Evaporative Fuel Loss On A Hot Day

CGID · Apr 5, 2018

I have a '48 Farmall Super A. While stored indoors, during any season, the gasoline fumes that leaked past its original gas cap seemed strong enough to create a near explosive atmosphere inside the shed. For any tractor with that type of gas cap: While using the tractor on a blazing hot day, did the fuel that evaporated out of the gas tank figure into the machines stated fuel consumption rating? And, I have replaced the old style cap with new.

Indiana Ken · Apr 5, 2018

That would depend on how the test was conducted. If the fuel tank or container was weighed before and after the test, then yes fuel loss to evaporation would be counted as fuel consumed even though it was not burned in the engine. In the case of my dyno, it uses a separate fuel flow meter that measures fuel going to the engine. Fuel lost to evaporation is not measured by this instrument and therefore not included in the fuel consumption calculation.

Eldon (WA) · Apr 5, 2018

I always had more gas evaporate overnight in my tractors

CGID · Apr 5, 2018

Exactly! Mine sits most of the time now. I never kept a lot of gas in the tank, but before I changed the gas cap, it would go dry between uses. Outside, on a hot day, the gas evaporating past the cap must have competed with the gas going through the carb.

Roger in Iowa · Apr 6, 2018

If you can smell it, you better be looking for a leak and not evaporative fumes... I have 7+ in the shed and don't smell any fumes, summer or winter.

Blackhole49 · Apr 6, 2018

I have an A, along with 7 others, the only time I sell gas in the shed is when something is leaking (usually when I forgot to shut the gas off at the sediment bowl).

CGID · Apr 6, 2018

The fuel system is tight. If you can find an old-style gas cap to fit one of your machines, put it on and see what happens. The shed the tractor is in is weather tight and does not provide much if any ventilation. With the old style gas cap, the fumes in the shed would become overwhelming. The new gas cap eliminated the problem.

CGID · Apr 6, 2018

That's a beautiful A! As for gas fumes, how weather tight is your shed?

centash · Apr 6, 2018

I agree with Roger. With a proper gas tank cap and no leaks, there should never be any scent of gas in your shed.
Ben

Blackhole49 · Apr 6, 2018

Tight enough that you smell gas every time just a little bit leaks on the cement. Also, the tractor sits for 8 months with no drop in the tank.

MarkB_MI · Apr 6, 2018

My guess is fuel consumption on most early tractor tests was measured by filling the tank before and after each run. So evaporative losses would have been included. And I think later tests might have used some sort of fuel flow totalizer to measure actual engine fuel consumption, ignoring evaporation.

Regardless, the loss to evaporation shouldn't be that significant. Suppose a tractor under full load was burning 5 gallons per hour, plus losing a pint (.125 gallons) to evaporation. Evaporative losses would have accounted for less than 3 percent of total consumption, probably within the measurement margin of error.

JMOR · Apr 6, 2018

I have been using a 560 gallon outdoor overhead gas tank for decades & if evaporation were a problem, I would know by now.

CGID · Apr 6, 2018

Thanks for all the replies. I knew the original owner and his son. Neither were surprised by the fumes in my shed as they had problems being around the tractor while it was in their barn. I guess this tractor had a gas cap with a bad seal from day one.

Evaporative Fuel Loss On A Hot Day

CGID

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Indiana Ken

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Eldon (WA)

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CGID

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Roger in Iowa

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Blackhole49

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CGID

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CGID

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centash

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Blackhole49

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MarkB_MI

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JMOR

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CGID

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