Oil mix question

[davefrommd]

I bought this brand new mcculloch pm10-10s chainsaw and the front of the owners manual sais 4oz oil to 1 gallon of gas (mcculloch custom lubricant) and In the back of the manual it sais 40-1 mix 3.2oz. per gallon of gas. Which one should I use or which is better.  Thanks in advance.  Dave

[Kevin]

3 oz. of oil with one U.S gallon of fuel will give you 40:1
4 oz. of oil with one U.S gallon of fuel will give you 32:1

I would give a new saw a little more oil for the break-in.
If they say it's 40:1,  I would give it 3.5 or 4 oz. of oil for the first few tanks.
Might be a little smokey but good for the saw.
If it isn't smoking with 3.5 oz. of oil that's what I would continue to mix after the break in.

[davefrommd]

Hey thanks kevin, I think I got all my chain saw business taken care of. This forum was a great help. Dave

[Kevin]

Have fun with your new saw Dave, look after it and it will serve you well and last a long time.

[MrMoo]

I once had a guy at a power equipment place tell me to always run 32:1 mix no matter what the manual says. He said it might be smokey but it will be better for the engine.
I have always run my Husky that way with no problems.

[IndyIan]

Another question about pre mix;

I believe the recommended way to mix is to add some gas to the oil and then dump that into the gas can.  Anyone actually do this?  
I imagine there is some molecular interactions to do with surface tensions, etc, that make this the better way to mix oil and gas but I can't remember my chemistry that well

I always measure the oil in a measuring cup and dump it straight into the can then rinse the cup out with gas.  
It amazed me how much the oil resists mixing with the gas, usually I fill and swirl twice and there is still a bit of oil stuck to the sides of the cup.  I use husky oil if that matters.

I now shake the heck out of the gas can before I fill my saw but I still wonder if some of the oil never really mixes into the gas.  I guess its another reason in my mind to go with 40 to 1 instead of 50:1

Ian  

[davefrommd]

Thanks everyone for your input on the oil mix. I now know what I'm doing a little more then before. Dave

[Mark M]

Hi Ian

It sounds like you are doing a good job of mixing your gas. By rinsing your oil cup you are getting what us chemists call a "quantitative" transfer, which is a fancy way of saying you are getting all the oil into the gas. ;)

I always put a little gas in the can then dump in the oil and swirl and shake it up as well as I can without putting on the lid (I'm a little lazy). Doing it this way there is room for the gas and oil to slosh around a lot and mix together. Also the oil doesn't stick to the can (as you observed) when you dump it into the gas instead of an empty can. I put in a little more gas, shake, and then repeat the process a couple of times. It's important to leave a little space in the gas can (which is called "ullage") so the mixture can slosh around and mix completely. Finally I put the lid on and shake until I get tired of shaking (which isn't very long).

I once had a discussion with a former chemistry teacher of mine about whether oil and gasoline formed a solution or a mixture. According to the textbooks: a solution is a homogenous mixture that contains only one phase and it has uniform properties throughout. No matter where we take a sample from a solution, we will obtain material with the same composition as that of any other sample from the same solution. Solutions such as vinegar in water do not separate by normal sedimentation or filtration.

By contrast, a mixture, or more properly a heterogeneous mixture, contains visibly different parts or phases, each of which has different properties. Immiscible liquid-in-liquid mixtures (such as water and salad oil) do not dissolve in each other and can be separated by settling or filtration. This is why it is necessary to shake some salad dressings

Since oil and gasoline are miscible, which means they dissolve in any amount in each other, it stands to reason that they form solutions, and solutions do not separate. To make a long story short – I asked him if he shakes his gas can before filling his chain saw and he said he did. I asked him why since if it was a solution it should not separate. He said something to the affect that most people who write chemistry textbooks probably don't have chain saws. ;D

Mark

[Tom]

Thanks Mark.  That was fun reading.  I don't shake my chainsaw gas deliberatly.  I have wondered if the evaporation of the gas left a denser mixture at the top or bottom of the can. Because of the difference in volativity, perhaps oil and gas form more of a mixture than a solution. :-/  

That would make a pretty good high school experiment.    :D

Does a fly land on the ceiling in a half loop or a half roll?

[Minnesota_boy]

When you swat that fly on the ceiling, does he land feet first in your coffee and then roll over or does he naturally land on his back?

The quality of the oil may be more important than the mixture.  I've seen the exhaust ports nearly plugged with deposits from someone using cheap oil.  I use a good oil, but not necessarily that sold by the dealer.  I have enough different 2-cycle engines that I can't afford a seperate can of fuel for each brand.

[Mark M]

I'll have to think about that fly a little.

I once heard that if you try to catch them you should slide you hand up behind them because when they take off they move backwards a little. I usually just use my tongue :D

I tink a denser liquid would sink to da bot-um of da can.

The volatility does pose an interesting question though Tom. Since the gasoline is more volatile it will evaporate more readily than the oil so it is possible that a concentration gradient could exist if the can sat undisturbed. This may be the reason the manufacture says to shake the can before filling the saw. Me myself - I am usually so happy when I get to cut wood that I usually skip all the way to the wood pile and my gas gets a good shaking. :D

Mark