Diesel History Retrospective: Oldsmobile’s Other Diesel

Say “Oldsmobile diesel” and most people think of the trouble-prone 350-cid (5.7 liter) V-8 that plagued GM’s full-size cars in the late 1970s and early 1980s. But there was another Oldsmobile diesel in that time frame, and it was actually a decent engine — and yet it was largely overshadowed by the bad reputation of its V-8 sister.

Introduced in 1982, the 4.3L V-6 was loosely based on the improved 1981 version of the 5.7L LF9 diesel, with which it shared many parts. Some assume that because the displacement is the same as the Chevy 4.3L gasoline V-6, the two engines are related or interchangeable. Not so, and far from it. The Olds 5.7L diesel block was based on Oldsmobile’s second-generation gas V-8 architecture with the same bore and stroke of the Olds 350 gasser. (In fact, the block is so similar to the gasser that it’s prized as a super-duty replacement block for race engines.)

The 4.3L diesel had the same bore and stroke as the 350 diesel, but the crankshaft was specially designed with 30-degree offsets between the crankshaft throws for the V-6’s “even-fire” firing order. Like the 5.7L diesel, it was naturally aspirated and used a Stanadyne DB series injection pump.

While the 5.7-liter V-8 suffered from some rather serious teething problems when first introduced (rushed to production, it was a sound design that was weakened by cost cutting and poor execution), the truth is that most of the issues were rather short-lived, though time has embellished their severity. GM owned the diesel car market in the 1980s; in 1981 alone, they sold 310,000 diesel cars, which was 60 percent of the diesel car market. GM had already addressed many of the 350’s problems, and by the time the V-6 came along in 1982, it benefited from the General’s hard-won experience.

One of the biggest problems with the 350 diesels was water in the fuel ruining the injection pump and injectors. The 4.3L was protected with a water separator as well as a better fuel filter. Another major problem for the 350 were the weak torque-to-yield (TTY) head bolts and too few of them. The 4.3L still used TTY bolts (albeit better ones) but had six bolts per cylinder rather than four. Other 350 issues, including main cap bolts that were too short and an improperly balanced crankshaft, were rookie problems not repeated by the 4.3’s engineers.

The 4.3L came in two versions. The LT6 was an all-iron engine designed for the rear-drive G-body cars (Buick Regal, Chevy Malibu and Monte Carlo, Olds Cutlass Supreme and Cutlass Calais), while the LT7 was designed for front-wheel-drive cars like the Oldsmobile Cutlass Ciera. The engines were significantly different, with the front-drive LT7 engine employing aluminum heads and a low-profile die-cast aluminum intake manifold. As a result, the LT7 was 62 lbs lighter than the LT6. The LT7 also had a serpentine belt system, so the accessory mountings were very much different that the rear-drive engine.

Smaller differences included different blocks, with the front-drive version weighing 11 lbs. less and being a little more compact. Both engines used roller tappets, the same ones used in the 5.7, the later 6.2 diesel and even Ford’s 6.9. The crankshaft was nodular iron, with four main bearings and rolled fillets. The pistons were autothermic with a cast iron top ring groove protector and a full floating pin. The top ring was barrel-shaped and moly-coated.

The 4.3L was innovative and an engine with several firsts or near firsts. It was the first mass-produced V-6 diesel designed solely for passenger car use and only the third road-going V-6 diesel offered in the American market. It followed the medium-duty GM V-6 Toro-Flo truck diesel (the smallest of which was 351 cid and the biggest 478 cid) of the early 1960s and the 426-cid 6V71 of the late 1950s. There were a few other V-6 diesels going back to the 1940s and 1950s, including a few big stationary, rail or marine units from GM and a couple of low-volume truck engines from Europe. There are quite a number of V-6 diesels today, including the popular VM unit now appearing in Ram half-tons.

The 4.3L was also one of the first diesels with an aluminum head. At the time it was built, the only commonly seen aluminum-head diesel here was the Volkswagen Rabbit’s 1.5L four-cylinder, which had debuted just a few years earlier. Mercedes followed shortly with an aluminum head diesel in 1986. GM claimed the aluminum heads on the transverse 4.3L were the first high-volume application of the lost foam casting process. A polystyrene pattern was made and then surrounded by fluidized sand. Molten aluminum was then poured into the mold, which vaporized the foam. The heads were successful in the short term and have proved long lasting; cracked heads on the 4.3L are not unknown but like most aluminum heads, failures are usually related to overheating or poor maintenance. In the case of the 4.3L, the cast iron heads from the LT6 are a direct replacement.

Power output was the same for both front- and rear-drive versions: 85 hp at 3,600 rpm and 165 lb-ft of torque at 1,600 rpm. Though the numbers are modest, the engines actually delivered reasonable performance in the under-3,000-lb front-drive cars. (The heavier rear-drive cars were anemic by comparison.) The EPA rated the 1983 Oldsmobile Cutlass Ciera diesel for 28 mpg city, 41 highway and 33 combined. Converted to the modern rating system, that would be 24 city, 39 highway and 31 combined.

In 1983, Olds engineers modified a Cutlass Ciera coupe as a sporty concept car. Calling it the Tuned Induction Diesel, it featured a specially designed intake manifold, updated injection pump and free-flow exhaust. The new intake used Helmholtz tuning, which involves finding the perfect length and diameter intake runner. In this case, the runners were much longer than stock and attached to dual plenums. The increased airflow allowed a larger fuel shot, and output jumped to 101 hp and torque to 180 lb-ft. The extra grunt provided a 10-second 0-60 time and a 17.5-second quarter-mile at 77.2 mph (both with a five-speed manual not available in the standard Olds cars). A few period magazines covered the car and the Olds engineers were quick to point out the intake tuning was cheaper than a turbo, albeit with more limited gains. Had the diesels remained popular, some version of this concept engine would likely have appeared in production.

By the mid-1980s it was clear that diesels weren’t going to remain as popular as GM had hoped, so they phased out all of their diesel cars after the end of the 1985 model year—just as all the bugs had been worked out. Had they been more popular, GM’s diesel cars could have continued to evolve into sleek, fast, Mercedes-like fuel-sippers, although some argue that had the engines been more evolved from the start, they might have been more popular. A common thought is, “What if GM had turbocharged the engines?” That would have been great but would have added significantly to the cost, and while we diesel enthusiasts might have been willing to pay a premium, GM decided that the general car buying public wouldn’t. Put it into the automotive “woulda, coulda, shoulda” file. DW

The mid-size Oldsmobile Cutlass Ciera made its debut in 1982, sharing GM’s new A-body front-wheel-drive platform with the Chevrolet Celebrity, Buick Century and Pontiac 6000. Engine choices for the A-bodies were a base 2.5-liter gasoline four, a 3.0L gasser V-6, and a new 4.3L (261-cid) V-6 diesel.

The Cutlass Ciera was Olds’ best selling model for most of its 1982-1996 run. The diesel was an option on 1982-1982 Cieras, and it came exclusively with a TH125C three-speed automatic transaxle with a lockup torque converter, this despite the fact that a four-speed auto was soon introduced for the gassers and Chevy offered a diesel Celebrity with a five-speed manual.

The Cutlass Ciera came as a two-door coupe or a four-door sedan. The base Cutlass Ciera LS was nicely appointed but the Brougham model gave it a little more of that “Big Daddy Caddy” feel, while the ES had more of a youthful, sporty look. Most of the major options were a la carte and included six-way power seats, sunroof, power locks, tilt steering wheel, four-season A/C, and many other luxury goodies.