Slow Down and Save...Gasoline

Hello. Most advances in science come when a person for one reason or another is forced to change fields.

I am from Mauritania and also now'm speaking English, give true I wrote the following sentence: "Everything you need to know about getting pregnant, conception, infertility, charting."

Best regards ;-), Dallas.

Dallas of KS 12:37AM February 23, 2009

I know from experience that diesel engines use considerably less fuel at lower speeds due to their high torque at low rpm and drastic loss of torque as rpm is increased. My analogy has always been comparing the long piston stroke to riding a bike in low gear.... you pedal very fast but aren't really getting the work done. Howbeit, I'd appreciate it if someone could expound on that thought.

I've analyzed fuel mileage in my 2001 FORD 7.3 PowerStroke Diesel truck to extreme lengths. I found that the digital readout for current MPG was extremely accurate at all speeds as I compared it with fill up tests on trips of at least 350 miles at various speeds. At 70 mph without using cruise control (cruise causes the accelerator to fluctuate, thus causing lower MPG) this 7800 lb. vehicle gets 19 MPG, at 60 it gets 22 and at 55 I can get 25 MPG. On level ground the best reading was 28 MPG at 43. This was the slowest I could test due to it coming out of O.D. at 42. The digital readout has taught me two important things: Driving slower with the vehicle gives incredible increases in MPG. Secondly, I found that the best MPG was attained by driving with a "dead" foot, in other words, slowing down while going uphill and speeding up going downhill gave much better MPG than maintaining a constant speed. Yes, it's true! Should this also be true with gasoline engines? It's typical that I sometimes get, e.g., 38 MPG going downhill at 80 mph while getting 20 going uphill at 55 mph. Deadfoot driving like this can't be acheived on all terrain though. Most of the time I've had to press down or let up on the accelerator to some extent to maintain reasonable speeds. However, I do try to let my speed fluctuate as much as possible with my somewhat "dead" foot w/o aggravating other drivers too much.

I ran several tests with my Ford explorer 4.0L also. Driving the same trips at 70-75 I got around 23 MPG but when driving as slow as possible w/o getting run over (around 55) I'd get around 28 MPG. The best I ever got with my 5.0L Van was 14 MPG, but when using the "deadfoot" technique I am able to get an unbelievable 17. From my tests I do not currently believe there's a "sweet spot" or definitive speed at which a diesel gets the best MPG, not a reasonable speed anyway, however, I could believe there exists one for gasoline engines due to fact that horsepower rather increases with higher rpms in these engines while horsepower in diesels is higher at lower rpms. As a footnote, I remember my brother showing me how the best times in gasoline drag racing were acheived by running the engine up to around 6000 rpm before shifting (more horsepower at higher rpms). Is it true that the best MPG is acheived at the "best" horsepower? If so, why is this? I'd like for someone who really knows their stuff to expound on this and some of the other thoughts I've shared in my comments here. My guess is that driving slower with diesels yields a much greater difference in MPG than does driving slower with gasoline engines, but I have no idea how much and could only guess that slowing down with a diesel makes twice as much difference as with gas. I do have trouble understanding/believing something that was mentioned earlier. How can wind resistance increase at a greater rate than vehicle speed increase? It would seem to me that doubling speed would create double the resistance on the vehicle. Some really good verification/explanation on my thoughts herein with or w/o the use of some math/physics would be helpful for this layman. Robert

Robert of NC 6:01AM July 17, 2008

in response to the comment by Nancy K of TN, there are plenty of FACTS to support the fact that slower driving=gas saving.

mike of TX 4:28PM May 17, 2008

I have a 1997 Ford Explorer with 155,000 miles. It only averages 15mpg. If I could afford another car, I would. What is sad is that we are subsidizing Mexican immigrants, actually all immigrants in this country so that they can assimilate! The American marketing hucksters have sold us over the last few decades about owning a new car based on its sexiness and speed. Naturally, middle-class Americans have not known hardships such as we are experiencing today. Most have let our government run rampant just so long as they had a paycheck, a 12-pack, and an RV. That may change with the layoffs from Bear and Sterns.

I coast. Good for the brakes and less gas used!

Donna of MO 4:42PM March 17, 2008