Jan 29

Gas Mileage Primer : Part 2

Photo credit to Dave Catchpole

Times are hard. Money is tight. Today we show you how to to get more miles out of your tank with maintenance and modifications on your daily driver.

Now that you have a sipper, I’ll get to the maintenance and mods to extend the range. Number one on the list is tires. For best milage, make sure they are properly inflated. I start with the car manufacturer’s recommended pressures. I then drive the car for 50-100 miles and check the wear. What I’m looking at is how far off the shoulder the wear is happening. This is depending on how hard your driving the corners. I feel that around half the radius of the shoulder with normal driving and about two thirds with spirited cornering. Another thing is the alignment. If it is off, the dragging of the tires is a waste of gas as well as wear on them.

Now is the time to check the fluids in your car. Make sure that they are all topped off. But here’s a tip that you won’t hear from anyone else. If you keep a 3K mile oil change, it’s okay to run the oil around a half a quart low. My gauge is the middle of the fill mark on the dipstick. So why? It’s to keep the crankshaft out of the oil in the pan, which can cause a loss in engine efficiency. With a well kept maintenance schedule it is not bad to run it a bit low. It is certainly better than running too much oil. I should say that a switch to synthetic lubricants should give better efficiency, but I’m not exactly sold on it either. I have run synthetics in my main car, but I haven’t documented gain or losses with a switch from conventional fluids. This sounds like a future tech article, once I get a reliable test mule. I have heard of another fluid mod for mileage gains, but I strongly advise against it. I have heard of people recommend using a thinner grade engine oil. This is a catastrophy waiting to happen. Always use the manufacturers recommended grade oil. The engine’s clearances are specifically engineered for just that grade oil. Changing to a thinner grade will not only increase premature wear, but cause failure.

For highway heavy commuters, keep the car washed and waxed. I realize that it is a drag is a small part of the mileage puzzle, but every little bit helps right. I once read an article where Fed Ex had gained 3% fuel mileage on their air fleet. With how many planes they keep up in the air, it equalled a savings in hundreds of thousands of dollars for them. Now I understand that 65 mph is worlds away from 500 knots but like I said, every bit can help out.

My theory on modifing for mileage is to increase efficiency. Mostly on the exit side of the engine. From my experience, a free flowing exhaust is worth at least a couple of MPG. Some people believe in keep a clean air filter. While it’s a good idea for a carburated car, I’m not sold on that for injected cars. From my experience, a free flowing replacement actually made my mileage worse. Another good tip is my tire size. Now for hyper-milers you want as skinny a tire as you can get. I go the other way slightly. I order my tires with one size wider with the other numbers the same. If the stock size was 245/45/17, I go to a 255/45/17. This gives you a slightly taller tire. It effectively raises your gear ratio and will make your speedo wrong. But I have a trick for that as well. For your newer cars you can recalibrate the computer for the new size. I have all cars with gear driven speedometer. I have a marked mile that I check the distance on the odometer and then figure out the adjusted speed. So if I drove the mile and it came up .95 on the odometer I know that the car will gain one mph for every 20 mph of speed. So 60 is really 63. .9 would gain 1 per 10 mph and so on.

Now I’m not suggesting wagon wheels and rubber band tires. I feel that the ridiculous wheel sizes are not only ugly, but down right dangerous in a otherwise stock vehicle. These huge sizes take the drivetrain out of its optimum gear ratio. That makes pulling away from a stop a more throttle heavy event. As an added detriment, the new wheel package will effectively triple or more the stock wheel weight. Which is never good for efficiency. I like a lighter weight peformance based wheel. But you must do wise shopping. There are tons of “performance” wheels that are much weaker than the stock alloys. And the wagon wheels are extremely dicey on overworn streets. My general rule is to look at grassroots racing events. Notice what wheels are most used. Ask around the various competitors for what brands and models are go to, and avoid at all costs. One form of motorsports that stands out to me is drifting. They absolutely torture the wheels, so they must be strong. And it is hugely visually based, so the wheels they use are generally good looking.

I did mention gear ratio a slight bit in the tire size part, but gear ratios are really key to maximizing the package. This is mainly looking at pre 1980’s cars. Most cars from the last 30 years are generally optimized for highway mileage due to the lessons of the ’70 gas crisises. But whether ordered will a performance gear, or modified to one, some older cars can benefit from a (numerically lower) higher gear ratio. Now I’m not telling an owner of an unrestored Boss 429 or L96 SS Chevelle to take change their gear ratio for mileage. Because if you can afford that kind of car, you’re not worried about pinching pennies on your fuel bill. I’m talking about the owner that could get something more modern, but is infinitely too hipster to drive something beige. Kind of like our own RenoWrench.

A higher gear ratio will help out an older car gain some extra use by making it more efficient. But the real deal is retrofitting a modern overdrive transmission into your ’60s street machine. By the ’60s all of the Big Three have had the beginnings of the small block engines that would serve them on into the ’80s. Most of them are direct bolt ins behind most small blocks from this era. Not to be forgotten but some of the last vesions of the big block families were available in trucks with an overdrive transmissions. But finding them can be difficult compared to a T-5, AOD, or 700R4 that was behind any 350 GM or 5.0 Ford.

So that’s about it for mods. If you have any more suggestions for ways to cut down the fuel bill, leave a leave a line in the comments. Next time I’m going over how to operate the car for maximum mileage.