We have quite a few threads here about how to get better MPG. With these trucks working like they do, especially the V10, and having to work our loads into cramped spaces, up eroded hills, down rough roads, etc, etc, I wonder how many folks take that into consideration. There are many gallons used where the truck is actually sitting still or just barely crawling.

For example if you're getting 14 MPG on the road, but idling for any length of time you're getting 0 MPG - that'll cut into your average pretty deep.

Just thought I'd throw that out there...just in case.

 

Very good point Big Orn. In Dec I did quite a bit of testing on some equipment we sell. I would set in the field and idle for qwhile then run for a while at 3-15 mph. Reapeat, repeat, repeat. Not suprisingly those tanks averaged 9.??. What bothers me is that I only in the 11s on much more consistant 70 mph trips with a little around town tossed in. Seems like there should be a bigger difference.

 

I tend to notice that prolonged idling will take a pretty significant hit in my fuel consumption. Prolonged idling and running the engine above 3000 RPMs seem to do that the most. Running it so it shifts at 2000-2500 seems to give me the best economy. If I had a manual, I would probably shift at 2000 RPMs around town, but this automatic is tuned more for towing and hauling heavy loads (which it's great for) which gives it slightly higher shift points than I want for around-town.

For me, the issue of idling is more one of engine longevity. My routine is to start the truck as soon as I get in it, and then let it idle while I'm getting the climate control set, putting myseat belt on, setting the radio, and plugging in the MP3 player. I don't shift out of park until all of this is done, or until all the lights on the dash go off, whichever comes first. This is to make sure all the fluids are flowing and, especially on cold days, to give the pistons and such a lower thermal gradient so as not to shock them.

When I come to a stop, I put the truck in park and usually let it idle for a few seconds while I take off my seat belt before shutting it off. This is more for cool-down time after running. This works well when I come home, since I'll stop at the top of the driveway to get my mail, so the truck has probably a minute of easy running before shutting it off.

When I went towing this past weekend, for gas stops (after running the engine pretty hard) I would let it idle for a few minutes. What I used there as my test was I would idle it until the exhaust stopped dinging from cooling, then I shut it off.

I'm used to aircraft engines more, which are significantly more sensitive to thermal shock. I'm sure I'm too nice to my V10, but at the very least what I do won't hurt it, and the minimal amount of idle time doesn't make a significant difference in fuel economy. It's when you leave the thing idling for long periods on end (think driving in stop-and-go traffic, or just leaving the engine running while you run inside to get something for a few minutes) that seem to have the bigger hit on MPG. Ultimately, gas is a lot cheaper than an engine rebuild.

 

Depending on your driving habits, there is.

For instance - for those that don't really work their trucks that much, their gains could be more than 5 MPG!!!!! But this can only work if you monitor your driving habits.

For others (those that tow most of the time) you are right, the difference wouldn't be that much, but still would improve significantly if they would just kill the engine now and then.

During my test, I realized that I idled the engine much more than I needed to, like wanting the AC to be at full blast and the cab cool after I finished loading my trailer and pulling and binding the load. Or, in the winter, idling for heat. I soon realized I could sacrifice a little creature comfort for better MPG.

So forth and so on...

 

Your points about idling for the AC and for the heat are correct - that's a great way to lose MPG. I'll agree it depends on use, but for my use I've found that the little extra idle time (that probably does nothing, but may extended engine life) seems to make a difference.

I'll only start the truck up in the morning on very cold mornings for some extra heat, but that's actually more to give the engine a little extra warm-up time. Big thermal shocks aren't good for anything, although whether or not this engine really cares is another matter.

Lubrication in the cold isn't a concern with these thin oils, really. When I was driving my old rusted '82 Jag as my only driver, starting it up in the winter with 20W-50 involved watching oil build up pressure for around 30 seconds, and hearing the valvetrain make noises until that heavy thick oil got up to all the passages. That couldn't have been good for the engine, and probably contributed to its dead rings (very low compression) and sloppy valvetrain by 170k when I took it off the road (it was perfect at 130k when I started driving it). Then again, my using the gas pedal as an on/off switch once the engine warmed up certainly didn't help, either.

 

Old habits die hard, huh?

I have a little sign in my office that reads:
If we always do what we've always done; then we'll always get what we've always got.

 

Well, I certainly drive the current Jag hard, but that's what I bought it for. I don't actually abuse the thing - shifts are always below redline, and I wait for the engine to warm up before I start beating on the thing. Interestingly, that engine doesn't like being driven easy. If I drive it easy for too long, when I stomp on it I will get a big cloud of smoke. This must make the Lexus or Infinity driver behind me (I usually make sure it's one of those) both scoff and cough.

The V10 I tend to drive pretty easy. Most of its use is semi-constant load at constant RPM with the cruise control set on the highway. I hardly ever stomp on it, and certainly not when it's cold. The engine seems to like this so far.

Around my office we say "The definition insanity is doing the same thing and expecting different results."

Being engineers doing experimental work, we are required to be insane and do the same thing over and over again to see if it will fail.

 

FWIW, my ScanGauge II shows that I use .75 gallons per hour (GPH) when idling.

 

That's really not as bad as I thought. I idle my truck every morning for 10 minutes. So by your calculations i only waste about a gallon per week. Sweet action!!!!