests a bit higher.

 

[Bobby Dazzler]

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

Measuring over a few months might give you some erroneous results.

Measuring over (1) weeks or (2) years might give more reliable data to (1) keep conditions are consistent as you reasonably can in real life or (2) to average out changing weather and ambient conditions.

The effect of the changing seasons can have a noticeable effect on fuel efficiency. The swing in temperature alone over the next few months will increase consumption.There are other factors too, such as use patterns change.

 

[Bellow]

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.

And at that low revs the load is full torque without the throttle being anything near to fully open.
Some of you need to understand what a throttle valve is. It is a power controlling device - not a torque controlling device.

 

[philnewmerc]

Measuring over a few months might give you some erroneous results.

Measuring over (1) weeks or (2) years might give more reliable data to (1) keep conditions are consistent as you reasonably can in real life or (2) to average out changing weather and ambient conditions.

The effect of the changing seasons can have a noticeable effect on fuel efficiency. The swing in temperature alone over the next few months will increase consumption.There are other factors too, such as use patterns change.

Rest assured I won't be submitting the results to the Nature journal. Just here

 

[Bobby Dazzler]

Rest assured I won't be submitting the results to the Nature journal. Just here

Expect your consumption to get worse…

 

[philnewmerc]

"Relying on knock sensors"
The car relies on the knock sensors whether its on 95 or 98 ron.

"You need to know what a throttle is"

Mercedes state: avoid full throttle, not avoid high load at low rpm (which is a bit difficult in an automatic anyway).

But safest strategy is 98 ron plus if it does 1 mpg more that's paid for anyway the extra cost anyway. However, the idea there are 100000s of AMG ticking time bombs due to 95 ron use sounds vvvv unlikely to me

Expect your consumption to get worse…

Yes slightly, but on both 95 or 98... Never noticed a big change in petrol cars tbh tho, but quite significant in my diesels. Main challenge is being observant recording it.

 

[philnewmerc]

And at that low revs the load is full torque without the throttle being anything near to fully open.
Some of you need to understand what a throttle valve is. It is a power controlling device - not a torque controlling device.

Don't shoot the messenger but Mercedes specifically say "avoid full throttle", that's it. I would have thought high torque, full throttle, low rpm* would be worse for knocking its just that on light load its most noticeable to the human ear (only ever heard it on 1980s old bzngers on carbs).

* Full throttle full load at low rpm is possible on AMGs due to the speedshift gearbox in manual mode. I wonder if that is the scenario that Merc were thinking of to give the 98 ron warning. If in full auto mode presumably this wouldn't happen as the box just shifts down a cog.

 

[Bobby Dazzler]

"Relying on knock sensors"
The car relies on the knock sensors whether its on 95 or 98 ron.

"You need to know what a throttle is"

Mercedes state: avoid full throttle, not avoid high load at low rpm (which is a bit difficult in an automatic anyway).

But safest strategy is 98 ron plus if it does 1 mpg more that's paid for anyway the extra cost anyway. However, the idea there are 100000s of AMG ticking time bombs due to 95 ron use sounds vvvv unlikely to me

Yes slightly, but on both 95 or 98... Never noticed a big change in petrol cars tbh tho, but quite significant in my diesels. Main challenge is being observant recording it.

Knock sensors are indeed relied on with all fuels, but the likelihood and impact is greater if routinely using 95 RON on a car which has been designed/mapped for 98+ RON fuel.

How many drivers would (a) read and (b) understand if Mercedes stated the detail of the specific conditions which should be avoided, ie high load, low RPM, narrow throttle opening?

Consumption will indeed increase regardless of fuel, but those changing conditions will lead to inconclusive (or incorrect) results, ie it will outweigh 1 mpg improvement you’re currently seeing.

I suspect you probably already understand the need for consistent - if not controlled conditions - for any kind of even semi-scientific results upon which meaningful conclusions can be drawn.

 

[Bobby Dazzler]

Don't shoot the messenger but Mercedes specifically say "avoid full throttle", that's it. I would have thought high torque, full throttle, low rpm* would be worse for knocking its just that on light load its most noticeable to the human ear (only ever heard it on 1980s old bzngers on carbs).

* Full throttle full load at low rpm is possible on AMGs due to the speedshift gearbox in manual mode. I wonder if that is the scenario that Merc were thinking of to give the 98 ron warning. If in full auto mode presumably this wouldn't happen as the box just shifts down a cog.

We naturally think of a catastrophic failure, with a big bang and bits which used to be on the inside of the engine being on the outside of the engine. Whilst possible, it’s not likely.

What is more likely is wear from micro damage and pitting which accumulates over time, eventually causing problems which will not necessarily be linked to the cause of low octane fuel.

Like all risks we all make a judgement, and this is no different.

 

[Bellow]

Don't shoot the messenger but Mercedes specifically say "avoid full throttle", that's it. I would have thought high torque, full throttle, low rpm* would be worse for knocking its just that on light load its most noticeable to the human ear (only ever heard it on 1980s old bzngers on carbs).

Very probably not. At say, half of peak rpm, half throttle opening provides all the air the engine can consume (hence the detonation risk) and pushing further on the pedal wont increase air flow - but may well trigger fuel enrichment to very slightly raise volumetric efficiency (cooled, more dense air), and decrease the likelihood of detonation.

* Full throttle full load at low rpm is possible on AMGs due to the speedshift gearbox in manual mode. I wonder if that is the scenario that Merc were thinking of to give the 98 ron warning. If in full auto mode presumably this wouldn't happen as the box just shifts down a cog.

Actual 'full throttle' with less than full pedal travel (more accurately, a 100% delivery ratio) at low rpm is the predominant driving scenario other than cruising and over-run conditions. There's no avoiding it - other than accelerating such that the delivery ratio is so low which will be painfully slow and incur throttling loses and, would require constantly increasing the throttle opening concomitant with increasing speed. No one drives like that. Fly-by-wire possibly could - maybe does. But I'd want to know before slackening on octane requirement.

 

[philnewmerc]

We naturally think of a catastrophic failure, with a big bang and bits which used to be on the inside of the engine being on the outside of the engine. Whilst possible, it’s not likely.

What is more likely is wear from micro damage and pitting which accumulates over time, eventually causing problems which will not necessarily be linked to the cause of low octane fuel.

Like all risks we all make a judgement, and this is no different.

I have no evidence to refute that, and none to support it either

 

[philnewmerc]

Knock sensors are indeed relied on with all fuels, but the likelihood and impact is greater if routinely using 95 RON on a car which has been designed/mapped for 98+ RON fuel.

How many drivers would (a) read and (b) understand if Mercedes stated the detail of the specific conditions which should be avoided, ie high load, low RPM, narrow throttle opening?

Consumption will indeed increase regardless of fuel, but those changing conditions will lead to inconclusive (or incorrect) results, ie it will outweigh 1 mpg improvement you’re currently seeing.

I suspect you probably already understand the need for consistent - if not controlled conditions - for any kind of even semi-scientific results upon which meaningful conclusions can be drawn.

I don't disagree with any of that, which is why i joked about not submitting the results to Nature.