How I coaxed a VW diesel to do 80 m.p.g.

A Volkswagen diesel car won't loosen up till it's been run 6,000 to 10,000 miles, according to Gerhard Delf, VW's chief engineer for power train and emissions in the United States.

Even so, with only a few miles on the odometer of a notchback Jetta, I still managed to eke out more than 80 miles to a gallon of fuel -- 80.58 m.p.g., to be exact. It was the VW press introduction of its brand- new diesel-engine Jetta and Formula-E (for economy) Rabbit.

I hasten to add, of course, that no one really drives a car this way.

The idea was to wrings as much road distance as possible out of the car -- and coasting with the engine off was legal, to boot. A feather-light foot on the accelerator pedal, anticipating traffic lights (and hoping for a green light when you get to an intersection), a slow takeoff from a stop, and the right attitude on the part of the driver -- all of this counts.

More realistically, however, I got 67.76 miles to a gallon of fuel over a 35 -mile run by using extreme care in my driving habits but not resorting to an engine cutoff as before.

the point is, the way a motorist drives his car does indeed have an affect on how often he pulls up to the gas or diesel pump.

Mileage-conscious VW now is talking about a 3-cylinder, 75-m.p.g. car by the mid-1980's but right now the Formula-E Rabbit is the best it can do here. Some 2,000 cars are being consumer-tested in three cities: Houston; Pittsburgh; and Phoenix Ariz., before the shift-light system is sold nationwide.

Too, the Environmental Protection Agency has been debating the merits of the shift-point light for the past year and still has not made its decision on whether to allow VW to advertise it as an economy tool.

"We don't ask anyone to slow down his vehicle for fuel economy," Mr. Delf asserts. Rather, he adds, it shows how to reduce fuel usage while maintaining the same power from the engine.

The fuel-conscious motorist will never see the electronically controlled light, anyhow, because he will upshift before the light is programmed to come on.

In the 130-mile, four-leg fuel-economy run a short while ago, I don't remember ever seeing the amber fuel-economy light. Like a spare tire, perhaps, it's there if you need it -- that is, if you forget your high- mileage habits as the car speed picks up. Mr. Delf reports that running by the light can increase economy by as much as 7 percent, or 3 m.p.g.

The notchback VW Jetta diesel, which is about 200 pounds heavier than the Rabbit, does not have an "E" light but will zip from 0 to 5 m.p.h. in 10.4 seconds, according to Mr. Delf. Equipped with quick-start glow plugs, the engine will start in summer in from 1 to 3 seconds. At the freezing mark, it takes an average 7 seconds; while at 4 degrees below zero F., the time is 9 seconds.

The Jetta, by the way, began life without a glove box. Now it has two.

As for the Rabbit, the diesel version of the design-setting car has been the US economy champ for the past four years. Now, with the Formula-E diesel, the carmaker is trying to ensure that it doesn't lose the crown anytime soon.

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