Hypermilers thread

[460/5]

Originally Posted by David85 Got back from another trip loaded this way for both directions: Unfortunately, I think I overfilled the tanks slightly when I got back. The fuel gauge pegged 1/4 past the "F" mark and It doesn't usually do that. This represents quite a dilema on how to get accurate MPG results because the factory fuel gauge can be so inaccurate. How can I be sure that the tank is filled to the same level each time. My best guess is that I reached 20 MPG. I'm thinking of adding a marker in the filler flute of the tank that I can see when I fuel up to verify that there is same amount of fuel in the tank each time I pull out of the cardlock. For the next trip, I think I will just run on the single tank for both directions to eliminate one of the two possible sources of error. The larger the fillup, the more accurate the result will likely be. New tires are also on the way and should be on by the time I'm ready for the next trip. Right now, all of my tires are out of ballance and at least two of them are out of round ok. idk if this was said or not, because im too impatient to read the whole thread. run one tank dry, fill it with an exact amount, and run it dry again. then you will have your fuel mileage to a tee. i do this all the time on my 460. honestly dont know if its kosher to do that to a diesel, but its and idea.

[Chevy 6.2D]

The power is OK, but nothing out of this world. My 0-60 is 15-16 seconds shifting at around 3400. I haven't checked that since I fixed all my air leaks- that could've cut a lil.

The oil pressure is fairly low, or the gage isn't reading right (it sits halfway between red line and the "n", about 1/8 to 1/4" into the while line)
Truck has 204K, and some blow-by, but it's not too bad. The IP and injectors have less than 20K on them (PO is a honest guy, I believe him)

[David85]

460/5

I have run out of fuel a couple times on the highway and while its not the end of the world, its not really good for the fuel injection system either (fuel provides lube). I prefer to simply average tanks instead, although your idea would be one way to eliminate fuel up error for a one time test senario. However, I haven't been seeing much in the way of errors from the fillup pump.

Chevy 6.2D

1988 doesn't have a real oil pressure gauge. Instead it simply has an on/off pressure switch that turns on at the 7 psi mark. Your low oil readings are probably due to a weak connection at the sensor. You can change the sensor and mod the cluster to read dynamically like trucks older than 1987, but most just go with an aftermarket gauge instead.

Power seems to be on par for a non turbo diesel. Economy is lower than what it could be though. Without knowing more its hard to speculate on what could be wrong. Timing is the only thing I can think of.

[Dave Sponaugle]

With the way the tanks are in these trucks, the only real way to figure fuel mileage is averaging several tanks.

The slightest difference in how the truck is sitting can cause the front tank to take a lot more or less fuel since it is so long.

Rear tank is not as bad, but front end up or down hill does make a difference.

When I fuel, I use the same pump, drive in the same way every time and fill the spouts completly full.

The MPG changes every time.

[David85]

Front and rear tanks seem to be pretty consistent for me. Station lot is completely level so thats not an issue either. I've been running the same route, fuel fillup pump, and conditions for the last 3 years now. Lately I know how much fuel I burned before I put the nozzle in the filler flute. I got pretty good with my F150's fuel up numbers too back when I was still driving it. Some gas station attendants were surprised but I don't see what the big deal is in when you stay with one vehicle for so long.

MPGs do vary, but I found that has more to do with traffic, my driving style and weather conditions than the shutoff of the pump. Cool damp (but not raining) days like that last one consistently give me 20 MPG, while rainy days consistently keep me below 18 MPG. Rain and wind cap me at 16 if I insist on holding the speed limit.

I had railings in the bed on the way home so the tailgate was down and some parts were hanging out the back by a few feet. Doesn't sound like much but it adds up. Thats why I wasn't able to quite hit 20 this time. If I limited myself to 70 top speed I probably could have made it. The one time I hit 22.5 MPG in this thread was with a "load" so small that I had the gate up for both ways and box was practically empty. That almost never happens.

The results are accurate enough for me to consistently average better MPGs heading north than south no matter what tank is used in either direction. Reason being the prevailing winds near the highway route.

Using larger fillups also helps reduce errors. Filling up with 3 gallons won't be as accurate as 15. Thats another reason I stopped switching tanks at the halfway point. I'm only interested in the average, not how a slight tailwind can skew the results. Now that I know the reason behind the north/south direction discrepancy, there is no point measuring it everytime.

Wonder what a bumper to bumper bellypan would do for a truck like this, but I don't have time to build something like that. Maybe some day.

[Chevy 6.2D]

That's what I thought, I have a mech OP gage lying in the garage somewhere, have to find the line for it or get a new one.

My MPG could be somewhat due to the front brakes dragging. I hope to get those fixed in a few weeks.

I need to get my hard cold starts figured out. I either need batts, and alterntor, or both.
While the glows are on the volts are down in the red, after it is running, the volts stay around 10 for a while. When the glows cycle (engine running) the gage barely goes up when they turn off. I have seen other trucks where the gage quickly jumps up.

After glows are off it takes a few minutes but the volts eventually come up to 13 or so. I'm thinking replace the alt first. A 90 AMP lifetime warranty is $90 from o'reillys