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Fuel boiling

catbuster

catbuster

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Yes, as pressure decreases the temperature a liquid becomes vapor decreases, or vice versa. Water will boil at room temperature if you pull enough of a vacuum.

Or, if your tank vent is not working correctly allowing air into the tank the tank will be put under a vacuum and can boil at a very low temperature.
 
Wood Doctor

Wood Doctor

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This is an old thread. Is it possible that early versions of ethanol caused this? I have never seen boiling mixed fuel since operating chainsaws all the way back to 1977.
 
fossil

fossil

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An older gentleman (82 at the time) that started cutting in the early 50's mentioned boiling to me.

He started with an IEL DD (painfully slow)
Then MAC's (hated them as they often wouldn't start hot)
Switched to Pioneers (liked the saws but the clutch going ding ding ding at idle drove him nuts)
Switched to Homelite XL-902AM's (Liked them)
Bought a Super 650 , 43" barm to cut dead Elm's. Thought he's died and gone to heaven

Sold it to me and so did I.
 
rupedoggy

rupedoggy

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Yes, as pressure decreases the temperature a liquid becomes vapor decreases, or vice versa. Water will boil at room temperature if you pull enough of a vacuum.

Or, if your tank vent is not working correctly allowing air into the tank the tank willbe put under a vacuum and can boil at a very low temperature.
This is interesting. Just how much vacuum do you have to pull to boil water at room temperature?
 
Franny K

Franny K

xyz
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One day a few years ago I had a top handle chainsaw with the fuel toward the bar and the exhaust toward the rear do what is probably boil. I was cutting a perhaps foot diameter stump at ground level tapering deeper toward the center. After a while it did not want to go any more and I took the fuel cap off. It definably was making bubbles. As the bubbling settled down enough to see inside the fuel filter was the source of a whole lot of bubbles and the phenomenon kept going getting less for at least a minute. Only source of bubbles being the fuel filter. Perhaps the fuel filter was a catalyst of sorts. It was non ethanol 91 octane and amzoil pro saber if that matters.
 
Franny K

Franny K

xyz
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This is interesting. Just how much vacuum do you have to pull to boil water at room temperature?
You are basically asking what is the partial pressure of water in saturated air at room temperature. 68 degrees F is 20 degrees C
17.5 mm of hg 760 being atmospheric or
0.0231 atmospheres 1 being sea level
so getting close to a total vacuum like only 2.3% of the pressure before starting to pump out assuming sea level.

That is what I came up with

http://intro.chem.okstate.edu/1515SP01/Database/VPWater.html
https://en.wikipedia.org/wiki/Vapour_pressure_of_water
 
Huskybill

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I just purchased some self sticking heat shield for my dirtbike rear plastics were the heat of the muffler is. Or aluminum foil glued to the tank as a heat shield may fix it.
 
lone wolf

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Lots of drivers out there probably didn't know (or care) that gasoline is blended differently for summer or winter. Recently, though, that issue has been capturing headlines, thanks to a showdown in California, where Gov. Jerry Brown wants to allow the early use of the so-called winter-blend gas in a play to bring down spiking gas prices in the Golden State.

The price of gas is a confusing, convoluted issue. But before we get into that, what exactly is the difference between summer and winter gas, anyway? Basically, winter gas is cheaper but not as pure, and worse for the environment.

The nation has some 20 different blends of gasoline to meet overlapping state and federal guidelines. The reason for the different grades of gas comes down to trying to control VOCs (volatile organic compounds) that are more likely to evaporate the hotter it gets. More VOCs equal more smog, especially in summer, when the heat in the atmosphere increases the propensity for atmospheric ozone and adding in the VOCs increases the intensity of the smog.

The different grades of gas are measured on a system of RVP, or Reid Vapor Pressure, which is measured in pounds per square inch (PSI). The higher the RVP number of a particular gas blend, the easier it is to vaporize and the worse it is for the environment. All gasoline blends have to be below 14.7 PSI, which is normal average atmospheric pressure. Any number higher than that and gasoline would become a gas.

During the summer heat, the RVP of gas has to be especially low to keep it from boiling off. The EPA mandates an RVP maximum of anywhere between 9.0 PSI and 7.8 PSI for summer-grade fuel, depending on region (though you get a fudge factor of 1 psi for using gas blended with 10 percent ethanol). There are even lower RVP-rated fuels for cities like Houston, New York, and L.A. Different states and cities have their own rules based upon their seasonal temperatures—Washington state needs different summer gas than, say, Florida. That's why there are so many blends. To make it more complicated, the time for switching from summer- to winter-blend gasoline varies by state too.

