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Finding: BUSTED
Explanation: If you drive a pickup, common sense might lead you to think that opening the tailgate on the road is the more fuel efficient way to go. In fact, the idea that tailgates block airflow and increase drag became widely circulated, and some truck owners intentionally drive with the tailgates down to ease up on gas consumption.
But when MythBusters Jamie Hyneman and Adam Savage drove identical trucks under the same conditions across the desert — one with the tailgate up and the other with it down — Jamie's tailgate-closed pickup outlasted Adam's by more than 30 miles (48 kilometers).
Closing the tailgate actually improves fuel efficiency because it creates a type of airflow called a separated bubble within the bed of the truck. As wind rushes over the moving truck, that bubble of slow-moving air deflects it over the raised tailgate. By guiding surrounding air over and across the bed of the truck, that vortex effect prevents added drag.
However, driving with the tailgate open eliminates the bubble effect, pulling the air toward the truck bed and creating more drag rather than deflecting the wind. Some gas-conscious pickup drivers still swear by leaving their tailgates open, but science sides with leaving it up.
It is more fuel efficient to drive your pick-up truck with its tailgate down, rather than up.
BUSTED
Driving with the tailgate down actually increased drag on the pick-up and caused it to consume fuel faster than the identical truck driven with the tailgate up. It was later revealed that the closed tailgate creates a locked vortex flow that created a smoother flow of air over the truck. With the tailgate down the trapped vortex was dissipated and the drag increased.
(This myth was revisited in episode 64 and re-busted. However, it was found that mesh tailgates are the most efficient configuration.)
Looks like their notes state the mesh is 5% better, so lets say a $31.59 mesh tailgate (Bully Tail Gate Net from Real truck.com, free shipping) 9% sales tax, $34.44 all-together.
Tailgate up: 1,136 miles (round trip) from Sheffield AL to Skeeatuuk OK, we will say 19mpg, so 59.79 gallons of gas @ $2.34 a gallon (Don't get gas in OK, it was the highest), $139.90 with your tailgate up.
Mesh tailgate: $34.44, 5% more efficient @ 19.95mpg, 1136 total miles, 56.94 gallons, or $133.24.
Looks like the mesh tailgate will have paid for itself after 5,860 miles!
There's a man that knows how to use a spreadsheet. A man after my own heart.
So, with that 5% and expecting maybe another 5% from the chin spoiler, plus a little more from 1 or 2 degrees of initial timing and a touch from synthetic rear axle lube, and a bit more from the mirrors, maybe a true increase of 5%?
Seriously though, David, you got 21.81 MPG going home from the GTG last year. Adding 5% more to that would make it 22.90 MPG. So, can we shoot for an even 23.00 average on the way home this time?
I think your idea of smaller mirrors is a good one. And I'll check out the later chin spoiler as a good friend has a '93 with one and I can measure it to compare to Rusty's bumper. Or, perhaps take it off his and see if it'll fit Rusty. (He will be happy to let me look it over as he brought his truck over yesterday due to a huge oil leak that has kept it off the road for at least 6 months. In fact, it was sooooo bad that we tied an old piece of carpet under it before he got to my driveway or it would have left a black stream. He said it was the pan gasket, but on the lift I pointed out that it was from the oil pressure sensor. A trip to O'Reilly's and an expenditure of $10.86 had him back on the road and grinning ear to ear!)
Does 23 MPG sound good enough, or should we shoot for 24?
What about deleting the p/s door mirror all together? Pretty sure you would only need a d/s door mirror and rear view mirror in the states you are traveling in.
What about deleting the p/s door mirror all together? Pretty sure you would only need a d/s door mirror and rear view mirror in the states you are traveling in.
Thanks. And actually, the P/S swing-away mirror could just be folded in toward the door.
I once had a Geo Metro Xfi, which was the high-mileage champ of that time era. There were several modifications to the regular Metro in the making of the Xfi and one was that the passenger door mirror was deleted. Every little bit helps!
My buddy brought his '93 over yesterday and we examined the chin spoiler on it closely. The bottom line is that I do not think it would be easy to adapt that chin spoiler to work on our bumpers. Nor to adapt that bumper and spoiler to our trucks.
Having said that, here are some measurements, observations, and pics that back up that position. However, someone more ingenious than I might see something I missed.
First, here are a couple of pics of the spoiler on the truck from the outside:
Next, the later bumper's bottom edge is turned straight up for a distance of about 1", and that's used to rivet/bolt the spoiler to the bumper, as shown in the next two pics. My first thought was that we could make a piece out of angle to bolt to the bottom of our bumper and the spoiler would bolt to that. But, if you look at ours the bottom actually angles down, so the spoiler would bolt on at an angle and the outside ends wouldn't touch the bumper.
And, there are several other differences that suggest it wouldn't be a good fit:
Flat on front: Our bumpers measure ~50" between the points where they bend back slightly. But the later bumpers are rounded rather than flat between those two points, and they are only 43" apart.
Sides: Our bumpers have an angled part on each side that is about 12 1/2" long, while the later bumpers have sides which are 14 1/2" long.
Ears: And our bumpers have 2 1/2" segments on each side that go straight back. However, the later bumpers have ears that are 5 1/2" long.
And, while the spoiler is somewhat flexible, I'm afraid those differences would make it difficult to adapt to our bumpers. So, we ought to look for a different spoiler - something that is about the size of the later ones, which are 4" tall. But, if someone can think of another way......
Comparing mpg of same time frame before and since 9/13/14 OK GTG.
As I was updating my gas mileage records in the permanent file [as opposed to temporary storage in my wallet ], I started thinking about the upcoming OK GTG [10/3/15]. The last meeting was where initial timing adjustments [18 down to 14 BTDC] were made as well as adjustments to the distributor vacuum canister, following that. I decided to check my average gas mileage since the OK GTG and compare it to the same time frame from 1 year prior.
As I compared the two periods of time, I deleted any tank which had been used while driving on highways. The reasoning behind this is that the year prior, the truck was driven very little other than the normal route to and from work plus weekend duties. The period including the OK GTG reflected 1100+ miles of mostly highway driving, which would skew the results.
The last OK GTG was held on 9/13/14.
Gas mileage average for the period of 9/23/14 - 8/19/15 [most recent fill-up] = 18.94 mpg.
Gas mileage average for the period of 9/26/13 - 8/21/14 = 16.65 mpg.
As I went back through the records to refresh my memory, most likely the main contributor to the gas mileage increase was when it was discovered that the two electrical leads from the DS2 distributor to the MSD box were reversed, which had electronically advanced the timing to such a degree that the vacuum advance could not be used. The truck was being driven with the vacuum line to the canister being plugged [no vacuum advance]. Once the wires were corrected, the vacuum advance could be used. This was done prior to the OK GTG, but the overall timing was enhanced by the collective team in OK [Thanks, guys!].
Soon, another OK GTG will take place and at that time, the transmission and differential gear lube will be changed to synthetic. I am in hopes that this will narrow the gap in gas mileage when comparing summer to winter driving. The normal [for my truck] variance is 1 1/2 to 2 mpg less in winter. Of course, some of this is inherent with winter blend fuel, but some may be due to thickened viscosity of the standard "dino" based lube.
08-19-2015, 11:29 AM
], I started thinking about the upcoming OK GTG [10/3/15]. The last meeting was where initial timing adjustments [18 down to 14 BTDC] were made as well as adjustments to the distributor vacuum canister, following that. I decided to check my average gas mileage since the OK GTG and compare it to the same time frame from 1 year prior.