Stihl Motomix vs Trufuel 50:1

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I've seen reasonably intelligent people pull on start ropes until either the rope/recoil system broke or the injured themselves. A couple years ago I got a phone call from a woman friend asking me if I'd look at a mower they had that wouldn't start. Her husband had pulled on it so much that he suffered a fairly serious shoulder injury. He ended up going to emergency and wound up with his arm in a sling and a subsequent appointment for surgery on the arm.

I'm laughing just thinking about this. After the wife called me, she put her husband on the phone so that I could ask him a few questions. He starts talking like he knows what he doing... "Yeah good spark, lots of fuel, just won't fire." That had me scratching my head. I told him I'd be right over.

I pulled the spark plug and he's right. Lots of spark. I then said to the guy "I thought you said it was getting gas?" "It is." He said. "The spark plug is wet." I said "The plug is wet with condensation from you using the engine as an air compressor. That's water on the plug not gas." I traced the fuel problem back to blockage in the tank. Fixed that and fired the machine up in five or so pulls.

Now for the good part....

This fellow tells me that in his younger years, he was formally trained to be a light aircraft mechanic!!! Needless to say, I, personally am glad that he chose to change his vocation.
 
Funny story, it's good to hear stuff like this from other folks.. Sometimes I think I'm just to cynical (in fact my tag line on another forum is "Eternal Cynic") and oft have little patience and understanding for stupidness...
I suppose we are the types that figure stuff out and just fix it rather then the type to scratch our heads and call for help..
wink.gif


I have hurt myself pretty bad though trying to start an Engine on a spray rig that had a sheered flywheel key.. I didn't know it at first of course but it pulled/kicked back so badly that it yanked the handle from my hand and messed me up for months..

Edit to add:
I'm also glad never to have flown on a Plane that gent worked on..
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it could be the same stuff cause stihl changed the ultra to a red oil a couple months ago according to the dealer
 
That motomix is been out for some time now and still hard to find around here,i was told during our "stihl days" at my local JD dealer they do indeed use there HP syn oil in this product witch is a quality oil to begin with. I picked up two cans(good price) to try in my recent new SM311 the saw screams and runs awesome with this mix i love the no ethanol and 92 octane as Stihl recommends 89 minimum.

little pricey for the guy who uses his equipment on a regular bases and probably not practical but for the occasional user this is a good product IMO and the two year shelf life is a plus too.
 
I'm trying to figure out how to photograph it, because the trufuel 40:1 I bought isnt's red OR green, it's almost clear with barely any tint to it, no way they use stihl HP ultra in this stuff, it's nowhere near as green as the motomix 50:1.

I'm not even sure the bottle I got has oil mixed into it. it was $3.97 at Walmart, dented like it had been thru a warzone and last can on the shelf. It still smells like trufuel, but it doesnt look anything like the 50:1. I'm considering letting a sample boil off to see how much oil is left behind.

The trufuel MSDS states 50:1 is red, 40:1 is green, and "trufuel and purefuel" is clear.
 
We see a lot of water in customer's gas simply because of the high humidity we have here in the PNW. Every time it rains it's 100% humidity, and it rains a lot around here. The alcohol will draw water right from the air and into the gas, whether the gas is in the machine or in the can. If it reaches the saturation point, it will cause something called phase separation, and that can/will cause lubrication issues. In two-stroke engines, the water-ethanol phase will prevent some of the blended oil from bonding to the metal engine parts. The engine may not have enough lubrication, and engine damage will result.

Different fuels make a big difference in how an engine runs. Years ago I was priveledged to see a high speed camera set up in the top of a chain saw engine that really opened my eyes to this fact. They had several diff fuels they would introduce to the combustion and then show us the different combustion blooms that were produced by the diff fuels. The cheaper fuels made a much smaller, more irregular shape than the higher priced fuels, and produced much less power as well. That was at one of the Stihl service schools I went to, and I've been trying to get them to put it on video, maybe they will someday.

Boraticus, I can understand how you feel about those with seemingly zero mechanical ability, but I doubt you're an expert in IT, dentistry, brick-laying, etc. My brother has his Piled Higher and Deeper in computer science, but he couldn't change his own oil if you paid him $100. The way I see it, everyone has something they're good at, and bad at.
 
