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Discussion Starter · #1 ·
My Honda 90 hp outboard runs on euro 95 (petrol) and I've got a big 110 liter tank. When I haven't used it for six or more weeks I put euro 98 in the thank (about 30) to compare for the drop in octane rating. When I googled for "high octane rating" I found that a too high octane rating ain't that of a problem (a too low one makes your engine pingle and is bad on the long term).

Does anybody how fast the octane rating drops and if a to high octane rating is a problem?
 

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Just use 95 octane unleaded. You would need a chemistry set and a degree in chemistry to tell the difference between 95 and 98 and your engine is not that clever or come to it that fussy. The drop off in the volatilizable quality of petrol in 6 moths would not be a problem let alone 6 weeks.

I remember from my early days in the motor industry when 5 star was available, we often had to do valve jobs for blokes that had "Always bought 5 star 'cos it's good for the engine". You could never convince them that just because it was more expensive it was not better and in most cases very harmful in their
Austin A60.

Afishionado
 

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six weeks will be ok with 95 ron fuel, but any thing over 4-6 months then putting in 98 ron wont hurt
 

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My Honda 90 hp outboard runs on euro 95 (petrol) and I've got a big 110 liter tank. When I haven't used it for six or more weeks I put euro 98 in the thank (about 30) to compare for the drop in octane rating. When I googled for "high octane rating" I found that a too high octane rating ain't that of a problem (a too low one makes your engine pingle and is bad on the long term).

Does anybody how fast the octane rating drops and if a to high octane rating is a problem?
Does octane rating drop in fuel over a period?
Can't say I have ever noticed or heard of that happening to the detriment off any vehicle I have owned left for longer tha a 6 week period.
 

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octane rating of fuel will drop over time, normaly if the tank is breatherable eg a car it will drop at least 2 to 3 point over a 4-6month period, but if the can is sealed then this will be a lot longer for this to happen.

the main problem is if the engine has a high compression ratio and detontion can take place if not carefull. most 4 stroke outboards has a CR around 9 to1 which is not to high so shouldnt cause a problem, weres most 2 stokes has a high cr of around 10-11/1 which may cause a problem of efficiantcy but to be honest i wouldnt worry to much.

all i do i keep rotaing full fuel cans which are sealed.

but if you havent used it for six months say and you still have a half a tank then fill up with tescoes super plus which is cheep as diesel so wont sting your pocket.

dont bother with octane booster as its expensive for what it is, i know as i use it in my mini turbo when doing drag racing at the pod ect.

either that or just use old fuel in your lawn mower lol
 

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octane rating of fuel will drop over time, normaly if the tank is breatherable eg a car it will drop at least 2 to 3 point over a 4-6month period, but if the can is sealed then this will be a lot longer for this to happen.

the main problem is if the engine has a high compression ratio and detontion can take place if not carefull. most 4 stroke outboards has a CR around 9 to1 which is not to high so shouldnt cause a problem, weres most 2 stokes has a high cr of around 10-11/1 which may cause a problem of efficiantcy but to be honest i wouldnt worry to much.

all i do i keep rotaing full fuel cans which are sealed.

but if you havent used it for six months say and you still have a half a tank then fill up with tescoes super plus which is cheep as diesel so wont sting your pocket.

dont bother with octane booster as its expensive for what it is, i know as i use it in my mini turbo when doing drag racing at the pod ect.

either that or just use old fuel in your lawn mower lol
Interesting! So what causes the drop in octane? Evaporation and the resultant mixture left I guess, but what is the process?
 

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I have done a bit of internet research on this octane rating reduction thing. :blink:

Sales of Encyclopedia Brittanica must have dropped like a stone since the internet came along!:yucky:

Fascinating!
Conclusion? Nothing to worry about and certainly not over six weeks!:uhuh:
 

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Discussion Starter · #8 ·
Thank you for the info, I'll just put in euro 95 next time. I've got a breathable tank, but usely use the boat each month. But I've still got a question for the Hogster, what is tescoes super plus? And why is it so cheap.
 

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us in the high powered mini world use alsorts of high octane fuel as this helps when running high boost preasure in our cars to avoid detonation (pimking) whilst in a NA engine it does damge but very slowly weres turbo application will wreck an engine in seconds.

but back to the fuel people like shell super plus but at the time it was only 97 ron and cost7 p a ltr more than 95 ron unleaded but uses a expensive octane booster.

tescoes superplus 98 ron fule uses different technique to get the octane rating up that is why it cost less it is actually the same price as diesel ( thats why i use it because im tight lol) but did notice the car ran alot better on it.

but for the boat world 95 ron unleaded fuel is the norm and not realy worth putting 98 ron fuel all the time as the engines ign advance curve is set up for 95 ron fuel
 

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us in the high powered mini world use alsorts of high octane fuel as this helps when running high boost preasure in our cars to avoid detonation (pimking) whilst in a NA engine it does damge but very slowly weres turbo application will wreck an engine in seconds.

but back to the fuel people like shell super plus but at the time it was only 97 ron and cost7 p a ltr more than 95 ron unleaded but uses a expensive octane booster.

tescoes superplus 98 ron fule uses different technique to get the octane rating up that is why it cost less it is actually the same price as diesel ( thats why i use it because im tight lol) but did notice the car ran alot better on it.

but for the boat world 95 ron unleaded fuel is the norm and not realy worth putting 98 ron fuel all the time as the engines ign advance curve is set up for 95 ron fuel
Hi Hogster is that Mini as in the cars?
If it is I had one of the 850cc? I think ones. My first car. 70 was a struggle and very scary. Certainly could have done with a boost! What a turkey!
 

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yes mate the car, mine is a 1380 cc turbo pumping out 152bhp goes bloody well i must say
 
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