When a company tells you that its latest development is ‘high-tech’, it means it uses the latest technology. Especially in the late 1970s, when Cadillac told you, it was, especially in those days of loyal brand loyalty. After the hot mess that was the 4-6-8 V8, and the Oldsmobile diesel disaster, GM needed a home run with its latest powerplant, the “HT4100” V8. But doomed by GM hubris and repeating some of the same mistakes that happened with the 4-6-8, the HT4100 helped nail Cadillac’s coffin for decades.
When did the Cadillac HT4100 debut?
To refresh, Cadillac debuted its new 4-6-8 V8 with the first computer-controlled cylinder shutdown in 1981. While it was a brilliant idea, computer technology couldn’t keep up with the demands of the engine. It was so bad that the automaker dropped it at the end of the year.
But that left Cadillac in a deep hole. The new HT4100 V8 was intended for the all-new 1983 front-wheel drive Cadillacs. Now development had to be cut short to reach the 1982 models. The late stages of development of new engine designs are crucial, but Cadillac had no choice.
What was the Cadillac HT4100 available in?
Cadillac’s 4.1-liter V8, codenamed LT8, would replace Cadillac’s 6.0-liter V8. It was used for both front and rear wheel platforms. And for the first year or two, it would be exclusive to GM’s flagship Cadillac brand. But there were other issues that hampered the effort, as GM’s plans kept changing.
Intended for front-wheel drive models, which were due to appear in 1983, they were delayed again and again before debuting in 1985. So for another three years, those heavier, bigger Cadillacs were now saddled with 135 horsepower LT8s. In 1985, the gas shortages of the 1970s were just a distant memory. But Cadillac buyers didn’t ask for a smaller Cadillac in 1985, but that’s another story for another time.
So every model in the Cadillac range, except for the disastrous Cimarron, got the all-new HT4100 as its standard engine. Optional was the 4.1-litre V6, and anyone who doesn’t pay attention to the previous year can still order a diesel V8. By 1985, another GM flaw, the Fleetwoods and Allante got it.
What kind of problems did the Cadillac HT4100 have?
After the cylinder actuation was eliminated, the former 4-6-8 ECU was reworked to check engine performance. The results were displayed directly on the dashboard. This was so the driver could see how much effort the small engine was having.
Almost immediately after the first sales problems started to pile up in Cadillac’s service departments. The block was a combination of aluminum blocks and iron heads, but with metal cylinder sleeves. The intake was also aluminum. But iron and aluminum expand and contract at different temperatures and at different rates.
Another GM technology problem was the use of RTV silicone instead of OG gaskets. GM was on the cusp of eliminating gaskets and had developed its RTV technology for the HT4100. But it wasn’t ready for prime time yet, which was part of the cascade of bad-to-follow.
Has the mileage improved in any case?
Weak block castings, a victim of the rush to production, resulted in head bolts pulling out and taking the threads with them. With aluminum in high-stress areas and the cylinder sleeves doing their own thing, the intake manifolds started to fail. Camshaft bearings started to eat themselves alive and the aluminum oil pumps started to fail as well. And this was all within the first month or two in the field.
Then there was the bad mileage. Because the engine had as much power as a refrigerator, drivers constantly stepped on the accelerator. With all the full throttle it takes to get these 5,000-pound behemoths out of the way, the miles piled up. But Cadillac had no choice and continued to use HT4100 gastric pumps. Surprisingly, sales rose despite the catastrophe that awaited buyers.
The final version of the engine made it into the all-new 1987 Allante Mercedes fighter two-door. But GM couldn’t leave it as it was. So it took steps to improve it and get some more horsepower.
How was the HT4100 improved, or was it?
Camshaft profiles were revised and hydraulic roller lifters replaced the straight hydraulic valve lifters. Now it got 170 horsepower. Still no rocket, but much improved over its original 135hp.
So in just a short span of time, GM had produced three of the worst production engines the world had ever seen. The 4-6-8 V8, Oldsmobile diesel and the Cadillac HT4100 set GM products on a path that culminated in bankruptcy in 2010. While some say the public has short memories, car buyers have never forgotten the domino of bad products that the General pulled out in the 1970s and 80s.
And then we haven’t even mentioned the 2.3-liter stunner he made for the all-new Chevrolet Vega, his VW beater. That’s another story for another time, too, just like GM’s X-cars starting in 1980. And there are more and more, so much so that you can’t forget them.
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