9 November 2005

Increasing Your MPC (Miles Per Collector)

Back when gas was $1.50 a gallon, it cost about $33 (for one tank of gas) to drive on our car club’s annual “Fall Color Tour.” This year it cost $68.64. When the numbers on the gas pump ring higher than $50, it’s time to review ways to save gas through a combination of better maintenance and careful driving habits.


We know that a well-maintained, efficient car will get better gas mileage. A tune-up provides peak efficiency. Doing a tune-up involves replacing spark plugs, breaker points, rotor, condenser, distributor cap and spark plug wires with new parts, and setting the ignition timing and carburetor.

New spark plugs might not save gas by themselves. You must use correct plugs and set the air gap correctly. In a test conducted in Florida , a car with its plugs gapped 0.02 inches “tight” got 20.75 mpg instead of the 25.75 mpg it averaged with a correct gap – a 19 percent decrease. When the plugs in the car were gapped 0.02 inches too wide, it got 19.25 mpg – a 25 percent decrease! To work best, spark plugs should also have new gaskets and be torqued properly.

In many older collector cars, the breaker points, rotor and condenser in the distributor help high-voltage electricity generated by the coil reach the spark plugs at a precise moment. If you want these parts to work at maximum efficiency, they should be in good or new condition. However, that isn’t enough. Quality counts too. Some reproduction ignition parts being sold today aren’t as good as original equipment manufacturer (OEM) parts. When you hold repro parts next to OEM quality, you can see their lighter construction. If you want maximum mpg, get OEM or top-quality aftermarket parts. It makes a difference.

If your car has electronic ignition, you won’t have to worry about replacing the points, condenser and rotor. An electronic ignition is, by design, more fuel-efficient than a points system. Many old cars can be converted to electronic ignition, and you may want to check advertisements in hobby publications to see if PerTronix or another company makes a system for your car.

Whether you have points or an electronic spark, your vintage car will have a distributor cap. It must be free of cracks that let high-voltage electricity leak out of the system. Here, too, it’s important to get OEM quality parts. If you install look-alike parts from overseas, you may find the car won’t even run. (I did this.)

Spark plug wires also conduct high-voltage electricity. Only clean, correct, top-quality wires will boost fuel economy. You can test old wires by operating the car in a dark place and cracking the hood open. If you see flashes of bluish-white light, your spark plug wires are leaking. Before tossing them, check if the boots and connections fit tight on the coil tower, the distributor towers and the spark plugs. They might just be loose.

To make sure the electricity flowing through the system reaches each spark plug at the precise moment the fuel-and-air charge should be ignited requires the ignition system to be “timed” properly. This is done by using a strobe light to highlight a timing mark that indicates when the spark plug in the No. 1 cylinder is firing. In the case of the car tested in Florida, it was discovered that retarding the timing by 6 degrees lowered fuel economy 14 percent from average, while advancing the timing 6 degrees lowered gas mileage from 25.75 mpg to 21 mpg – an 18 percent decrease.

If your collector car has a carburetor (most do) adjusting this air/fuel mixing device is extremely important. An overly rich mixture contains too much gas and can kill fuel economy. A second adjustment on the carburetor sets the idle speed. On the Florida test car, researchers discovered that a 50-rpm increase in idle speed lowered average fuel mileage two percent to 24.50 mpg.

Check the vacuum fuel pump on your collector car for signs of leakage. Some modern gasoline will eat through old diaphragm material. In addition to wasting gas, a leaky fuel pump is dangerous. Get a rebuilt pump or a pump rebuilding kit with modern diaphragm material that’s unaffected by today’s gas.

A clean air filter is important for good fuel economy. Some collector cars use take-apart air filters that you clean in kerosene. Some have to be re-oiled. By the mid-’50s, manufacturers turned towards air filters with replaceable elements. A dirty or clogged air cleaner makes the air/fuel mixture richer. The Florida test car had a two percent decrease in mpg with a partly-clogged air filter.

