General Motors’ High Technology Engine, and Other CAFE Foibles (Part IV)


We return to the saga of GM’s High Technology engine today, after taking a diesel detour in our last entry. Concurrent in the High Technology engine’s timeline, the Oldsmobile diesel’s failure was quick, but certainly not painless. It put the majority of American consumers off the idea of a passenger car equipped with a diesel engine. And by the time GM pulled the diesel from its various brand lineups, there was a strategy change over in HT4100 land: Not calling the engine HT anymore.

Though the engine was full of designed-in mechanical issues and failures, cars with the Cadillac-exclusive HT4100 sold well. It was the days when American buyers were loyal to domestic offerings, and usually loyal to one brand in particular. Even through a swap to front-wheel drive, downsizing, poor quality, and styling that was lacking in 1985 terms, Cadillac sales increased. The brand sold around 300,000 cars each year from 1983 through 1986, riding on a wave of consumer loyalty built in the Sixties and early Seventies. For a modern times sales reference, Cadillac sold 156,246 cars in the Most Recent Normal Year, 2019.

Even though buyers weren’t put off by the HT branding, Cadillac’s marketing people were eager to get away from it. Sales fell by around 14 percent in 1987, a drop to 261,284. Keep in mind, even with HT and diesel woes, Cadillac was still trouncing Lincoln’s 1987 sales figure of 166,037. HT4100 disappeared from all Cadillacs after 1987, save for the Allante with its special high-powered version which lasted through 1988.  For all other cars, the ’88 model year introduced a new power plant for Cadillac Style, the 4.5.

The 4.5 was in fact an enlarged and improved version of the HT4100 but was never referred to as an HT4500. At 273 cubic inches, the “new” 4.5-liter offered a modest power increase over the 4.1, at 155 horsepower versus the 135 horses of its older sibling. More carefully engineered than before, Cadillac knew a rushed repeat of the HT4100 wouldn’t cut it. Compression on the 4.5 was higher than on the HT at 9:5:1, and premium fuel became a requirement.

Carried over from the 4100 were the throttle body fuel injection system, as well as the aluminum block and cast iron head combination. This meant that the cooling system still required regular and careful maintenance. Intake and head gasket failure were still factors in the 4.5, ideally mitigated through regular coolant changes and the addition of GM’s cooling system sealant tablets.

The tablets were (are) manufactured by AC Delco, and were meant to correct leaks that already occurred, and prevent leaks in the future. Said leaks were caused by the aluminum block and coolant components becoming porous over time, which isn’t the best outcome for critical car components.

Sales improved in 1988, up slightly to 266,548 cars. Cadillac sold the 4.5-liter engine for a shorter time than the HT4100, as it continued to develop the series after the 4.5 went on sale. DeVille, Seville, Eldorado, and Fleetwood models between 1988 and 1990 used the 4.5-liter. Sales in 1989 remained steady at 266,899 cars and dropped in 1990 to 213,238.

The Allante joined the 4.5 fold in 1989, and once again received its own special version of the engine. Called the LW2, the Allante’s 4.5 implemented the ever-important multiport fuel injection. The modern fuel system upped the power to 200 horses, but only for the LW2. Given the Allante’s flagship status and outlandish asking price ($57,183, or $132,757 adjusted), it was important that it received new technology first.

Multiport was added to the standard versions of the 4.5 for 1990, where it meant 180 horses and 245 lb-ft of torque. Huge “4.5 PORT FUEL INJECTION V8” badges were emblazoned on the back of every Cadillac on the lot. Unlike the HT4100, all applications of the 4.5 were front-drive as Cadillac shifted from its prior rear-drive identity, and chased after the “younger European car buyer” General Motors was so obsessed with between 1986 and about 1998.

Cadillac was ready with its final iteration of the HT for the 1991 model year. The 4.5 was upsized again and became the L26 of 4.9 liters. Horsepower and torque both increased with the 4.9, up to 200 horsepower, and 275 lb-ft of torque at 4,100 rpm. Never mind that this figure was attained earlier by the high-po LW2 4.5-liter, as the L26 was generously applied to the entire Cadillac lineup – apart from the Allante. Allante soldiered on with the 4.5 for 1992 and received the all-new (and not ready) 4.6-liter Northstar for its final outing in 1993.

Elsewhere in the lineup, the 4.9 remained in use through 1992 in the front-drive C-body Fleetwood, 1993 in the Eldorado, Seville and Sixty Special, and through 1995 in the DeVille. Notable in the Deville’s usage, the ’94 and ’95 models with the 4.9 were base versions, as upscale Concours used the Northstar. Guess which trims are still running today?

Despite how the 4.9 was the best engine Cadillac had used in some years, sales continued to decrease from their Eighties high. Seventeen percent fewer Cadillacs were sold in 1991 than 1990, 213,238. A slight increase in 1992 was followed by another drop in 1993 to 204,159. The HT series ushered in a damaged era at Cadillac, where the brand decided to pursue a different front-drive and Euro-centric imaginary customer that was much different from its traditionalist domestic rear-drive buyer. Cadillac lost over 100,000 annual sales from the time the HT was introduced to the time the 4.9 finished its run.

Through three generations and nine model years, the HT4100 was reworked, upsized, and generally improved to a decent reliability standard. Horror stories about the 4.9 are much scarcer than in the 4.5, and especially the 4100. The HT line would be the last engine exclusive to Cadillac for over 20 years, until the debut of the Blackwing V8 in 2018 (RIP 2020).

Unfortunately, the HT engine was a case of the fix-then-drop operating procedure that GM used so many times before. By the time the 4.9 arrived at dealers, Cadillac was already well into development of its next V8, the much-heralded Northstar 4.6. But that’s an Abandoned History for another day.

[Images: Cadillac]

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