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Old 06 June 2015, 18:46   #1
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Old fuel in tank/motor...what to do?

Hey all,

So summer's just about here and I think I screwed up on not winterizing my motor correctly. I have a 4 stroke Mercury 45 with EFI. The gas in the tank and probably some in the engine is about 7.5 months old. I never got around to putting any stabilizer in it and can only assume there is some ethanol.

I ran it about 3 months ago in my driveway for a little bit to keep things flowing. I was just about to do it again and got to thinking about the gas. After doing some research it looks like the gas is probably bad and that I shouldn't run it. I'm considering ditching the gas in the tank and checking out the fuel filter. Is there anything else I can or should do to drain bad fuel from the motor? Or, anything else I can do in general to get her ready for the summer?
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Old 06 June 2015, 19:05   #2
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Iv always been sceptical about the life of fuel. Unless it had been years old or had water in it i never had a problem. My zapcat never had stabiliser in it and hadn't been run in 8 months. Started second pull and ran as fast as ever so unless it had issues I wouldn't worry personally
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Old 07 June 2015, 03:17   #3
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I usually just top off the tank with fresh and run mine, a few months and all should be well, I've a water separator in case condensation has got in.

If I have one of the two tanks empty I'll start her on the new, run her on the old and run down on the new.

T
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Old 07 June 2015, 03:24   #4
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1eyedjim the OP is in the states where they like to dilute their petrol with alcohol. The alcohol absorbs water from the air (poly you have better things to do than correct the science...) Then cheekily evaporates off leaving water in your fuel.

We have far less alcohol in our fuel this side if the pond... We prefer to drink it!

But there are huge variables that play into all this: air space in tank, sealed or open to air, temp & humidity in storage and when filled. All of that again in the 'gas' station tank.

If its a portable tank I'd empty it into a jerry can and start the season with fresh. Take a look at the filter by all means. If she's running good I'd be tempted to mix my old in in small quantities...

But the purists will have a fit. Mind you I filled a diesel with petrol and realised after 10litres added another 35 of deisel on top and got away with it...
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Old 07 June 2015, 03:51   #5
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Originally Posted by ShinyShoe View Post
But the purists will have a fit. Mind you I filled a diesel with petrol and realised after 10litres added another 35 of deisel on top and got away with it...
That seems a little drastic to deal with water in the fuel?

OP - I'm guessing that you have a portable tank for your 40hp? And gas costs like "nothing" a gallon?
Your engine (if I understand correctly) has fuel injectors? I do know that certain injectors can be averse to getting water in them - not sure about yours. The water that "may have" mixed with the fuel would be bound with the alleged ethanol and thus will not drop out in the filter but continue to the injectors. If I was in your shoes, I'd just change the fuel out and make a note to use stabiliser in future.
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Old 07 June 2015, 04:01   #6
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If in any doubt - and you are or you wouldn't be asking - dump the old & replace with new.
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Old 07 June 2015, 10:09   #7
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Thanks All. I am/was probably overly concerned about this but figured it couldn't hurt to play it safe since I normally learn all my lessons the hard way! I'm just going to ditch the old fuel, check the filter, and fire her up.

As to the stabilizers, do you just add it to whatever fuel you have sitting in the tank before an extended idle period or must you run that fuel through the engine as well?
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Old 07 June 2015, 15:59   #8
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Follow the instructions with whatever brand you decide to use.
An example here:
STA-BILŽ Brand Fuel Stabilizer for Gasoline-Powered Equipment
"USAGE DIRECTIONS:
1 oz. (30mL) treats up to 2˝ gallons (9.5L) of fuel. Use STA-BILŽ only with FRESH FUEL, and keep gas can or tank 95% full to avoid condensation build up in tank during storage. Run Engine for 5 minutes after adding product to treat entire fuel system. Product does not contain alcohol."
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