If your collector car has vacuum–operated windshield wipers, you might have noticed the wipers slow up or stop as you step on the gas to climb a hill. Changes in the amount of pressure that vacuum hoses “pull” can also affect the efficient operation of an engine. The newer the car, the more vacuum hoses it probably has. When the testers in Florida disconnected one vacuum hose from their car’s engine, its fuel efficiency dropped eight percent to 23.75 mpg.

The correct amount of air in your tires and proper wheel alignment decrease road resistance and increase fuel economy. Check tire pressure each time you drive. Tubeless tires arrived around 1955. If you’re using tubeless tires on a car with non-tubeless rims, you may get slow leaks. If your car has porous aluminum rims, they may also leak a little. Rotate your tires, and check and reset your wheel alignment. In the test in Florida , tire pressure was decreased 8 psi over factory specs and fuel economy fell 1.5 percent. However, when tire pressure was increased 4 psi, fuel mileage went up three percent.

A bad muffler can be another gas robber. The dirty, damaged or clogged muffler builds up excessive backpressure and every psi of backpressure robs about two percent of the car’s power. Fuel use climbs about three percent for every psi and about five percent for every 1.25 psi.

Good Driving Habits

Good driving habits are as important to good fuel economy as proper maintenance. Fifty years ago, Popular Science magazine said, “Auto designers are putting some fancy engineering into making your engine run more miles on less gasoline, but there’s one vital part they can’t redesign – you. And often it’s this part behind the steering wheel that wastes gas.” Since then, Detroit automakers have drastically increased mpg, but drivers seem to have gone the other way.

Fast driving guzzles gas like nothing else. Two stick-shift 1955 test cars got 19-21.5 mpg at 40 mph, 16-17 mpg at 60 mph and 11 mpg at 80 mph. Conversely, dropping their highway cruising speed from 60 to 50 mph saved 12 percent on gas. Remember that 12 percent when driving to the next car show.

Shift properly. Jet-like getaways will cost you fuel. Accelerating at wide open throttle uses more gas than part-throttle acceleration. Fuel consumption is highest in low gear and lowest in high gear. Shifting into the highest gear as soon as possible, without lugging the engine, ups mpg. On cars with automatic, stay out of lower gears and avoid using the “kick-down” gear to accelerate fast.

Careless choking can send you to the gas pump without passing “Go.” If a hand choke is pulled out more than ¼-inch – 15 percent – you lose money. With its choke out 40 percent of the way, a typical mid-‘50s six will give you about 8 mpg compared to 21.5 mpg with the choke all the way in. A defective automatic choke could cause a similar loss. Use the hand choke as little as possible.

In old cars, cold engines were real gas burners. A typical 1955 car had to drive five miles before it got warmed up. If the same car was left outside overnight, it had to go 10 miles before it was warm and that took 15 percent more gas. Using an engine heater before leaving for the car show will save you gas.

If your car has overdrive, use it. With overdrive gearing, your engine speed goes down and you save gas. A big six-cylinder Nash-Healey with overdrive followed a four-cylinder MG TD 120 miles home from a show. The Nash-Healey got better mpg, because its engine was running at half the rpms.

Stopping a car like a cowboy stops a buckin’ bronco wastes fuel by using the car’s energy to heat brake linings and tires. When one test driver jammed on the brakes at 40 mph, he used over twice as much gas as another test driver who coasted from 40 mph to 20 mph and then braked to a gentle stop.

Planning your route ahead of time can save gas. By thinking about the red light ahead, you can plan to coast to a stop. Use a car’s momentum to get you further along. If you know that a big hill is coming, speed up gradually before you start uphill. Naturally, taking the shortest-distance route will use the least gas.

John “Gunner” Gunnell is the automotive books editor at Krause Publications in Iola , Wis. , and former editor of Old Cars Weekly and Old Cars Price Guide.


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