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Boraticus, I can understand how you feel about those with seemingly zero mechanical ability, but I doubt you're an expert in IT"

I may not be an expert but I know for sure that water will not enter a tightly sealed plastic gas container, which you happen to claim it does in the following quote:

"The alcohol will draw water right from the air and into the gas, whether the gas is in the machine or in the can."

If I'm incorrect, by all means, please tell us how moisture can permeate 1/8" thick plastic to contaminate the fuel??? I'd be interested to understand the physics of such a feat.

It would appear that I'm not the only one who's not an expert.
 
Originally Posted By: boraticus
If I'm incorrect, by all means, please tell us how moisture can permeate 1/8" thick plastic to contaminate the fuel??? I'd be interested to understand the physics of such a feat.


It's not nearly as difficult to understand as you make it out to be.

The gas can contains liquid fuel and atmospheric air. Every time you open it, fresh air enters the gas can. Every time you pour off fuel, atmospheric air enters the can to displace the liquid volume dispensed. Even when it's 'sealed' some minute amount of air exchange takes place - especially with plastic jerry cans in an outdoor shed. The large temperature swings & direct sunlight if outside can cause differential growth, not to mention greatly raise the internal pressure during the day (causing it to vent fumes) and lower it significantly at night (which makes it suck in fresh air).

Over time, this can cause the very hygroscopic ethanol (azetrope) fraction of gasoline to suck water out of the trapped air in the jerry can. Unless you're storing fuel in ziploc bags, it happens.
 
Originally Posted By: car54
I'm trying to figure out how to photograph it, because the trufuel 40:1 I bought isnt's red OR green, it's almost clear with barely any tint to it, no way they use stihl HP ultra in this stuff, it's nowhere near as green as the motomix 50:1.


Photograph it outdoors on a cloudy day (strong but diffused light) with a bright white background behind your Erlenmeyer flasks - sheet of paper or (clean) white t-shirt perhaps. That should help show the color differences better.
 
I already used all the motomix and 50:1 trufuel.

That's what I was getting at. I have a photo box to shoot in. but it's all gone at this point. =(
 
Originally Posted By: scurvy
Originally Posted By: boraticus
If I'm incorrect, by all means, please tell us how moisture can permeate 1/8" thick plastic to contaminate the fuel??? I'd be interested to understand the physics of such a feat.


It's not nearly as difficult to understand as you make it out to be.

The gas can contains liquid fuel and atmospheric air. Every time you open it, fresh air enters the gas can. Every time you pour off fuel, atmospheric air enters the can to displace the liquid volume dispensed. Even when it's 'sealed' some minute amount of air exchange takes place - especially with plastic jerry cans in an outdoor shed. The large temperature swings & direct sunlight if outside can cause differential growth, not to mention greatly raise the internal pressure during the day (causing it to vent fumes) and lower it significantly at night (which makes it suck in fresh air).

Over time, this can cause the very hygroscopic ethanol (azetrope) fraction of gasoline to suck water out of the trapped air in the jerry can. Unless you're storing fuel in ziploc bags, it happens.


The volume of air and durations of time involved in brief exposures as you've outlined will not contribute significantly to water absorption. In reality, under those conditions, it would be miniscule. I swear, by the way some people talk, you'd think Niagara Falls pours into the fuel can ever time we take the cap off.

When I leave fuel cans for six months at a time, the cap is secured tightly. I never get moisture via "osmosis" through the container.

I have friends who fly plastic drums of avgas and regular pump gas up to the Arctic for future flights and activities. They cache their fuel in very remote strategic locations for sometimes up to a year. Strangely enough, they never have problems with moisture absorption either.

Careless fuel management may contribute to moisture absorption. From my many years of experience, and the experience of others I know, careful fuel management will virtually eliminate it.

There's no need to purchase $7.00 per liter for ethanol free fuel if people manage their fuel storage properly. None whatsoever.
 
Something else to consider is that it's not about the ratio of water to 5gal of fuel, but the water is heaver and will only see your piece of equipment at the end of your fuel stock. By that point the fuel:water ratio could be as high as... well very high.
 
Originally Posted By: boraticus
"
Boraticus, I can understand how you feel about those with seemingly zero mechanical ability, but I doubt you're an expert in IT"

I may not be an expert but I know for sure that water will not enter a tightly sealed plastic gas container, which you happen to claim it does in the following quote:

"The alcohol will draw water right from the air and into the gas, whether the gas is in the machine or in the can."

