Pre-mix gas or not to pre-mix gas

[brianvolt7]

1990 Force 120

I have always pre-mixed my fuel 5 gallons at a time and then filled the boat. It takes about 20 gallons.

Recently, and for the first time, I poured the oil into the tank then filled the boat at the pump. I experienced some dramatic performance deficiencies with the motor.

Does anybody have an opinion on pre-mix vs. mix at the pump?

 

[Silvertip]

Re: Pre-mix gas or not to pre-mix gas

Any performance difference you noted was due to something other than premixing. It makes no difference which way you do it. Current outboard oil does not need to be shaken vigorously to mix properly. By the time you leave the gas station the boat has moved enough to properly mix the oil. As with mixing in a separate container, you do need to properly measure the mix (1 pint to six gallons). If you know the tank will hold at least 12 gallons, pour in a quart of oil and add the fuel. If you have a large tank and know it will take at least another 6 or 12 gallons, repeat the process by adding another pint (for six more gallons or a quart for another 12). As you approach the full point, cut the measure in half (1/2 pint for 3 gallons). If you can't squeeze in the 3 gallons -- no big deal. The mixture will be only very slightly rich on oil and the engine won't care.

 

[Philster]

Re: Pre-mix gas or not to pre-mix gas

Someone might say that the oil went straight to the tank's pick up, and that you should probably add the fuel first, then the oil to prevent this.

I did just that for years: Add half the fuel, then half the oil, then half the fuel, then half the oil.

 

[dingbat]

Re: Pre-mix gas or not to pre-mix gas

And they wonder why I leave my oil injection hooked up Low on oil, fill it up. Low on gas, fill it up.

As noted above, modern outboard oils mix on contact. I mix 5 gallons at a time for the golf cart. Oil then gas, gas then oil. It's doesnt matter one way or the other. It's completly mixed by the time I pour it in the tank.

 

[hawkman-1]

Re: Pre-mix gas or not to pre-mix gas

I fill the tank then add the right amount of oil. I have a few gallons of mix in a can and use a little to wash the oil into the tank from the filler neck. The ride to the ramp mixes it just fine.

 

[Chris1956]

Re: Pre-mix gas or not to pre-mix gas

Silvertip has put it most succintly. If there is mixed fuel in the tank, add the oil and then the gasoline. It will mix before you are able to pay the man for the fuel. If the tank is dry, it will take a bit more time to mix, like until you pull away from the pump.

 

[brianvolt7]

Re: Pre-mix gas or not to pre-mix gas

Thanks all! I will start to look elsewhere for the cause of the perfomance issue.

 

[rodbolt]

Re: Pre-mix gas or not to pre-mix gas

I must respectfully disagree.
did one recently.
customer had the OMS pumps removed from his twin 225 OMC's.
they dumped in 4 gallons of oil added 100 gallons of gas. one engine had just been replaced and the oil was doubled for breakin.
they made it about 100 yards when the engines quit.
once I drained the pure oil from the carbs they both ran on the shop tank.
I used my electril pump and let the fuel recirculate for a few hours and all was well.
but that oil sat like a turd in a bowl for quite a while before mixing.

 

[brianvolt7]

Re: Pre-mix gas or not to pre-mix gas

I think the next tank I will pre-mix again.

After not pre-mixing the motor smoked bad on start up and idle. WOT was the same but I could not troll at all, it would just die.

Once I pre-mix and take it to the lake I will post the results.

 

[kenmyfam]

Re: Pre-mix gas or not to pre-mix gas

Was the 4 gallons of oil put directly in to an empty tank ???

 

[Silvertip]

Re: Pre-mix gas or not to pre-mix gas

If you feel you must agitate the mixture, simply "rock the boat" while filling. Most rigs can be pushed side to side quite easily. Try it.

 

[Fed]

Re: Pre-mix gas or not to pre-mix gas

With an OMC VRO you're supposed to run premix until the VRO injection is varified by usage which means running at 25:1 for the test.
I was in this position but forgot to add the oil until the cook reminded me after the motor was warmed up at the dock.
I poured 1 litre of oil into the 50 litres of gas in the tank, took off and got 100 metres or so before the motor died completely.
It took a lot of rocking, coughing & spluttering before it finally came good and it was right from then on.
One thing it does show is the oil is heavier than gas and goes straight to the bottom of the tank.
I've been told that to comply with TCW3 specs the oil must fully mix with 10 inversions or so, I should google that to confirm it.
If I had to fill at a dock I'd be trying to mix it a bit by adding oil then gas then oil then gas etc, as well as rocking the boat after it was full. I think towing a few miles from a garage 'probably' works too.

 

[Chris1956]

Re: Pre-mix gas or not to pre-mix gas

Rodbolt has described an extreme example. If you pour a pint of oil into an empty 6 gal can and fill with gas, it will mix immediately.

If Rodbolt's customer had added 1 gal of oil, every 25 gal of gas or so, it would have also mixed fine.

 

[d.boat]

Re: Pre-mix gas or not to pre-mix gas

I always used a funnel to fill my tanks so that I could pour the oil into the funnel while the gas was pumping into the funnel. I never had a problem. I use VRO/OMS now, but last weekend I had to put oil into one of my built-in tanks that had about 24 gallons of unmixed gas in it already. (for the kicker ... long story....). I had a wooden stick on board and just stirred/agitated the gas as much as I could while I gradually poured in the oil and it seemed to work fine.

 

[MikePNJ]

Re: Pre-mix gas or not to pre-mix gas

I seem to be having an issue with premixing I think.

Just boat the boat a a month ago. It has a yamaha 115 2 stoke outboard and I filled the tank before bringing it to my slip. (half full gas tank added 15 more gallons of gas then the oil) drove to the dock dropped it in and it ran horrible, bogged out after idle speed, smoked some.

I had both carbs rebuilt and all was fine. Ran it a few days.

Time to refuel, 30 gallon tank. I added 25 gallons of gas at the dock, poured in 2 quarts of TCM-3 oil after fueling via funnel. Left the no wake zone and dies after passing idle speeds, smoked and not running good. Brought it back to the dock.

Get in it the very next day ... started up fine and ran well the next 3 times out.

Wondering if it is the fuel & oil not mixing well.

Time to fuel up soon, so I don't want the issues if it can be avoided.

Any thoughts???


Mike

 

[d.boat]

Re: Pre-mix gas or not to pre-mix gas

Just put the oil in before the gas, or while you're gassing and the agitation of filling the tank will mix it up.

 

[rodbolt]

Re: Pre-mix gas or not to pre-mix gas

and thats why manufactures have spent so much money on oil injection methods.
mixing 6 gallons for your antique 6hp jonnyrude is a bit different than mixing 100-150+ gallons for the 26 grady with twins.
in my area if its got a portable tank odds are high its running on my shop tank.
the preferred method is to mix the oil and gas in a seperate tank then add it to the boat tank.
however yall do as ya wish, makes customers .