Generally, the lower the RVP of a gas blend, the more it costs. For example, in winter you can blend butane, which is relatively plentiful and cheap, with gasoline. But butane, which has an RVP of 52 on its own, can't be used in summer, when it would immediately boil off as a gas. So "purer" summer gasoline is by default costlier. (And there are other factors at play too. More people travel in summer during peak driving season, for instance, putting more stress on demand.)

Back to California's woes: First, an August fire at a Chevron refinery diminished the ability of the oil industry to meet demand, driving up delivery times and transportation costs. That especially hurts in California, which has stricter standards than anywhere else in the nation as far as what blends it will sell, making the state especially vulnerable to supply issues.

So Brown's loosening of the rules on gas blends is an attempt to fight back against that vulnerability and bring prices back down. But there's no guarantee. Gasoline is a commodity, and yet the price-setting system has only a loose relationship to supply and demand. Rather than having an independent governing body oversee the supply side of the equation, suppliers voluntarily report on the supply of oil. And any time the numbers could be fudged for profit, we ought to raise our eyebrows.

 
catbuster

catbuster

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This is interesting. Just how much vacuum do you have to pull to boil water at room temperature?

Water’s vapor pressure at 73 F is 0.4080059 psi. Atmospheric pressure at sea level is 14.7 psi. You need to pull 14.3 psi, which if you put it as a percentage is ~97%. We would be dead & boiling before we saw water boil at room temperature.

Fuel (gasoline for all intents and purposes, there’s usually only 2-3% oil in mixed gas) has a much lower vapor pressure, which is why a blocked tank vent next to a hot saw leads to fuel boiling.
 
cus_deluxe

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Lots of drivers out there probably didn't know (or care) that gasoline is blended differently for summer or winter. Recently, though, that issue has been capturing headlines, thanks to a showdown in California, where Gov. Jerry Brown wants to allow the early use of the so-called winter-blend gas in a play to bring down spiking gas prices in the Golden State.

The price of gas is a confusing, convoluted issue. But before we get into that, what exactly is the difference between summer and winter gas, anyway? Basically, winter gas is cheaper but not as pure, and worse for the environment.

The nation has some 20 different blends of gasoline to meet overlapping state and federal guidelines. The reason for the different grades of gas comes down to trying to control VOCs (volatile organic compounds) that are more likely to evaporate the hotter it gets. More VOCs equal more smog, especially in summer, when the heat in the atmosphere increases the propensity for atmospheric ozone and adding in the VOCs increases the intensity of the smog.

The different grades of gas are measured on a system of RVP, or Reid Vapor Pressure, which is measured in pounds per square inch (PSI). The higher the RVP number of a particular gas blend, the easier it is to vaporize and the worse it is for the environment. All gasoline blends have to be below 14.7 PSI, which is normal average atmospheric pressure. Any number higher than that and gasoline would become a gas.

During the summer heat, the RVP of gas has to be especially low to keep it from boiling off. The EPA mandates an RVP maximum of anywhere between 9.0 PSI and 7.8 PSI for summer-grade fuel, depending on region (though you get a fudge factor of 1 psi for using gas blended with 10 percent ethanol). There are even lower RVP-rated fuels for cities like Houston, New York, and L.A. Different states and cities have their own rules based upon their seasonal temperatures—Washington state needs different summer gas than, say, Florida. That's why there are so many blends. To make it more complicated, the time for switching from summer- to winter-blend gasoline varies by state too.

Generally, the lower the RVP of a gas blend, the more it costs. For example, in winter you can blend butane, which is relatively plentiful and cheap, with gasoline. But butane, which has an RVP of 52 on its own, can't be used in summer, when it would immediately boil off as a gas. So "purer" summer gasoline is by default costlier. (And there are other factors at play too. More people travel in summer during peak driving season, for instance, putting more stress on demand.)

Back to California's woes: First, an August fire at a Chevron refinery diminished the ability of the oil industry to meet demand, driving up delivery times and transportation costs. That especially hurts in California, which has stricter standards than anywhere else in the nation as far as what blends it will sell, making the state especially vulnerable to supply issues.

