Question: 5th Gen Fuel Consumption at Idle
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Ron4RNevada
New member
????
Sounds like you're trying to gestimate how long you can survive stuck on the highway in two feet of snow in Kentucky.
Sounds like you're trying to gestimate how long you can survive stuck on the highway in two feet of snow in Kentucky.
Engineer
New member
Hillbillies dont need fuel to survive
rocklighting
New member
I feel like this would be a.question we would normally be asking you...1/3 rule sounds close to my mpg math with the winter and my remote start.
1engineer
Moderator
1/3 seems to be what most manufactures are estimating. This may not be comparing apples to apples but Volkswagen has an integrated system into their vehicle that displays an estimated amount of fuel consumption based on electrical loads.
I don't always have the vehicle with me or extra time to test it out, but I'm wondering if it would be as simple as hooking up a fuel injection kit that runs to the fuel lines and is pressurized by shop air to the desired PSI with the vehicles fuel pump disconnected. We have one in the shop and it holds about 20oz of fluid, but we would have to determine the PSI that is running on our vehicles first to get a better test.
Just throwing out ideas in case anyone wants to test it out.
I don't always have the vehicle with me or extra time to test it out, but I'm wondering if it would be as simple as hooking up a fuel injection kit that runs to the fuel lines and is pressurized by shop air to the desired PSI with the vehicles fuel pump disconnected. We have one in the shop and it holds about 20oz of fluid, but we would have to determine the PSI that is running on our vehicles first to get a better test.
Just throwing out ideas in case anyone wants to test it out.
Ron4RNevada
New member
Well I don't have time today - But it would be interesting.
Should it be a hot start or cold start? I do know that my rig when leaving my house in the morning (at about 22F); resetting the econ gauge gets about 9mpg for the first four miles. Resetting it again after the four mile warm up it's getting about 19mpg. This is on a flat highway (with Toyo M/T tires) and driving a steady 60mph. 55 to 60 mph seems to be best in my truck.
If doing the "hot start" idle test I would drive four miles to the gas station; fill it up; start it and just let it sit idling for an hour. Then see how much fuel it would take to top it off again using the same pump hose. Some pump hoses shut off slightly earlier than some others.
Perhaps tomorrow morning - I'll take a good book along while I'm idling away an hour
Should it be a hot start or cold start? I do know that my rig when leaving my house in the morning (at about 22F); resetting the econ gauge gets about 9mpg for the first four miles. Resetting it again after the four mile warm up it's getting about 19mpg. This is on a flat highway (with Toyo M/T tires) and driving a steady 60mph. 55 to 60 mph seems to be best in my truck.
If doing the "hot start" idle test I would drive four miles to the gas station; fill it up; start it and just let it sit idling for an hour. Then see how much fuel it would take to top it off again using the same pump hose. Some pump hoses shut off slightly earlier than some others.
Perhaps tomorrow morning - I'll take a good book along while I'm idling away an hour
I had a 15 hour wait in Mexico once. I probably had about 12 hours of idle time and covered about 4 miles total. My rough calculations at the time were about 4-5 gallons burned. That's in the 1/3 gallon per hour range.
I wouldn't rely on that as a fact, but it's the longest idle time I've had.
I wouldn't rely on that as a fact, but it's the longest idle time I've had.
1engineer
Moderator
The only impact of a hot versus a cold start would be in the initial first start for around five minutes. The other 60 hours would be the same lol.
The reason for asking is just that: If you were camping, wrecked, blizzard, hurricane'd or other such disaster how long could your vehicle idle on a tank of gas?
Example:
We had a storm roll through here a few weeks ago and we (and about 5,000 others) were without power for almost three days in below freezing conditions. I have a generator of course and secondary heat sources but many people apparently don't think like I do and many resorted to their vehicles for heat and power, especially that first night.
Example:
Last year during a winter storm several thousand people got stranded on a section of local interstate for 12 hours.
