MPG at IDLE


#1

Do you know the MPG of a Ford F150 with a 6 cyl eng, when it is idling, after warm-up, driven about 10 miles?


#2

Let me re-phrase that, how much gas is it burning per minute or per hour?. the MPG is obviously ZERO.


#3

huh? MPG at idle is Zero, whether or not it is warmed up.

Unless you are coasting down a hill in idle — I’m assuming you are idling parked.


#4

fill up gas tank, idle for an hour, refill tank. See how many gal it took to refill.


#5

Let me ask the OP a question:
How many miles is the truck traveling while the engine is idling?

If, as I suspect, the answer to my question is “zero”, then the answer to your question is also ZERO.

Was this supposed to be a trick question, or perhaps did you mean to ask how many gallons it would use per hour? A more valid measure of gas consumption while idling would be to use time as a measurement tool since no “miles” are involved. Think about it.


#6

Guys, don’t be obtuse! The OP rephrased the question in the first comment: how many gallons per hour wil it burn?

Answer: Not many. Do as Bill suggested if you’re really curious.


#7

If I were working on the problem, I would use an ocilliscope to measure the pulse width of the injector ‘on’ time and do the math using the specified flow rate of that engines injector.

Let us know what solution you came up with.


#8

interesting. You would also need the idle rate, but the scope would give you that also.


#9

he rephrased it while I was composing my reply, and i didn’t see it till after mine was posted.


#10

I’ve heard for most engines it’s in the neighborhood of half a gallon per hour.


#11

If this is an OBD II vehicle, you might be able to get the injector rate from the PCM and a scanner.


#12

Yeah, I was interrupted while I was composing my reply, and after I posted it, I saw his clarification. Unfortunately, work sometimes interrupts more pleasant activities.


#13

Try minimizing your idling after you figure out your MPG on a tank of gas. Then figure the mileage again. You will find out how much you are saving by minimizing the idling. A 72 Buick Electra 225 with the 455 engine idled all night from 11 PM until 6 AM on about half a tank, (the front half of a tank). The other half of the tank was taken out by artillery. I know; you’re asking about the driver of the car. It was safely in the bag with the rest of the clubs.


#14

It depends on the size of the engine, the cam profile, and other things. Diesels idle more economically than gas engines as a rule because they aren’t wasting energy pumping air past a closed throttle. Toyota’s VVTi retards the intake valve timing at idle to lower intake manifold vacuum and with it pumping losses, or so I suspect. A Scan Guage II will plug into your OBD II and read out this info. The 1.5 liter Toyota Yaris engine uses .15 gph idling in neutral according to info I have gathered from Scan Guage II users.


#15

Maybe you can figure it THIS way . . . take your truck on a trip, get on the interstate and set the cruise control to 60 mph . . . then fill up and calculate MPG as nornmal (fillup before and after the test, divide the miles traveled by the gallons used). Let’s say your F150 will get 30 mpg highway . . . and the tach reads 2100 rpm during the time you are going 60 mph. You’re using 2 gallons per hour, 1 gallon per 1/2 hour, 1/2 a gallon in 15 minutes, 1/4 gallon in 7 minutes. If your warm-up RPM is 700 RPM, divide by 3. Approximate use in your warm-up is . . . however long your warm-up is . . . 7 minutes? Divided by 3? Not much at all. I know that this will be criticized as unscientific and almost retard math . . but it is approximate . . . certainly a lot less than you might think you use during warm-up. I know that warm-up is higher RPM, richer mixture and so forth . . . but certainly not a lot of gas use while idling, after warm-up and after being driven 10 miles as the OP said. Less than a pint? Whew! I have a headache now. Rocketman


#16

Getting a gas fill up while traveling at 60 mph is a good trick!
(sorry, couldn’t resist)


#17

C’mon Bill . . . :0) Rocketman