If I'm incorrect, by all means, please tell us how moisture can permeate 1/8" thick plastic to contaminate the fuel??? I'd be interested to understand the physics of such a feat.

It would appear that I'm not the only one who's not an expert.


Wrong. High Density Polyethylene (HDPE), which is what most gas can/tanks are make of, is permeable to both water vapor and oxygen. It takes time for water vapor or O2 to migrate through, but it definitely happens. In fact most plastics are relatively permeable unless they've had a layer of aluminum or other metal deposited with vacuum vapor deposition. That's why plastic food packaging (potato chips, MREs, juice pouches, etc) have a shiny aluminum layer if you look at them.

So, while you don't think water vapor can migrate through plastic, I assure you it can, certainly over a period of a month or more in a high humidity environment. Temperature will accelerate this btw.

Also, as the other poster mentioned, there is the air in the container to consider. Certainly in a half full container opened in a humid environment there is a decent amount of water vapor in the container.
 
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Can you guys provide some facts (data) that shows:

1. That moisture can migrate through plastic enough to cause a problem with things like gasoline or brake fluid.

2. That atmospheric moisture (not rain or condensation, but vapor/humidity)could be absorbed in enough quantity to cause problems in gasoline.

I searched, but only found one old 1995 document that refutes #2, but I haven't taken the time to access it's accuracy.
 
here is the trufuel 40:1 I picked up at walmart for $3.97. Appears slightly green against white.

motomix3.jpg
 
Originally Posted By: doitmyself
Can you guys provide some facts (data) that shows:

1. That moisture can migrate through plastic enough to cause a problem with things like gasoline or brake fluid.

2. That atmospheric moisture (not rain or condensation, but vapor/humidity)could be absorbed in enough quantity to cause problems in gasoline.

I searched, but only found one old 1995 document that refutes #2, but I haven't taken the time to access it's accuracy.


Here's a document that shows the gas permeability of common plastics.

http://www.dynalabcorp.com/files/Use and Care of Plastics.pdf

They don't show H2O permeability but they do show O2, CO2, and N2. They show water absorption, but that is not the same as permeability. HDPE is sort of a middle of the road plastic in terms of permeability, better than LDPE, not as good a PFA or Acrylic, but still relatively permeable, particularly to CO2 and O2. I've see engineering handbooks that listed the H2O permeability of HDPE and it was about 90% of the O2 permeability if I recall.

HDPE is commonly used in fuel tanks for cars, however in this application the tank is typically refilled often enough that it is not an issue. For fuel storage tanks (portable gas cans for example) there is an issue for long term storage (think months). It's not a huge issue and it may not even be the dominate issue in many cases (particularly if the gas can is half full, in that case the moisture in the air space is probably a bigger problem). However, the point is that plastics are not perfect barriers against oxygen and water vapor (both of which degrade fuel). Metal is a much better barrier (in fact a metal can is almost completely impermeable), but you have issues with corrosion. Plastics are a good compromise as there are no corrosion problems, but fuel will deteriorate somewhat more quickly in a plastic container compared to a well sealed metal container.

Lastly, it matters what is being stored in these plastics. Ethanol is hygroscopic, as are most brake fluids. Which is more hygroscopic I couldn't tell you, but obviously more hygroscopic fluids will have bigger issues. In a brake system moisture will invade via the master and wheel cylinder seals, as well as though the plastic brake reservoir. Which of those two paths are dominate I couldn't tell you.
 
"Wrong. High Density Polyethylene (HDPE), which is what most gas can/tanks are make of, is permeable to both water vapor and oxygen. It takes time for water vapor or O2 to migrate through, but it definitely happens."

How many million years will it take for one cup of water to infiltrate a five gallon fuel container if tightly sealed?

The ethanol water absorption hysteria is wildly exaggerated. A person is more likely to suffer from the effects of contaminated fuel when filling their container at the pump.
 
Most water issues are caused by the breeze blowing through the vents of you tank and carb itself.
but picture this. ten drops of water from the last splash of your fuel makes it into your mower and you store it for 6months with those ten drops in the bole. the coating and the bole is corroded but the water in one little spot and rust starts. you go to use the unit later and it starts and sputters for a bit until fresh fuel reaches the bole. later a small piece of rust flakes of in the bole and clogs the main or pilot.
Tiny bit of water= no lawnmower. It doesn't take but a tiny bit to be an issue.
 
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