91 or 95 Octane Petrol: Which is best?

[Komata]

A request for the 'car buffs' in our midst ('cos I'm not a 'mechanically minded'...)

I am currently having a debate with my son as to the best fuel to use for my 'new' 2.0 litre 2006 Nissan Bluebird Sylphy, 4-door sedan which I am advised was not seen in Europe as a sedan, but built in Russia and the Ukraine and known as the Nissan Almera Classic (just in case someone owns one)

The motor BTW is the 2.0 litre Nissan MR20DE14 (in case that helps).

In my 2.0 Nissan 'Primera I always used 91 Octane, but was told by the dealer from whom I purchased the 'Sylphy, that I should ONLY use 95 Octane, and that 91 was 'bad' for the motor (although 'bad' wasn't defined).

My son disagrees, and says that 91 will work just as well as 95 (and be cheaper too).

Not wishing to 'wreck' anything, and in the absence of an Owners Handbook for my new 'toy' who is correct?

Thanks in advance.

Komata

[daveg]

No expert guidance from me but the following (quite old) link may help:

http://www.economist.com/blogs/babbage/2012/09/octane-ratings

Note what is said about 'knocking'!

I'm not sure how the new smaller, turbo charged petrol engines would use the higher octane but I have a 1600cc, 4 cylinder turbo and use 91 RON. Perhaps I should go for a tankful of the higher rate to see if there is a difference.

Enjoy your new car.

Dave G

[oscar]

When we had 4 grades of petrol, you never, ever put in a lower grade than recommended, but it was fine to put in higher grade. Lower grades burn quicker, causing more heat and burn out valves and piston tops.

Ergo, use the 95 for safety's sake.

[Oldun]

I agree with 'oscar' 

Speaking as an owner of a 54 year old classic, even then the Octane rating was important. If I run mine
on 95 octane the timing is set at 6 degrees BTDC, if I run it on 91 octane - the timing has to be set at
3 degrees BTDC.
I may be wrong but, as modern engines are more 'critical' in their build compared to older engines I would
think that the correct octane rating is important.

Some of the effects of incorrect octane rating is listed below (borrowed from a Nissan car forum)

Engine and fuel component damage;
High fuel consumption;
Excessive maintenance and servicing costs;
Overheating and piston damage;
Poor vehicle response and acceleration;
Stressful and unsatisfactory driving experiences.

Roger

[MJKERR]

2006 Nissan Sylphy 2.0
Minumum Octane rating 91
Therefore you can use either fuel grades

[Oldun]

2006 Nissan Sylphy 2.0
Minumum Octane rating 91
Therefore you can use either fuel grades

Not so sure about that. Had a word with a local car tuning outfit near me, and their
advice for that engine is 'due to the added Ethanol and the possible increase in the
future, use 95 or one of the supers. The engine will last longer and run better'

This local company service and retune mainly Japanese cars, and with the import models
will if requested retune to the original Japanese spec

Roger

[ozzie Bill.]

yes, agree with MJ, you can use 91. higher performance engines, or those MUCH MUCH older, need the higher octane. as far as I understand it, the higher performance need it for whatever reason, but the old motors need high octane as lead replacement or whatever its called these days. The Nissan does not count as old at only 2006.  All of my cars, current and recent past, run on 91, with the exception of the Volvo which is a low compression turbo and prefers the 95. cheers, Bill.

[Komata]

Thank you folks: I knew someone would know (yes, that makes sense) 

So 91 it is;  my son was right. 

He's going to LOVE that when I tell him... 

[d-a-n]

Are we talking RON or MON (research octane or motor octane numbers) here? It'll be fine on 91 as the knock sensor will take care of timing. It will run happier and possibly cleaner on 95 (the 'super' variants which come in 97-98 RON in the UK have a better detergent package for cleaning carbon deposits.)

I'm not familiar with the MR20DE14 - is it turbocharged? A turbocharged engine will always respond better to high octane fuel than a normally aspirated engine.

Older engines don't necessarily need higher octane fuel, it's all down to how advanced/retarded your ignition is. The timings stated in workshop manuals for older cars are from the days of 4 or 5 star leaded fuel which was 97 or 101 octane. RON/MON is nothing to do with lead being present or not in the fuel.

[Mr Sprue]

For what it's worth I have friend who works for Shell and basically it's all down to getting what you pay for!  The premium fuels have more additives in them to make the engine be more efficient and burn cleaner.  Not forgetting that tetraethyl lead is no longer added which protected your "top end" against wear, so the more additives you can get in your fuel the better!

Although the modern engine is now electronically controlled by many sensors, lower octane fuels can increase combustion chamber temperatures and higher cylinder pressures, a common problem with earlier engines was "pre-ignition" which is caused when the fuel burns in the engine earlier than it should do, especially if it's a low compression engine were the fuel can combust before being ignited by the spark plug.

So here's a heads up to anyone who wants to take care of their engine, the next time you visit the forecourt it's worth knowing that a fuel's octane rating equals how much compression the petrol can tolerate! So the higher the rating, the better the fuel resists combustion. Hence why the modern day high-pressure engines require more expensive fuel.

Lastly a word of warning to those of you who own a diesel car. If your not already aware do you know the petroleum company's are now allowed to add up to 10% bio fuel to the mix?  Not good stuff to be putting in your tank especially if your diesel is used a lot for local journey's, so for the sake of an extra 5p a litre it's worth filling with the premium fuel to avoid a costly bills that will await you!

As for supermarket fuels not as bad as some are led to believe, but however to keep their cost's down some additives are not included!

Happy Motoring! 

[mr bachmann]

thank god for 2 strokes 
mind you getting 30 grade or Castrol R for home mixing is getting harder .

alan

[Oldun]

mind you getting 30 grade

Try Smith and Allan (the last 3)

http://www.ebay.co.uk/sch/m.html?_odkw=30+grade+oil&_ssn=smith_and_allan&item=300854444725&_from=R40&_osacat=0&ssPageName=STRK%3AMEBIDX%3AIT&_from=R40&_trksid=p2046732.m570.l1311.R3.TR11.TRC1.A0.H1.X30+oil&_nkw=sae+30+oil&_sacat=0

[d-a-n]

thank god for 2 strokes 
mind you getting 30 grade or Castrol R for home mixing is getting harder .

alan

Did my CBT this year and thought I'd get a two-stroke Yamaha DT 125 - I didn't know they stopped making 2 stroke stuff for road use about 10 years ago!

[daveg]

They didn't have CBT back when I started driving two wheels in 1964.

I did do a what was then a training scheme run by the RAC and another organisation I remember as the Motor Cycle Union but that bit may be wrong. Anyone remember who they were?

Keep safe!

Dave G

[Wingman mothergoose]

I usually use the normal unleaded petrol in my Alfa Romeo 147 2.0, I wasn't aware we could get 91 RON in the UK, I thought normal unleaded was 95 RON and super unleaded was 98 RON.
I used to drive a 1987 Rover SD1 2.6 Vanden Plas as my daily runner, cost a fortune to run but I always used LRP(lead replacement petrol) with an additive/octane booster that put it up to 98 RON. I would use proper 4 Star petrol if I could find a garage that sold it, at the time there were still a handful that did...

Chris