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Minneapolis Moline Tractors Discussion Forum
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Frost on the Manifold

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JKC

02-15-2004 07:40:23




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I have two tractors that develope a thick layer of frost on the intake manifold above the carberator after the tractor warms up. What causes this? I know that it is not suppose to be that way. Any help would be much appreciated.

Thanks very much.




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RUSS

02-17-2004 03:57:41




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
FROSTY ; AS YOU NOW KNOW FROM ALL THESE STRINGS THAT MANIFOLD CONDENSATION OR FROST IS NORMAL DEPENDING ON CONDITIONS. THE DETAILS CAN BE FOUND IN PHYSICS AND/OR THERMODYNAMIC TEXTS.
LOOK FOR A FORMULA GIVEN AS (PV = nRT) GIVEN IN ONE OF THE PHYSICS/THERMO CHAPTERS.
NOT TO WORRY IT IS NORMAL HERE ON EARTH AND WOULD INDEED BE ABNORMAL ON OUR MOON AND ALSO
ON MARS DUE TO THE ABSENCE OF OUR EARTH ATMOSPHERE. JUST AS WELL BOTH OF THOSE SURFACES ARE REAL ROCKY AND TOO FAR AWAY FROM THE CONSUMER MARKET.

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Steve

02-16-2004 14:24:44




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
The other part of this equation is the gasoline itself. Each liguid as it evaporates absorbs a certain amount of heat (latent heat of vaporization). As the fuel is added as a liquid, all be it in a small stream, it vaporizes and absorbs heat in the process. Thus the lower temperature after the carb. The temperature produced can be predicted knowing pressures and characteristics of the fluid being evaporated.

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Randy

02-16-2004 07:52:57




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
You could cure it by installing a heat duct to bring hot air from around the exhaust manifold to the air filter inlet and on to the carb.



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dlp

02-15-2004 18:54:00




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
Here's my 2 cents worth. I agree that this a common occurrence, this happens with aircraft & is why they have carb heaters. When the air goes through the venturi it speeds up & I guess the temp drops also. The humidity of the ambient air outside condensates on the manifold, how much depends on the humidity level & temp of air going through the carb. The way I understand it, it will actually try to ice up internally, but warms up as it hits the area where the intake/exhaust joins & causes the gas/air mixture to expand & vaporize again. A pilot once told me that icing can happen up towards 60df if the conditions are right. If I am wrong on any of this please correct me!

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JKC

02-15-2004 17:38:52




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
Sorry, I should have said..... both tractors are gas fuel.....My MM ZAU does it in both summer and winter, and my Jetstar 3 Super has just started doing it while I was moving snow. Thanks for the input guys.



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Roger

02-15-2004 17:28:07




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
My Case 930 gasoline does it too, dont worry about it, it stays frosty the whole time I'm blowing snow. I don't know if my 930 propane will do it or not, I don't use it in the winter. I haven't noticed any frost on the 830 propane though



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Bob K - explanation

02-16-2004 09:55:40




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 Re: Re: Frost on the Manifold in reply to Roger, 02-15-2004 17:28:07  
Propane tractors have a regulator that drops the high pressure in the tank to a low pressure for carburetion. The regulator has warm coolant from the radiator flowing through it (once the tractor warms up) to keep the reduced-pressure fuel from being so cold when it goes from high to low pressure. My theory on why a properly set-up LP tractor doesn't frost up like a gasser is the fact that the LP is already vaporized before it hits the carb so there's less temp drop in the intake manifold. Converting gasoline from a liquid in the carb to a vapor in the manifold/intake tube absorbs a lot of heat. As others have said, outside temp and humidity are big factors on determining the amount of condensation/icing on the manifolds and intake tubes. As long as the tractor runs okay, it should not be a concern.

As mentioned elsewhere in this thread, airplane carbs use heat from the muffler to keep their venturis from icing up. Lives have been lost due to this phenomenon.

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Kelvin

02-15-2004 13:37:25




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 Re: Frost on the Manifold in reply to JKC, 02-15-2004 07:40:23  
Are your tractors on gasoline or LP? I'm aware you can have problems with lp manifolds on gasoline tractors.



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Joe Leising

02-15-2004 16:24:32




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 Re: Re: Frost on the Manifold in reply to Kelvin, 02-15-2004 13:37:25  
I am gonna try to remeber my physics a little here. I do not think it is necessarily a bad thing that this happens. My guess is that the expansion of the air after leaving the venturi of the carb is causing a cooling effect. This causes the frost to form. This is similar the the frosting that occurs on an LP tank when the LP is pulled out fast enough. The compressed stuff is allowed to expand. This expansion causes a cooling effect.

Just a guess

Joe

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