Plastics graduate underhood.

When Dustin Hoffman was told in the 1967 movie The Graduate that plastics were the future, not even the forward-thinking screenwriter could have known that 30 years later plastics would show up in as many places under the hood as they do today.

Although the development of underhood plastics began five years before Mr. Hoffman and Simon & Garfunkel made Mrs. Robinson famous, plastics suppliers and molders still have a sales job to do when introducing new applications for an engine-compartment components.

"With each application, people's confidence in nylon's ability to survive grows," says Mark Schuchardt, a technical specialist at DuPont Automotive, who adds that today's engines are actually easier on plastics than earlier powerplants. Nylon melts at 500[degrees]F. "Engines are more efficient now, and therefore give off less radiant heat."

Molding plastic into one part replacing several metal pieces and the weight savings associated with plastics are the principal drivers in bringing more plastics under the hood. Other benefits include lower assembly costs and a reduction in manufacturing cost, because there is rarely any machining or painting necessary.

Plastics started appearing under hoods as fan shrouds and liquid reservoirs in the late '70s. It wasn't until the late '80s that they became sufficiently heat-resistant to be placed directly on the engine.

Since then there has been a proliferation of underhood plastic components. Underhood applications for nylon -- including air-intake manifolds, valve covers, windage trays (a baffle between the oil and the crankshaft) and throttle bodies -- are expected to consume 201.6 million lbs. (92 million kg) of the material by 2005. Total underhood use of nylon was 117.4 million lbs. (53 million kg) in 1995.

North American growth follows gains in Europe. Neither the U.S. nor Canada had a commercial application of nylon for intake manifolds or valve covers in 1990, yet in Europe, 1.1 million lbs. (500 t) were used for manifolds and 400,000 lbs. (180 t) went into valve covers that year.

AI Winterman, director of BASF Automotive Materials, agrees with DuPont's Mr. Schuchardt on the issue of plastic manifolds.

"Beginning with some late '97 models and carrying through into several '98 models, there will be a major swing to nylon air-intake manifolds for U.S.-made automobiles," he says. "What's more, there likely will be new manufacturing technology in the year 2000 that will further enhance the growth prospects for nylon powertrain components."

Nearly all of the nylon air-intake manifolds on engines for '97 and '98 will be made using the lost-core injection-molding technique, Mr. Winterman explains. "However, welded air-intake manifolds will begin making some inroads, probably on '99 models." He notes that welded manifolds, which are less capital-intensive to make, already are making strides in Europe.

"In early '95, we said that by the end of this decade over 50 million lbs. (22,700 t) of glass-fiber reinforced nylon would be used worldwide to make air-intake manifolds and that the U.S. automotive industry would account for 50% of this amount," says Mr. Winterman. "It now looks like this was a fairly conservative forecast. We see the possibility for over 100 million lbs. (45,000 t) of glass-fiber reinforced nylon being used to make these parts by the year 2000."

DuPont says it expects valve cover applications to grow to 10 million lbs. (4,500 t) by 2005 and windage tray applications to grow to 5 million lbs. (2,300 t) by 2005.

Nissan's Sentra has the only current thermoplastic valve cover for the U.S. market. It's made of DuPont Minlon 22C nylon resin.

Other notable underhood components on vehicles today include:

* Cylinder-head covers for BMW's latest generation of 6-cyl. inline 2- to 2.8L engines (DuPont Minlon PA 66);

* Valve covers for Porsche's Carrera 911 (DuPont Zytel nylon 6,6);

* Oil pan gaskets with integrated windage trays on GM's 3800 Series II V6 engine (Zytel);

* Engine covers for the Ford F Series pickup (Hoechst Celanese Impet, a recycled polyester);

* A two-piece thermostat housing for Ford's 3L, 24-valve, 6-cyl. Duratec engine (Hoechst Celanese Fortron polyphenylene sulfide [PPS]). It replaces nine metal parts, including six screws and a bracket;

* Internal accumulator pistons for GM's 4L60E transmission (Fortron);

* A single-component clean-air duct for Neon and Dodge Dakota (Advanced Elastomer Systems' Santoprene thermoplastic rubber), replacing multiple-piece air duct assemblies.

Although not located under the hood, plastic fuel tanks are making major gains in the North American market, says Michael Klamm, BASF Corp.'s manager for Lupolen high-density polyethylene (HDPE) resin. "Blow-molded polyethylene fuel tanks are entering a period of very rapid growth in the American automobile industry," says Mr. Klamm "Prior to 1996 about 30% to 35% of American cars had fuel tanks made of HDPE, compared with about 70% to 75% of European cars. By the end of the decade, the use of HDPE likely will double to over 60% (in North America)."

It's often said that art imitates life. In the case of The Graduate, art predicted life.