What I thought might be instructive is to take one vehicle (my pickup is the guinea pig) and see what can be done to gain as much fuel economy benefit as possible. With that in mind, lets get started.

Engine Oil

My owners manual recommends SAE 5W-30 for year-round use. However, I wondered if something would give me a bit more fuel economy. To that end, I spoke with Bob Olree, development engineer, materials engineering for fuels and lubricants at General Motors Powertrain in Troy, Mich., about using lower-viscosity engine oils. Olree pointed out that my owners manual also recommends SAE 0W-30 for colder climates. When specifically asked about SAE 0W-20, he would not recommend that grade for my truck – but he did indicate that he has confidence in the quality of modern engine oils. (I should note here that Olree took me to task in a Letter to the Editor in Julys issue for my concerns about wear protection with SAE 0W-20.)

Reading between the lines, I think that I could use SAE 0W-20 and not put my engine at significant additional risk. Changing from SAE 5W-30 to SAE 0W-20 should net me an additional 0.5 percent in fuel economy. Thats worth an additional one-tenth of a mile per gallon at my current estimated 20 mpg. Maybe Ill try it next winter.

Transmission Fluid

Automatic transmission fluids have been very low viscosity, friction-modified fluids for some time. While there are diverse and incremental changes going on in the ATF area, no one has quoted any fuel economy benefits from the fluid alone. There are some rumors circulating that improvements in fuel economy might be able to be captured with advanced ATF chemistry. Transmission hardware designs are changing to provide better fuel economy, so think continuously variable transmissions (CVT) or double-clutch designs for your next purchase.

If you have a manual transmission you can possibly use a lower viscosity lubricant. One recommendation is for an SAE 75W-85 synthetic product meeting the API GL-4 specification. It may be possible to go to an SAE 70W-85 and perhaps capture a miniscule amount of additional fuel savings. Many manual transmissions are using ATF too, which is probably going to give maximum benefits for fuel economy. However, before making that change, read on about gear lubricants.

Rear-axle Lubricants

The recommended axle lubricant for my truck is SAE 75W-90 synthetic gear oil meeting GM Specification 9986115. I wondered if I could gain from a gear lube of lower viscosity (SAE 75W-85) with improved chemistry. Remembering that Lubrizol had worked on fuel-economy-enhancing gear oils back in the 1980s, I contacted Paul Lewis, the companys global automotive gear oil additive product line manager, in Wickliffe, Ohio. I asked whether or not any new work had been done to enhance fuel economy via gear lubes.

Lewis and I discussed an article on Lubrizols website about automotive gear oils that raises A Question of Balance. It points out the basic conflict between fuel economy benefits that could be gained by going to lower viscosities versus the necessity of maintaining and enhancing the fluids impact on durability. It is not difficult to claim axle efficiencies can be improved by reducing viscosity to minimize frictional churning losses. However, light trucks and SUVs are often used in conditions that result in high loads and high operating temperatures. In addition, engine horsepower has increased by 34 percent over the last decade, while axle sizes have remained constant. Sump capacities have been reduced and drain intervals lengthened.

The bottom line seems to be that it has taken new additive technologies to maintain and enhance gear durability, while lowering the viscosity of the axle lubricant for improved fuel economy.

Lewis pointed out that the durability vs. fuel economy question is one that is of great interest to original equipment manufacturers. He also pointed out that the industry is very interested in developing a standardized fuel economy test for gear oils. Currently, the various OEMs have data and procedures they use to characterize the fuel economy benefits to be gained from gear lubricants. Recently however, the U.S. military approached SAE with a request to develop such a test in conjunction with SAE J2360, which is the SAE standard for automotive gear oils (formerly MIL-L-2105E). Although its in the early stages of development, any standard will likely cover fuel economy for both passenger cars and commercial vehicles.

As far as improving my fuel economy by using a lower viscosity gear lube in my truck, it sounds as though the benefits are not really measurable and the risks are too great to take a chance at this time.

