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Which Fuel Grade?

27K views 30 replies 17 participants last post by  veeeight 
#1 ·
Hi All,

I'm about to purchase a W177 A35 but I notice it take 98 RON which I believe is the premium unleaded and rather expensive.

Q - What fuel grade does everyone else use? and does it really matter for everyday driving?
Q - Whilst I'm at it how is the UK tax?

Cheers
 
#2 ·
The car will run on 95RON(Standard unleaded) but it much prefers 97/98 RON. As a test I looked at MPG for a few tankful's of normal unleaded vs the same number of tankfuls of super unleaded. The Super gave much better MPG, which more than offset the extra cost, so not only did it work out cheaper it also gave me more peace of mind.

UK Tax. Ask us again on December 13th :)
 
#3 ·
Interesting real world comparison, NJS. I'm surprised it makes such a noticeable difference. I think the premium fuels tend to contain more cleaning additives as welI which is another good reason to use them. We don't do huge miles so run all our cars on 98 RON and I think the small extra cost is worth it.
 
#5 ·
I fill up with Shell V-Power which is 99RON. On the occasion I've used Tesco Momentum (99RON) or BP Ultimate (97RON) when no Shell station was nearby. I've never used 95RON in my A35 yet. Having said all that I'm one of the lead footed individuals who likes to drive about in Sport+ a lot. Consequently my MPG is not great - avg 27.4 mpg over the last ~4k miles according to the Mercedes Me app. Thankfully I have a fuel card - PHEW ?
 
#6 ·
I've been running 95 RON Shell the last couple of months and have seen no noticeable difference to consumption or performance, still at 35 mpg overall after the last 1500 miles on 95 RON and 9000 miles total.

What I have noticed is 14 pence per litre less at the pump. From what I've experienced it is rather difficult to see how the fuel consumption would increase so much on 95 RON to more than eat up that 11% price difference, particularly when there is only a 4% RON difference between the two fuels to begin with.

That kind of energy drop per unit volume appears to be all but indistinguishable with normal driving, which isn't exactly demanding much from the engine.
 
#8 ·
For sure. I've honestly never understood people who opt for expensive performance cars then use RON95 to refuel, even though the manual says RON98. It's as if the engineers who made the car don't know what they're talking about.
 
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#11 · (Edited)
If you want all of the 306hp (or more) available, you have to use 98RON.

If you're not bothered about all of the 306hp, stick in 95RON, the ECU will retard the ignition to cope with 95RON, but you won't be getting 306hp.

You want more power, you have to use the higher octane fuel.

(In modern turbo cars, the MON rating is more relevant than RON. The MON figure is derived from a more demanding test, more reflective of todays engines, with slightly higher RPM, higher head loads imposed during testing. )


Interesting Honest John article about Supermarket Fuel, and 95 v 98:

 
#14 ·
Guys and Gals, I really wouldn't use Tesco 99 Ron fuel or any supermarket fuel to be honest. A couple of months ago I put in the Tesco stuff, where I normally use Shell V Power exclusively, and almost immediately after the car through up a check engine light. Following diagnosis, it was found to be a faulty O2 sensor, post cat. I know that this could be coincidental, but strange that this happened after three years of trouble free motoring, where the only fuel I used was Shell.

For me, it's not worth the risk with supermarket fuel, just to save a little money.
 
#15 · (Edited)
I run my A45 on Tesco 99 exclusively (I might put Shell V-Power in every 10th tank if I’m passing), and have a tuning box, so get around 420bhp, regularly enjoy max acceleration and drive the car hard.

I would say that your sensor failure is probably co-incidental.

All fuel, supermarket or branded, is refined together and stored together at the same refineries across the country.

Tankers of all brands draw the fuel from the same storage tanks, the only difference is each driver punches in a specific code which dispenses the company’s unique additive pack.
 
#16 ·
I would tend to agree with @veeeight . It's highly unlikely one fill up of Tesco's Momentum 99 (I think that's what it's called) would cause any kind of fault in your car by itself @Chow Gar. Must be a coincidence
 
#17 ·
i used Tesco Momentum for the A45 the M235 and even now on the DMS mapped 320 and have had no issues what so ever
 
#21 ·
#22 ·
Hello Everyone

I would love to see a dyno of one of these cars comparing the two fuels as i am sure there must be a difference, One thing i notice is more pops and bangs on the lower octane oddly enough but i cant really feel much difference performance wise.
anyone else have any comments?
 
#24 ·
For a stock car I would recommend you go with RON98. For a Stage 1 or even more go to the higher to get the most power of each HP.

Here in my country of the Alps, we have the choice between SP95, SP98 from all majors stations.
Then you have BP with the SP98 ultimate which I guess is a RON100
Finalyl you have as well the Shell VPower RON102
The more RON you take, the more you pay.

So I will go only for BP Ultimate for my future MB.
 
#25 ·
Do you not have a supermarket equivalent. Many of us use Tescos Momentum 99.
 
#26 ·
Tesco is not available in Switzerland. BP and Shell, Tamoil and Socar are the main brands for gaz. Otherwise it's COOP it's a supermarket here.
 
#27 ·
I've posted this on the A45s part of the site about potentially juggling fuels in the current at pump shortage in the UK
 
#29 ·
Where's the post. Has he withdrawn it?

Personally, the fuel situation is getting so ridiculous now that I might just fill up with any super unleaded when I get to quarter tank as the fuel in the A45s just evaporates with in town driving, as though there is a hole in the tank.
 
#30 ·
Just a quick question, using 95 Ron fuel doesn’t cause any harm to the car at all does it? Because in my area iv tried 9 different fuel stations and can’t find any sort of super unleaded in this fuel crisis, so I have no choice but to use 95 ronz standard fuel
 
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