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Heat soak

NPKenny

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The 562 and 550xo v1 discussion made me want to further my understanding of heat soak.

It’s approaching summer in the desert. I’m native to AZ and the summer means lots of daylight, so I still work outside like normal, maybe even more.

The other day I needed to remove a few trees and my recently rebuilt, and dead reliable 272xp began to get weak and would die off throttle. Switched to my recently built 288xp because I might as well. Exact same symptoms. I started with a 200t and it was really off from normal, but wasn’t dying. No amount of carb adjustment was working on any of the saws

Fuel was fresh non-ethanol with Amsoil Sabre 40:1.

Does this sound like heat soak? It was easily 105*F while cutting? What temperature equals heat soak conditions?

Are there better suited saws for the heat?
 

ayoungtexan

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Definitely heat soak and vapor lock. I was bucking some oak in the middle of summer with my grandfathers 046, it had severe vapor lock after sitting in the sun for 5 minutes. ‘Bout threw my whole arm out trying to restart it.
 

NPKenny

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105? Damn. If I were you I’d be waking up earlier and doing my cutting in the early morning hours when it’s cooler out.

It doesn’t exactly work that way here. We take advantage of any cool time as well, but it can be triple digits at midnight and 6am. Work usually still goes on.

I do a lot of farm work and water well work. I took a remote thermometer out on a well site to record operator exposure while the pump rig was over the well. It was over 140* at the operator station and 130* plus on the ground. It burns your feet more than anything. It’s not always AC and it not always on sale. We get pretty used to working in the heat.

The point of the question is more along the lines of am I losing my mind or is heat soak a real thing?
 

ayoungtexan

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It doesn’t exactly work that way here. We take advantage of any cool time as well, but it can be triple digits at midnight and 6am. Work usually still goes on.

I do a lot of farm work and water well work. I took a remote thermometer out on a well site to record operator exposure while the pump rig was over the well. It was over 140* at the operator station and 130* plus on the ground. It burns your feet more than anything. It’s not always AC and it not always on sale. We get pretty used to working in the heat.

The point of the question is more along the lines of am I losing my mind or is heat soak a real thing?
Heat soak is for sure a real and problematic thing in saws and other OPE. It’s so bad in my Stihl KM91 and BR450, that fuel sprays out of the tank when refueling. The gas also appears to be boiling in some cases
 

Terry Syd

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You may be able to decrease the heat soak if a saw has an 'Air Injection' system. The Air Injection system takes fresh air off the flywheel that could be circulating around the cylinder fins.

I had modded a 450 Husky to where I thought it was going to seize. The piston was touching the cylinder all the way up to the crown and the plug was white. The more I modded it, the more air it consumed and the less air available to cool the engine. It was not only making more heat as I modded it, I was also loosing air across the fins.

I blocked off the air injection system with some silicon sealer and put a couple of holes in the back of the saw to draw fresh air into the air box. The temps dropped right down, the plug was now a nice chocolate brown and the piston was running cooler. Surprisingly, the filter stayed cleaner as it wasn't sucking sawdust off the bar through the front of the recoil cover.

EDIT: A two-stroke can loose up to 20% of its power through heat soak. A flash reading on a dyno can show a heap more power than a long pull on the dyno.
 

Willard

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My 8 year old tree service 562XP has been a reliable saw over the years.
But even after a muffler mod years ago to help relieve engine heat for the AutoTune, it still needed to be hot started on fast idle.

Well a couple of weeks ago I modified the top cover by adding a heat vent like what's on the new 562XP, except I made the hole twice as big and removed the cover's bottom lip right below the vent.
Result...no more fast idle for the last 2 weeks . Totally different saw Should have done this years ago.

So my plan is for cold weather winter cutting I'll have a spare non vent cover.
20200603_212116.jpg
 

Al Smith

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An example .A few years ago myself at over 60 years old with a helper at the time bucked over 6 cords of ash in 96 degrees weather I alternated between a Mac 700 and and a modified Stihl o38 mag .On a gas up the Mac would be over heated ,the Stihl never failed to start .I ran at my own pace ,drank gallons of ice water and never peed a drop.My helper ran like a house afire .He vapor locked not me .Poor guy was tuckered out and 16 years younger than myself .I sat on my patio and drank beer while he exclaimed to my wife in the air conditioning "I can't believe that old man man out worked me ".She replied he's been at a day or two more than you.--A man's got to know his limitations they say .-----It's all in the design of the saw .Some cool good some do not .
 

Al Smith

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Here's another example also years ago .PM 610 McCulloch ran fine started fine except after several hard runs .It took me a while to figure it .Horizontal cylinder the chips clogged up the air flow on the bottom side .After a period of time this heat build up caused the electronic ignition coil to fail . By just periodically removing the covers and giving it a good blow out the problem went away .
 

rogue60

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I have all kinds of problems in summer here using pump gas even none ethanol fuel in saw's. All pump gas is rubbish here now days it's usable in winter and cooler days but peak summer temps is unusable if you actually want to get something done and not mess with saw's not re starting running rough stalling off idle..
Anyways Avgas solved all my problems running a saw or even a 2T mower on very hot days.
Avgas doesn't throw the towel in if it's a little warm out just like pump gas used to be good fuel but that's just a distant memory now days..
I to used to blame all my ope equipment for all these heat issues lol
 
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av8or3

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I have all kinds of problems in summer here using pump gas even none ethanol fuel in saw's. All pump gas is rubbish here now days it's usable in winter and cooler days but peak summer temps is unusable if you actually want to get something done and not mess with saw's not re starting running rough stalling off idle..
Anyways Avgas solved all my problems running a saw or even a 2T mower on very hot days.
Avgas doesn't throw the towel in if it's a little warm out just like pump gas used to be good fuel but that's just a distant memory now days..
I to used to blame all my ope equipment for all these heat issues lol
Avgas is blended with a much higher “vapor pressure” than automotive fuels because it’s used at altitudes where there is less atmospheric pressure to keep it in liquid form. Vapor lock (some call it heat soak) occurs when the fuel is heated and atmospheric pressure can no longer prevent vapor bubbles from forming in the fuel lines and passageways inside of carburetors. While I don’t condone Avgas use in power equipment I can see where using it in this case would absolutely solve this problem. It has nothing to do with octane, it’s all about vapor pressure. I will say that Avgas is loaded with lead (tetraethyl lead) and is harmful if breathing the exhaust and the lead will eventually lead to problems with the equipment it’s being used in. But it will indeed cure vapor lock.
 

Terry Syd

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Rogue, what octane of Avgas do you run?

I used to run 100-130 Avgas in my desert racer, great fuel, but a bit overkill for a saw.
 

av8or3

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Different octanes in Avgas are identifiable by the color of the fuel. 130 is Purple, 100 is Green and 100 LL (low lead) is Blue. For your information, 100LL has 7 times the amount of lead in it as leaded premium car gas had in it back in the day.
 

Terry Syd

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130 is Purple,

Back when I was in the Army and flying OH-13s (1967) with a heap of instrument accessories for 'instrument flight school' the turbo assist was 30 psi of boost for 30 seconds on a hooded take-off.

The fuel was PURPLE, it was 115-145 octane (lean to rich mixture). I've never seen that fuel again. I doubt my race bike would have needed that octane, but then in a pinch it might have been nice to have during the summer running up a hot sand wash.
 
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