Change More than Oil

As I was writing this article, GMC e-mailed its Top 10 fuel saving tactics to me. Just in case you missed it, they are as follows:

1. Go the speed limit. Use cruise control.

2. Drive evenly. Avoid hard stops.

3. Avoid idling and rush-hour traffic.

4. Open windows at slow speeds. Use air conditioning on highways.

5. Remove junk from the trunk.

6. Fill up when its cool and before holidays.

7. Dont top off gasoline and tighten the cap.

8. Use the correct fuel grade.

9. Dont accelerate uphill.

10. Avoid rooftop carriers.

For most of us, its hard to avoid rush-hour traffic. As far as driving habits are concerned (e.g., speed and road practices), most of us grew up driving in better times when go, go, go was the norm. It seemed as though we were always in a hurry to get someplace. That hasnt changed very much. In my case, it has required a great deal of retraining and Im still learning.

Where I live in Arizona, opening the windows in lieu of air conditioning is not a good idea in the summer! Filling up when its cool is also difficult in these parts. In fact, there has been a lot of discussion locally about what should be the standard temperature for weight-to-volume conversions for fuel. As most of you know, 60 degrees F is the temperature selected a number of years ago as representative of the average temperature across the United States. Here in the Phoenix area, 60 F is probably a bit low in the summer, but in the winter, it is an advantage to the consumer. However, thats a subject for another article.

Some of GMCs supplemental recommendations are to change your oil to the recommended grade, make sure your fuel system is clean and functioning properly, inflate your tires and keep them at the proper pressure, etc. There are literally dozens of other suggestions for maximizing fuel economy, and I recommend that anyone who is interested just surf the web to see whats out there. (Just remember to be skeptical about what you read.)

Stopping Losses

One area of interest is the amount of energy lost between the fuel coming in and the vehicle moving down the road. The EPA has detailed the various factors relating to energy losses – from the engine to the driveline and over the road – for vehicles in urban and highway modes. (See chart on page 8.)

What is so amazing about this analysis is the variety and magnitude of energy losses that occur. No wonder the automakers go nuts trying to squeeze every bit of fuel economy out of their fleets.

In the case of my truck, I have never seriously considered investing in a bed cover. After seeing that there is an 11 percent loss in efficiency due to aerodynamics at highway speeds, I am now shopping for something to streamline the air flow over the vehicle. Even a snap-on tarp could help. In fact, taking the tailgate off will help by allowing for smoother air-flow over the trucks body. Im not sure I can calculate the impact of this aerodynamic fix but assuming that half of my driving is urban and half is highway, the average impact of aerodynamic losses would appear to be 5.5 percent. If I can cut that in half by covering the truck bed, I could perhaps capture 2 percent or 3 percent improved fuel economy. Thats about 0.5 mpg, or another 12 miles per tank full. Not much, but it is a step in the right direction, and five times what Ill gain from a lower-viscosity engine oil.

Some of you regular readers are probably saying about now, What happened to Steves view that such small changes will never be detected by the average driver? I guess that even an old curmudgeon like me can see the light.

Gidgets and Gadgets

No discussion of fuel economy would be complete without mentioning the many (and I do mean many) devices that are offered to save gasoline. They can be grouped as either fuel-mixing or fuel-modifying devices. Some purport to improve the mixing of fuel and air by creating turbulence in the intake manifold. Some claim to align the fuel molecules for more complete combustion. Other devices claim to convert water to hydrogen and others use platinum in a water solution to catalyze combustion.

The EPA has looked at over 100 of these devices and has found that none of them deliver on their promise of improved fuel economy. Popular Mechanics tested a number of these devices and got results similar to the EPA findings.

So the bottom line to fuel economy is to follow a few guidelines:

1. Maintain your vehicle.

2. Make sure you use

the right lubricants for all parts of the vehicle.

3. Use good driving practices.

4. Dont bite on claims of great improvements in fuel economy by using add-on devices.

Drive safely and economically.