7.3L Fuel Consumption at Idle

TJ Carr

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Was stuck on the interstate for almost 3.5 hours the other day due to a semi crash & fire that totally blocked the road

Anybody know how much fuel the 7.3L uses when idling & just running the lights, heater/radio in park?
 
I couldn't find anything specific to the Ford 7.3L, but there are a couple of gov't papers out there over the years that list medium-duty gas trucks at around 0.85 gal/hr while idling. Probably a decent guestimate.
 
I find this post as I noticed that my 7.3 went from 14.2 MPG from a couple hundred miles. Today I lost it run idling for about an hour and found it dropped drastically to 12.8.... Something is not right here. Low idling RPMs, no hills, no stop and go.... What gives, how in the hell does idling cause this poor milage? I know the calculator is off and my real world according to Fuelly is 12.7 overall.
 
I find this post as I noticed that my 7.3 went from 14.2 MPG from a couple hundred miles. Today I lost it run idling for about an hour and found it dropped drastically to 12.8.... Something is not right here. Low idling RPMs, no hills, no stop and go.... What gives, how in the hell does idling cause this poor milage? I know the calculator is off and my real world according to Fuelly is 12.7 overall.
It’s Miles Per Gallon. Your idling but not going anywhere, which in turn will lower your MPG.
 
Yep, I’ve noticed mpg drops like a rock when idling.
 
Its a huge displacement gas engine with no cylinder deactivation or auto start/stop (which is a good thing for longevity), so its not gonna be efficient idling at all, maybe the worst of any light duty vehicle. I dont think you will ever see another motor like this manufactured, I think its great if you like to keep trucks forever, but with fuel so expensive it does put a damper on it...
 
Was stuck on the interstate for almost 3.5 hours the other day due to a semi crash & fire that totally blocked the road

Anybody know how much fuel the 7.3L uses when idling & just running the lights, heater/radio in park?
I can’t help but laugh at the part about running the lights, heater and radio part. I can’t imagine that that has any affect on fuel consumption, unlike running the AC compressor
 
I can’t help but laugh at the part about running the lights, heater and radio part. I can’t imagine that that has any affect on fuel consumption, unlike running the AC compressor

Just think how a electrical vehicle would do lol
 
Have not seen TJ Carr in a few months hope he is ok!!!!:)
 
My mother in law once told me that my truck was so bad on fuel because of my heated steering wheel. Haha.
 
Have not seen TJ Carr in a few months hope he is ok!!!!:)
Yeah you’re right he hasn’t been around in a while, couldn’t remember if it was him or you but a while back we were talkin about knives and such I ended up buying a bark river gunny cpm3v that either you or him recommended
 
Plugged in my OBD MX+ and took a few screenshots to capture the fuel flow. Both are idle, park, ~86F

With A/C:

Screenshot_20220625-182954.png


A/C off:

Screenshot_20220625-183022.png


I tried to capture the median value both times. If you calculate air/fuel they are both right around 14:1 which I would expect at relatively no load at idle. Not sure where the 7.3 is at for idle stability but most like to be a bit rich so the idle speed doesn't have to be increased... Maybe I'll plug the scan tool in next time I am out driving and capture the values in gear/stopped at a light, etc.
 
wow too cool! thanks modman!
 
Your thirsty 7.3 will literally drink itself to death at idle for anything longer than a stoplight. You should probably get some spare fuel tanks and a AAA card if you have to idle a bunch in traffic.

I've also heard the idle-thirst of the 7.3 will 'suck' so hard that it will distort/implode the structure of the fuel tank.
 
Your thirsty 7.3 will literally drink itself to death at idle for anything longer than a stoplight. You should probably get some spare fuel tanks and a AAA card if you have to idle a bunch in traffic.

I've also heard the idle-thirst of the 7.3 will 'suck' so hard that it will distort/implode the structure of the fuel tank.
That's why I buy her so much to drink! 😂
 
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