So Brown's loosening of the rules on gas blends is an attempt to fight back against that vulnerability and bring prices back down. But there's no guarantee. Gasoline is a commodity, and yet the price-setting system has only a loose relationship to supply and demand. Rather than having an independent governing body oversee the supply side of the equation, suppliers voluntarily report on the supply of oil. And any time the numbers could be fudged for profit, we ought to raise our eyebrows.
One of the best posts ive read in a long while.
 
lone wolf

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One of the best posts ive read in a long while.
We had this happen one hot day last year we were right in between winter and spring and it was like 100 degrees out all the gas in the saws and stuff was boiling the pole pruner the the blower you frickin name it. When the climber opened the gas cap on the 200T and it blew up in his face he blamed me for f in up the saw and told me I was a crap mechanic! Well I told him a few things! I hate people that always blame others for everything! Just **** winter gas!
 
albert

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Thats when it happens. Warm/hot day late winter/spring while winter blend fuel is still being sold or in saws tank. It will happen in most saws old or new. Not just older models with the fuel tank being part of the metal crankcase. Had it happen on 372, 272, 70E, 5000+. Same day last year. The ms460 faired the best just took about 5 pulls to restart hot. Letting them idle a minute before shutting off and keeping them in the shade helps. If you have the time, pull the top cover off.
 
TheBrushSlasher

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If you have a plastic fuel storage container that isn't vented just it will give you a good idea of what your fuel is doing to your saws gas tank. If you have temperatures at 65 at 7 in the morning the container will be collapsed then as the temperature warms to around 90 the same container will be ballooned under pressure.You get a nice spray of fuel when filling a small tank if you don't vent the container before hand.

Your saws gas tank is going to get a little hotter and they DON'T vent as fuel expands only when fuel is cool and at a lower level to let air in because of emissions. After the saw has been ran a while then sat for 5 minutes or so you get a little heat soak and your fuel starts to expand more at temperature beyond the normal boiling point of gasoline because it's in a sealed tank.

Think of it like the cooling system on your car or truck, if you open the radiator cap when it's hot you get a geyser of hot coolant because that rapid release of pressure lowered the boiling and allows the liquid to expand rapidly until it equalizes. Winter and summer blend does this but winter blend will always do this when it's hot because of the lower vapor point.
 
2dogs

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Winter blend fuel is a problem. It will geyser much easier than summer blend. I teach saw use for the State parks and the Boy Scouts and both groups run saws near burn piles. The standard to fuel a saw is ten feet from the fire's edge but I advocate 20'. I also like a sawyer to run his saw until it is out of fuel, back away from the fire, then tilt the saw away while opening the fuel cap. Letting it sit cooling for at least 5 minutes is also a good idea as is putting a rag over the fuel cap when loosening it, but who carries a rag? It the sawyer is sprayed with fuel he can no longer work near the fire unless he at least changes his chaps.

The same general principles hold true for fuel cans. No Spill cans will turn into a sphere when they are left in the sun. The CARB metal self venting cans are the best but at almost $200 a piece only the gov't buys them. Try to keep fuel cans in the shade. Even Dolmars that are carried with the saw should be kept as cool as possible. MSR/Sigg bottles are pretty safe and will withstand very high pressure but only carry a quart at a time. I use MSRfuel bottles for my drip torch and my small saws (with canned fuel).
 
juanroberts

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From reading this thread, it seems causes (checks) include:

Lean jetting (make it richer)
Dull chain teeth (carry a file)
No lubrication (rev and check oil is flinging from bar tip unto a surface)
Winter gas (different boiling point)
Saw stalls heat the clutch

It seems a good idea on hot days is to keep the revs high so the clutch does not slip, the bar is getting more oil, and the air fan’s spin is kept high.

I noticed mine was boiling when I thought a bird was singing and when I stopped the motor it turned out the 338XPT was whistling like a tea kettle. Fortunately the gas cap has a rubber sleave/skirt that keeps the spray sideways. Mine bubbled for 20 minutes and when it finally subsided I could see the bubbles were coming from the gas line filter, so my guess is the actual boiling was taking place in or near the carburetor.
 

Nex

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Old thread - but in my limited experience the fuel boils in my Jonsered 450 (cast metal tank) all the time, while the Stihl 440 (plastic tank) never boils. And yes, I've run both saws with the same fuel, same weather on the same day (but not simultaneous due to a minor constraint with the number of limbs available to hold a running chainsaw)
 
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