filled up with diesel by mistake

[cobb3333]

Stupidly i put 22 ltrs of diesel in my fuel tank, i run a f115 four stroke. i was thinking of filling the tank with hi octane petrol to dilute it , the tank holds 130 ltrs. Would this work . Or will i have to empty the tank ,dispose of the fuel and start again. The engine has not been run since the fuel went in.

[99yam40]

I would remove all I could and flush the lines and filters with good fuel.
they do not mix and run well in a gas motor or a diesel motor

[boscoe99]

You gotta get it all out and then have the tank cleaned and the system purged of any contaminated gasoline. All the way to the fuel injectors if that is what it takes. Sounds like all you need to do is to dump the fuel and have the tank cleaned if you have not run the motor.

A small, small amount of diesel is all that it takes to destroy whatever octane the gasoline had. Without octane your motor is at great risk of being destroyed. The F115 has a fairly high compression ratio if it is not one of the most latest models then it does not have a knock sensor for self preservation.

We live and learn. Don't beat yourself up over it. It has happened before and will happen again. Unfortunately.

[bajakeith]

kerosine in tank

two ways to go...remove the anti-sipion valve on top of tank and replace with a brass barbed fitting w/two clamps and grease on the pink sending wire and drain tank........or try and run a hose down the fill hose...Pain in the b__

[cobb3333]

thanks for the input. I have picked up some fuel drums for the contaminated fuel . I will try and access the tank from the sender unit, it is most accessable.Hopefully i will learn from my mistake.

[bajakeith]

damn fast reply

Hi Im out in Monterey bay ca......LOL as log as your newer boat is not a POS "Scout" there should be a access cover

[zenoahphobic]

diesel

I would have thought that adding diesel to petrol would not be such a problem if in a small quantity. It would simply act as a lubricant, just like adding any other oil.
Of course if the fuel line has diesel in it the motor would not run so cleaning out the contaminated fuel is sensible. If the engine runs then the concentration is not high the negative affect would be carbonization on the head, valves and plug which would burn away in time with fresh fuel.
Not withstanding the above the engine would run lean which poses potential for damage by overheating.

[boscoe99]

I would have thought that adding diesel to petrol would not be such a problem if in a small quantity. It would simply act as a lubricant, just like adding any other oil.
Of course if the fuel line has diesel in it the motor would not run so cleaning out the contaminated fuel is sensible. If the engine runs then the concentration is not high the negative affect would be carbonization on the head, valves and plug which would burn away in time with fresh fuel.
Not withstanding the above the engine would run lean which poses potential for damage by overheating.

You would have thought wrong.

Octane is needed to prevent detonation. Detonation kills motors. Gasoline being contaminated with diesel will kill the octane rating.

[zenoahphobic]

You raised an interesting point. However Diesel will not burn in an spark ignition engine because the compression is not high enough. It however may burn after the petrol is ignited by the increase in pressure just as any other hydrocarbon would such as two stroke oil mixed in the petrol. Engine oils also have low octane rating and these only affect engine running by leaning of the fuel by dilution.
There are hydrocarbons that can be added in small quantities to raise octane. But you cannot reduce the octane rating significantly by adding the same amount of low octane additive.
This can easily be demonstrated by getting a container and adding a litre or two of clean water. Place a drop of food dye and see how it immediately colours. Now add another drop but this time of water, it makes no difference. Several litres of water (maybe many times the original quantity of water) is required to make the colour disappear!

[boscoe99]

If the fuel system was completely full of diesel then you are correct. The motor would not run at all. If it can not run then no damage will occur.

But that is not the situation. The OP has added about 5 gallons of diesel to a quantity of gasoline. I suspect that the mix is such that it will burn when ignited by the spark plugs. But the octane rating will now be so low that detonation might occur.

Yes, a two stroke motor has oil added to gasoline but those are low compression ratio motors. The OP's motor is a high compression ratio motor. The higher the compression ratio the more likely that detonation will occur. That is why race motors use gasoline with a high octane rating. The F115 is known to be susceptible to detonation even with the use on non-contaminated gasoline. So much so that Yamaha had to add a knock sensor to help protect the motor from being damaged.

Diesel is more or less the equivalent of jet fuel. In aviation a number of piston engines have been damaged when jet fuel was mistakenly added to the gasoline. People have died. The FAA mandated changes to the fuel tank openings in the gasoline fuel tanks (smaller opening) and changes to Jet A fuel nozzles (larger size) so that Jet A cannot be added to a gasoline tank. It was that big of a problem. Google it.

It does not take much diesel, or oil, to get into a gasoline fuel system to cause a problem. Worn piston rings have been known to allow a small amount of oil to get into the combustion chamber which caused detonation to destroy the motor.

[99yam40]

So adding diesel will cause the gas to burn faster, not slower?
This I did not know

[boscoe99]

How did faster/slower burn come up?

Detonation is not a burn. Detonation is an explosion.

[99yam40]

It was my understanding that higher octane rating meant slower burning fuel, lower octane rating meant faster burning.

My guess would be an explosion would be instantaneous burn of the fuel, very fast spread of the flame

But not sure now

[DennisG01]

It was my understanding that higher octane rating meant slower burning fuel, lower octane rating meant faster burning.

My guess would be an explosion would be instantaneous burn of the fuel, very fast spread of the flame

But not sure now

I see where you're coming from with "faster and slower", but those are misleading terms. Now, if I'm understanding things correctly, and can coherently relay my thoughts...

Lower octane will 'explode' earlier in the piston cycle - in other words, "pre-detonation". Rather than waiting for the spark to ignite the fuel/air mixture, the compression (which equals heat) created by the rising piston will cause some of the fuel to ignite before (pre) the full mixture. If you combine a higher compression engine with this lower octane, this problem will be even more evident. Higher octane will "resist" pre-detonation until the appropriate time. So your "faster" could be thought of as pre-detonation (exploding too early in the cycle) and "slower" as waiting until the appropriate time to explode.

[99yam40]

gas motors spark the plugs at different degrees before TDC,( before the piston reaches top dead center). This means it is burning before the piston reaches the top of the compression stroke.
If it burns too fast or is sparked to early it puts down force on the piston coming up and when it hits and rolls past TDC the piston skirt will slap the side of cylinder. this piston slap is what some called knock or clatter.
the spread of the flame depends on the location of the plug, shape of the combustion chamber , and the rate of burn of the fuel.
Some use plugs in center ,some from the side, some use more than one plug to get better spread of flame front. Timing of the spark is con*****ed many ways to keep this all under control. But the rate of burn has to be where they designed it to run on

Diesel motors I think compress the air and inject the fuel at the time they want it to burn.
I guess that is the only way to control when it goes off.( I really do not know)
I do know when you add other hydrocarbons in the air it compresses you get a run away. I have also read you also inject propane or butane with it to get the diesel to burn better and cleaner.

I guess you call the diesel a con*****ed explosion but not sure I would say the same on gasoline