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+---- Thread: Which fuel type? 91/95 or 98? (/showthread.php?tid=603)
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Which fuel type? 91/95 or 98? - Pabloako - 04-05-2023
Hi everyone,
Can I just check which fuel people are running in their busses? I have clicked around the web and some say standard unleaded (87 in USA and 91 in Aus) and some say to use premium 95/98 because it runs cooler and smoother.
What do you use and do you add any additives to keep the valves nice and happy now that we do not have lead in the fuel?
'
Many thanks
Paul
RE: Which fuel type? 91/95 or 98? - Oldman - 04-05-2023
My understanding is that VW heads were re-designed to run on unleaded fuel after the late ‘60s.
Someone here will know when the change kicked on…
Use of which fuel octane is a bit of a can of worms depending on who you talk to.
When I had my engine built in 2010, my mechanic dyno’d it with 98 and advised me to keep using it for best fuel consumption and performance. It’s a stock 2ltr with stock, rebuilt Solex carbs. and associated ancillaries. I’ve never had an issue with it and have just completed a (nearly) 5000 k round trip of NSW and SA. My bus is a Sopru Campmobile and was fully loaded for the trip and carried two adults.
It returned on average, 11.4 ltr /100 k and sat on 95kph on the tar…….the dirt roads were a different story !
Performance and cooling have a lot to do with driving style too……never “lug” your engine and always drive to the conditions, using appropriate gear choice and rev. range…. Lots to think about !
Personally, I feel the extra cost is worth it, however I have friends that say I’m crazy and use ‘91..
Like their buses themselves, everyone has their preference.
RE: Which fuel type? 91/95 or 98? - Doob - 04-05-2023
From discussion with various mechanics, and an industrial fuel chemist from BP, my understanding is as follows;
The octane rating of a fuel is a measure of the fuel’s resistance to premature detonation or pinging.
The higher octane rating has nothing to do with thermal energy of the fuel. A RON91 fuel will have the same thermal energy (power) content as a RON98 fuel.
The higher octane fuels (RON95 & 98) are an advantage for higher compression ratio engines, and for turbo changed / super-charged applications. In particular, for more modern engines where the engine ignition advance is controlled by an ECU. Such motors can take advantage of high octane fuels by optimising the ignition advance without generating premature detonation or pinging / knocking.
For old stock standard Kombi motors with standard compression ratios and no turbo charger, the higher RON rating of premium fuels is probably not a great advantage.
However, those marketing premium fuels (PULP) such as Shell & BP etc… promote other advantages besides the high octane rating. Such as lower sulphur content, and proprietary additives to enhance fuel system & engine cleaning etc.. This is where PULP may be advantage for Kombi drivers? ….perhaps!
A few years ago I had the heads of my 1971 AD Code 1600cc motor inspected. The engine specialist doing the work assured me that the standard VW heads & vales of this vintage were fine to run on unleaded fuel with no additional lead replacement additives.
Cheers
Grant
RE: Which fuel type? 91/95 or 98? - Melissa - 04-05-2023
I use 95 - never use E10 - sometimes I use 98 - especially when getting it from Costco (they do not have 95) and it is cheaper than other local service stations' 95.
RE: Which fuel type? 91/95 or 98? - Grantus - 04-05-2023
For the 1st 20 years or so, I just used 91, as suggested in the manual.
Looking after a neighbours Suburu Forester whilst they were away, they said they were getting better mileage from 95, so I tried (Caltex) 95 & 98 in my Kombi, with still the same mileage, just more expensive fuel.
The easiest and most common petrol stations close to home, are Caltex - now Ampol.
Long haul runs, I started buying BP 98 and quickly learned that my Kombi over 400kms, on BP 98, uses 6 litres less fuel, than on Caltex Vortex 98, (now Amplify 98 from Ampol).
I now plan trips around town, to include one of the few BP outlets, to fill up, as it makes pure economic sense to me, to stick with BP.
But as discussed, everyone has their own opinion, and personal choices of brand or type.
Best to just choose what works the best, for your bus.
RE: Which fuel type? 91/95 or 98? - Barry - 04-05-2023
Ideally you need to know your compression ratio
Stock is around 7:1 ……. 91 is fine.
8 to 8.5:1 ……. 95
Above 9:1………98
Never use E10 whatever
It eats rubber
RE: Which fuel type? 91/95 or 98? - Barry - 04-05-2023
There is no benefit in using a higher octane than what your motor needs
RE: Which fuel type? 91/95 or 98? - Doob - 05-05-2023
Apart from Octane rating, there has been much concern expressed about the quality (or lack there of) of Australian fuels, in particular RON91.
Most notably the high sulfur content of our RON91 compared to Europe and elsewhere. - and the effect this may have on engine components & oil, as well as the impact on environment & health. I believer there are moves afoot to improve the situation in the next few years.
Any number on internet articles on this subject - for example.
https://www.bgaustralia.com.au/news/technical-advice/australian-fuel-quality
https://www.goauto.com.au/news/conflicting-claims-about-australian-fuel-quality/2021-11-01/86245.html
https://www.carexpert.com.au/car-news/australian-petrol-getting-cleaner-from-2024-legislation-brought-forward
Cheers
Grant
RE: Which fuel type? 91/95 or 98? - Pabloako - 05-05-2023
Great replies everyone, thank you.
So far I have only been using 98, however I am making a trip to Dalby this weekend (the first trip since getting her registered and then fixing every oil leak that started afterwards).
I will try 95 next and then 91 on this trip and see if I notice any difference. It seems like the lead replacement additives are not worth it, so I won't bother with those
Edit: Crikey, I have just read the links above. I will stick to 95/98 and then I may feel a bit more environmentally conscious, whilst I burn my 14L per 100km.
RE: Which fuel type? 91/95 or 98? - DakDak67 - 05-05-2023
91 plus regular upper valve lube, but I’m just a mechanic who knows what he’s talking about ….