QLD
27 posts
Havent been able to get out in boat for about 7 months due to shift work ,lousy weather.etc.I have about 100 litres of mixed 2 stroke in 150 litre tank..Should I throw it out or top it up with higher octane 98 mix. All advice welcome
QLD
3 posts
Should still be OK depending on where you got if top up with best octane available, could also use an octane booster. if you are still concerned and if there is any water in the tank a cup of denatured alcohol will sort it out.
QLD
663 posts
Just smell it, you can tell bad fuel by the smell. The higher the octane in fuel, the harder it is to detonate so you are better off going for the lowest octane fuel if you want to trying "re-vitalising" the old stuff. Put it this way, when you're 10km off shore and can't get the motor to start, will it cost more than a 100l of fuel?
QLD
663 posts
Just thought I should explain a bit more:
The octane rating is often mis-understood and is thought of as similar to a magical injection of nitrous into the fuel to make it fully sick....
The reality is that the octane rating shows the fuels ability to detonate with higher the octane meaning the harder it is to detonate.
Why do you pay more for a fuel that is harder to detonate?
That is because it is more stable and therefore more efficient as it detonates at excatly the designed point in the crank cycle.
Pre-detonation or detonating too early causes a loss of power because the pressure built up before top dead centre in the piston is greater than designed so you lose the potential power from this already burnt fuel.
Detonation left too long causes a power loss too as it does not have enough time to burn all the fuel to maximum pressure before the exhaust valve opens.
Hence, running your car on more stable fuel (98 Octane) means you will detonate in the correct time and your engine will run more efficiently.
This is why I would suggest that if you want to blend your fuel, maybe you should try a lower octane and more volatile fuel so that you get a bit more "pop" out of it. If it was my engine and I thought the fuel was gone far enough off, I wouldnt waste my time on the old fuel and risk damaging the engine.
Up to you, but I thought I would just explain further as to why I reccomended lower octane fuel which may be contrary to popular belief.
If I have got any of that explanation wrong, please let me know as I am writing this off memory, not from a text book.
Cheers,
WA
1991 posts
^ That's a cool explanation.
Never knew that's why higher octane fuel is better.
Edit: Or in some circumstances "better"
WA
1227 posts
Firstly, "detonation" is definitely the wrong word and the wrong idea. The fuel must burn, NOT detonate (or explode). If your fuel detonates it will soon destroy your engine.
Secondly, how long you can store petrol is mostly dependent on how it's stored. Fuel (petrol, or AVGAS in this case) stored in sealed, airtight containers is still acceptable for use in (military) aircraft after 2 years of storage. Stored correctly, it would be fine for your car after at least 4 years I'd guess.
So, how airtight is your boat's fuel tank? If it is airtight, how much air is in there with your fuel? As someone else has already said, smell it. Stale fuel is quite easy to detect. Is there likely to be any water in there with your fuel? Add a cup of metho if you suspect water contamination.
Finally; If you break down 30+ miles out, is a tank of fuel worth it? Can you drain it to use in your car?
