Determining oil % in an mixed fuel gallon

[Dennis Toth]

Guys,
Been working through some fuel that has been in the shop for a few months. I have been doing a lot of traveling so haven't paid attention to what fuel can has extra oil and which one is just stock SIG Champion 5%. I had some fuel that had extra oil to get it to 28% with 15 % nitro and a new gallon of 5% which I blended to get the nitro to around 7%. Being away as I burned off some of the mix I just started adding new fuel to the same jug and not thinking about the oil %. I have noticed that my engine run is a little longer then in the past and a little leaner. Seem I might be a little low on oil for the Fox 35.

I want to check the %, the way I plan to do this is to measure out a sample (4 oz is the size graduated beaker I have), pour into a wide bowl and put it in the sun for the day. I hope this will evaporate all the light stuff leaving the oil which I can then pour back into the beaker and see the volume left then calc the %. Am I missing anything with this plan?

Best,     DennisT

[frank mccune]

    Hi Dennis:

    Your method is the one that I used to determine the oil percentage in a can of questionable fuel.  Not being very smart or sophisticated, that was the only way that I could come up with to solve the problem.  The wind also aided in removing the alcohol from the mix.  It answered the question as to why my engine's p&c were ruined after about 40 seconds of running time! Almost No oil!

     MM Yes, I too have seen Fox 35 Stunts run and raced on very little oil.  Did it damage the engines, I do not know as there owners claimed that there was no damage. I doubt that anybody did a scientific test with a Fox 35 running on fuels of varying oils and oil percentages. If was ever done, I would like the read the results.  I did hear of a test Duke did on one by hooking an engine up to a 55 gallon drum of fuel and allowing it to run non stop for a very long period of time. It was printed somewhere but if I remember correctly, that was all that was mentioned. Incentive for a research paper?

                                                                                                           All of the best,

                                                                                                           Frank McCune

[peabody]

Den....
Why not just leave it in the beaker?

[Steve Hines]

More nitro less time

[bill bischoff]

Large shallow dish= more surface area= faster evaporation of volatiles. Perhaps not laboratory grade accuracy, but good enough for comparative purposes. An 8 oz sample should large enough to keep errors small. I say why not? Give it a go!

Of course you said leaner and longer run time. These go together. A richer setting will not run as long. Have you tried a simple twist of the needle?

[Dennis Toth]

OK, just brought the sample inside and dumped it back into the beaker, looks like there is 25% oil left. Think I might add a little to get to 27% to carry a little more heat out of the engine.

Best,    DennisT

[Larry Renger]

Also, I wouldn't trust that test to get it down to 100% oil, bet there are some other fuel constituents left.
I would hit it with a heat gun and see what I can drive off!

[frank williams]

I also use this method to check fuel oil content.  I pour up 100 ml from a graduated flask into a Fritos bean dip can.  Empty can preferred.  I put it on a coffee warmer that will heat it to 100+ degrees.  This is faster than natural evaporation and , like Larry says, it probably drives out more of the volatile constituents.  I usually do the test a couple of times to make sure I'm getting the same answer.  I've also used the flame method.  This is where you set the fuel in the bean dip can on fire.  This works well sometimes with the fire going out by itself leaving only the oil.  However, sometimes the oil will sometimes continue to burn if its not all castor oil.

[Doug Moisuk]

I had some question about one gallon I have. Engine was erratic. So I did this test. Compared it to another gallon.

[frank mccune]

          Hi Ty:

          Yes, I did! The last gallon that I mixed I inadvertently doubled the amount of oil in the mix.  I determined this by the evaporation test as above.  I solved the problem by mixing a gallon of "fuel" sans oil and mixed the two together.  My engines would not start on 48% oil.

                                                                                                                        All of the best,

                                                                                                                        Frank McCune

 

                                                                                                                                         

[PaulGibeault]

Please tell us how you did your test!

I had some question about one gallon I have. Engine was erratic. So I did this test. Compared it to another gallon.

[Doug Moisuk]

I used the fuel in question and a second gallon I new was good. Filed the syringes to the 50 cc mark.  I then let them sit until the alcohol and nitro evaporate. Took over a week. I could have put the syringes in boiling water to speed up the evaperation. There is supposed to be 22% oil. So it looks pretty good but most important the are the same. So I didn’t mess up in the mixing of the gallon in question.

[phil c]

If you haven't already done this you should:  Mix up a gallon of fuel using volumes measured with a graduated cylinder, or at least a measuring cup.  Evaporate that and see how close the measured result is to what was put in.  It's called a control.  The stuff has to be at exactly the same temperature as when mixed, measured with a good thermometer to be accurate.

Temperature, Water picked up from the air, the nitromethane, and the fact that mixing liquids doesn't necessarily come up with the same volume as what you measured in.  Nitromethane and methanol mixtures are pretty sensitive to temperature.    See the second chart at http://www.turbofast.com.au/racefuel8.html  .    A 5-10degF change can make a 1-2% difference in apparent percentages.