Converting to pre mix , unsure of amount of fuel in tank

[Blake0912]

I'm going to by pass the oil side of my VRO this weekend and convert to pre mix on my 87' 225 Johnson , but I'm not sure how much fuel I have in my tank the guage is almost on E but I have a 70 gal tank I'm assuming it's about 15 gallons.
My question is if I add about 40 gallons and mix it 50:1 , then add the extra oil for what's already in the tank ( I'll add enough for 20 gal to be safe) do you think I would be alright , or should I go threw the trouble of draining the tank to be 100% sure how much fuel I have ?

Thank you

 

[Home Cookin']

Re: Converting to pre mix , unsure of amount of fuel in tank

The easy solution occurred to me after writing the more complicated: dump in oil for 70 gallons and fill it up. Done.


I would never rely on a boat fuel guage. You could stick a ruler down in the tank, check the depth and compare to the overall depth of the tank, and do the math (assuming it's rectangular; some are shaped oddly toward the bow to fit.)

The 50:1 mix does not have to be precise to the drop, so I don't see anything wrong with estimating and err on the side of more oil. Even if you added 55 gallons of premix to 15 gallons of unmixed you'd be OK.

This may be a good opportunity since you are almost empty to drain the existing gas, inspect it, clean the tank, and put it back in with fresh gas + oil.

 

[Blake0912]

Re: Converting to pre mix , unsure of amount of fuel in tank

Thanks that some good advise I never thought of just filling it up all the way lol. I just have always assumed its a 70 gal but I've never topped it off, ill definatly use a ruler ( thats my 13fts whalers trusty gas guage , has never let me down) to get a better idea i usually dont trust the guage either it will say E then plane up and it has 1/2 tank. Happen to know what size gas tanks pursuit used in '87 on there 21ft CC?

I may just pump it out to inspect the tank , but my filters / water seperators have always been clean and the gas is only a few weeks old with stabile in it.

 

[renelson]

Re: Converting to pre mix , unsure of amount of fuel in tank

If you want to be sure, siphon the gas into a clean container and measure the volume (like in a 5 gallon bucket). If it is new gas, just funnel it back into the tank and fill the tank up, adding the volumes together. Just make sure to use a clean hose for siphoning.

 

[Home Cookin']

Re: Converting to pre mix , unsure of amount of fuel in tank

remove the deck plate above the sending unit; there should be a plate on the tank with the capacity. Otherwise you have to go with the owner's manual. Or drain it completely, and top it off to nkow capacity.

Hint: when filling, add oil first (and stabil) and then gas; do it in installments. otherwise you may top it off and not have room for the oil.