That is my premise for the question. If my estimate of 1/3 GPH fuel burn is correct then you could go 60 hours continuously (with reserve) idling without refueling.
bimrunner
New member
I'm pretty sure that 1/3 is a good estimate to remain conservative. When I PMed you the other week I had been geeking out on the OBDII reader numbers. I am pretty sure I noticed my burn rate at idle when the engine was warm was right under 0.3 gal/hour. I didn't look at it extensively though. I believe I saw it changing by a few hundredths when the air would kick up a bit... its been getting spring-like here in CA...
KVA
Member
Great Quote! :bravo:
Before I bought myself a generator, I got through a few multi-day power outages by using a lead-acid battery -- 100Ah, I think -- to run my heating system (natural gas), the fridge, and the chargers for cell phones, and recharging it from the car's alternator when it got low.
Now I have a Honda 2K and it does make things a lot more convenient
jrandom
New member
marshal
New member
I can tell you that a large locomotive engine burns 5.5-6 gallons an hour idling.
Ron4RNevada
New member
Well if you're all satisfied with 1/3 gallon per hour I won't have to do anything.
LXRunner
New member
I'm going to elaborate on the calculations.
Let's assume a 4 Liter engine, idling at 700 rpm, and throttled to 25% of outside air pressure, which is what I have found typical in an idling engine.
The amount of fuel consumed depends on the amount of air consumed. The amount of air consumed is going to depend on:
Engine displacement (4L)
Engine speed (700 rpm, which is 350 cycles/min for a 4-stroke)
Volumetric efficiency - how efficiently the engine exchanges air
Manifold air pressure - how much is the engine being throttled?
For the sake of argument, let's assume the volumetric efficiency is 100%.
Let's also assume the engine is running at sea level on a standard 15C day, so the manifold air pressure is equivalent to the air density at sea level * 25% (because it's throttled to idle)
Air consumed will be:
displacement * cycles * volumetric efficiency * manifold air pressure
4L = 0.004 m^3
Air density is 1.225 kg/m^3 * 0.25
This gives us:
0.004 m^3 * 350/min * 100% * 1.225 kg/m^3 * 0.25
= 0.428 kg/min
Fuel used would be 1/14.7 , or 0.029 kg/min
Assume the density of gasoline is 719.7 kg/m^3.
that works out to 0.029*1000/719.7 = 0.04 L/min
0.04 L/min is 2.4 L/hr, or 0.64 gal/hr
If A/C, heater or anything else works, that will take more power from engine, increasing RPM, and per equation above eat more gas.
Let's assume a 4 Liter engine, idling at 700 rpm, and throttled to 25% of outside air pressure, which is what I have found typical in an idling engine.
The amount of fuel consumed depends on the amount of air consumed. The amount of air consumed is going to depend on:
Engine displacement (4L)
Engine speed (700 rpm, which is 350 cycles/min for a 4-stroke)
Volumetric efficiency - how efficiently the engine exchanges air
Manifold air pressure - how much is the engine being throttled?
For the sake of argument, let's assume the volumetric efficiency is 100%.
Let's also assume the engine is running at sea level on a standard 15C day, so the manifold air pressure is equivalent to the air density at sea level * 25% (because it's throttled to idle)
Air consumed will be:
displacement * cycles * volumetric efficiency * manifold air pressure
4L = 0.004 m^3
Air density is 1.225 kg/m^3 * 0.25
This gives us:
0.004 m^3 * 350/min * 100% * 1.225 kg/m^3 * 0.25
= 0.428 kg/min
Fuel used would be 1/14.7 , or 0.029 kg/min
Assume the density of gasoline is 719.7 kg/m^3.
that works out to 0.029*1000/719.7 = 0.04 L/min
0.04 L/min is 2.4 L/hr, or 0.64 gal/hr
If A/C, heater or anything else works, that will take more power from engine, increasing RPM, and per equation above eat more gas.
