How Does Petrol Go Off?

[jrzila]

Hi all,

I am newbie to boating and could not find how petrol goes off.

Can some explain please.

Also if I have some normal unleaded in the fuel tank ,does that go off? or is it once 2 stroke is mixed that it goes off. My motor has the 2 stroke directly injecting.

Can I just top up the petrol with some fresh stuff and it will be ok?

Thanks

Simon

Edited July 26, 2007 by jrzila

[Flightmanager]

Hi Simon ,

Petrol , as you would be aware , is refined from a heavy crude oil . During the refining process , the molecular structure is changed , and what we end up with is motor spirit (petrol). There are volatile substances in this mix , which tend to evaporate.Old, unused, petrol goes 'stale', smells foul, and rots tanks: the lightest fractions can evaporate whilst the remains gradually join their molecules back into heavier stuff like that they were once cracked from. This is the "gum" that befouls so many outboards that have been unused for a period of time.

I have heard that adding a premium grade to "old " petrol will restore its octane rating , but have never tried it myself. I think I would prefer to use the old fuel for degreasing etc , and run my motor on fresh fuel.

Ross

[chrisg]

Hi Simon ,

Petrol , as you would be aware , is refined from a heavy crude oil . During the refining process , the molecular structure is changed , and what we end up with is motor spirit (petrol). There are volatile substances in this mix , which tend to evaporate.Old, unused, petrol goes 'stale', smells foul, and rots tanks: the lightest fractions can evaporate whilst the remains gradually join their molecules back into heavier stuff like that they were once cracked from. This is the "gum" that befouls so many outboards that have been unused for a period of time.

I have heard that adding a premium grade to "old " petrol will restore its octane rating , but have never tried it myself. I think I would prefer to use the old fuel for degreasing etc , and run my motor on fresh fuel.

Ross

Ross is right...the volatile elements evaporate away leaving the less combustable and more importantly dirty burning elements behind.

Topping up with premium gives you premium with a higher ratio of nasties. It should be avoided if possible. The main danger comes at higher rpm's so if you have to do it keep the revs down.

Mercury suggest fuel is off by 3 weeks.

Cheers

Chris

[wildfish]

my mate splashed some fuel on a fire when we were younger! and it went off!

sorry fella!

[abiasin]

on the topic of fuel, is there any benefit or downside to using premium over regular unleaded in a 2 stroke? may be a dumb question but i got no idea.

[Nolongeramember]

on the topic of fuel, is there any benefit or downside to using premium over regular unleaded in a 2 stroke? may be a dumb question but i got no idea.

Basically, pemium fuel has a higher octane rating than regular. Higher octane is needed to prevent engine damage due to detonation in high performace (high compression, high boost etc) engines.

In my opinion, unless the manufacurer specifies premium fuel its a waste of money.

[abiasin]

Basically, pemium fuel has a higher octane rating than regular. Higher octane is needed to prevent engine damage due to detonation in high performace (high compression, high boost etc) engines.

In my opinion, unless the manufacurer specifies premium fuel its a waste of money.

cheers mate that was my original train of thought but never really wondered if that was the case.

[Robbielites]

I believe high octane burns hotter also and can do damage if it is not specifically recommended.

Cheers.

robbie.

[dangles]

I believe high octane burns hotter also and can do damage if it is not specifically recommended.

Cheers.

robbie.

exactly, in my 4st bike it was getting hot in summer and really tinny like a 2 st. Changed to std ulp and was fine

[pelican]

Hi all,

I am newbie to boating and could not find how petrol goes off.

Can some explain please.

Also if I have some normal unleaded in the fuel tank ,does that go off? or is it once 2 stroke is mixed that it goes off. My motor has the 2 stroke directly injecting.

Can I just top up the petrol with some fresh stuff and it will be ok?

Thanks

Simon

Just drain it off and run it in the car. You don't get stranded in a car and in a bigger tank it will be more diluted. Dead fuel will kill motors. Modern ECU motors like direct injection expect a certain bang for the volume of petrol it injects and if it doesen't get it it pumps more in and you get soot / gum etc etc and different running temperatures. No sweetening of the mix additives will help as you don't know original fuels specs and adding fresh in my opinion just leaves you with a full tank of crap fuel with a little better octane than the original dead stuff. Fuel oxidises in air and gradually deteriorated. Fuel companies at different times of year do Summer and Winter blends according to climate temperature and use different additives. Try and use all fuel in under one month especially if stored anywhere with changes in temperature or sunlight. Never ever use ethanol fuels and make sure you have a water separating fuel filter.

Sour fuel will often burn longer on concrete than fresh as all the explosive volitiles have gone and you are left with the slower burning longer carbon chains rather than the lighter ones that go bang. These burn slower and usually leave gum or soot residue.

Try and always carry a secomnd small tank that is filled at a second servo or time so if you ever get a bad batch you have some backup.

Direct injection motors have one advantage in that with a totally closed fuel system no oxygen exists and no sunlight so if your motor is stored on a constant cool temperature the fuel will remain OK for a reasonable time for storage rather than fractionalise / seperate oxidise , evaporate and leave gume and minerals.

Carbon Guard is a product that is a fuel stabaliser that will enable fuel to hold it's octane longer , prevent oxidation and store better and in Canada is what they mix with fuel in boats as a winterisation process where they aren't used for several months.

Pel

[jrzila]

Thanks for all your replies and very detailed explanations.

I think its case of better safe than sorry when you are on the water.

Now I have to figure out how to syphon the fuel out without copping a mouthful of below par petrol.

Cheers

Simon

[pelican]

Thanks for all your replies and very detailed explanations.

I think its case of better safe than sorry when you are on the water.

Now I have to figure out how to syphon the fuel out without copping a mouthful of below par petrol.

Cheers

Simon

Just use a jiggler siphon down the filler or use fuel bulb and just disconnect it from the motor end and extend it below the level of your tank- slow but will drain it down to fuel pick up level- then flush a bit of fresh through just to be sure is the fuel is really bad. Make sure all your clamps are done back up when done .

Try and inspect the tank when empty to see if there is sludge or water still in there so you know what you are starting with. It will also show you how much fuel in the tank us not useable as it can't be picked up by the motor.

Pel

Edited July 27, 2007 by pelican

[Penguin]

Now I have to figure out how to syphon the fuel out without copping a mouthful of below par petrol.

Cheers

Simon

If u have an air compressor handy u can put a piece of garden hose or similar into the bottom of

ur fuel tank, then get ur air line with a blower attached and blow air into ur tank.Place a rag

around the hoses to limit lost air pressure, and make sure ur hose end is going into a jerry can

or similar to capture the escaping fuel.Air goes into the tank and pushes out the bad fuel.This

method works very quickly.

penguin

Edited July 29, 2007 by penguin

[KingsRule]

Might just as a question in here insted of making a new post.

I have a spare 5l jerry can that we carry with us when we are out, its pre mixed with 2stroke oil and i think its been in there for about 2 or 3 months now, my question is how long will it last like that, or should i replace the contents now.

Rob

[Flightmanager]

I would think it is OK , but I would use it very soon. I have used 2 month old fuel/oil mix before , with no bad effects.

Ross