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New Technology May Have Disadvantages

Second Of Two Parts

March 25, 1992|RALPH VARTABEDIAN

Federal fuel-efficiency laws are driving car manufacturers to cut vehicle weight every way possible, leading to new technology under the hood.

Although aluminum-block engines have been around for more than two decades, they are increasingly used by auto makers to improve fuel efficiency.

Despite manufacturers' insistence that aluminum engines are as durable as iron, doubts persist. Independent experts say aluminum engines can last more than 100,000 or 200,000 miles, but they cannot withstand abusive conditions nearly as well.

"Overheating is catastrophic to aluminum-block engines," said Bill Whitney, president of Prestige Engine Co., a Dallas firm that specializes in remanufacturing aluminum-block engines.

In the early 1980s, Cadillac introduced a series of 4.1-liter aluminum-block engines that have become a major headache, if the volume of cases in arbitration is any indication.

The engines are failing prematurely because the aluminum blocks cannot withstand overheating, which results from owner neglect and from design flaws, Whitney said. A cast-iron-block engine could probably withstand the overheating.

"Cadillac did not go to the trouble of explaining to customers the care they need to take with these engines," he said.

The failure of these engines is almost predictable. The aluminum blocks rely on oil to provide substantial cooling. The oil is pumped through a special section of the radiator to cool before it is pumped through the engine.

If the engine overheats, the oil loses its viscosity and the pressure drops below what the engine can tolerate. GM specified that the engine requires eight pounds per square inch of pressure, but the dashboard warning light does not activate until the pressure drops to about four pounds per square inch, Whitney said. He provided GM specification charts to back up his claim.

The oil pressure is not adequate to lubricate the top of the engine, leading to camshaft failure. Since the oil flows from the rear to the front of the engines, the camshafts almost always fail first in the front.

None of this would matter if the engine didn't overheat, right? But unfortunately, the Cadillac engine, like all engines, tends to lose coolant over time. Radiator caps lose their ability to hold in pressure. The coolant spills into the overflow tank and it eventually overflows too.

This would not be a big deal, either, except for a problem in the heat sensor that warns the driver of overheating. The sensor is positioned so that it loses contact with the coolant if the coolant level drops, Whitney said.

So, the radiator cap fails, which allows the coolant to leak, which causes the engine to overheat, which thins the oil, which ruins the camshaft. As this happens, the motorist has no idea of any problem, because the warning systems have some flaws.

The problem began in 1982 Cadillac engines. By 1985 the problems had been remedied.

Whitney drives an aluminum-block Cadillac and says he has no problems with it. Other experts note that iron-block engines have been thinned so much that they are also subject to problems, such as premature cracking and corrosion.

"It's possible to get 250,000 to 300,000 miles out of an aluminum block, if it's cared for properly," Whitney said.

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