The Stinker: 1978–1985 Cadillac Seville Diesel

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As the second energy crisis in a decade kidney-punched an inflation-addled nation, several automakers began to eye the diesel engine as a way to attract customers interested in high-mileage vehicles. The diesel alternative seemed especially appealing to luxury car brands such as Cadillac, whose mighty road dreadnoughts slurped fuel at unconscionable rates.

It was by no means a bad idea. Diesel engines were (and remain) in much wider use in Europe, where gas has always been more expensive and fuel economy more of a selling point. And of course, most heavy trucks in the United States burn diesel. The problem was that back in the 1970s, General Motors didn’t have any diesel engines available — or at least, none that were suited to passenger vehicle service. A GMC straight-eight diesel from a big semi would never fit into a DeVille or Seville. GM’s answer? A hasty conversion job of an already in service gasoline engine, the Oldsmobile 5.7-liter 350 V-8.

Unfortunately for the many unlucky souls who ended up getting “that great GM feeling,” the 22.5:1 compression ratio converted diesel (versus the gas engine’s 8.0:1) overstressed head gaskets, head bolts, and other critical parts never designed to handle the much greater internal stresses of diesel engines. Major service work — including complete engine replacements under warranty — became almost as commonplace as oil changes.

The new bustleback Seville, Cadillac’s “international” sedan, was the first victim to be saddled with the now-infamous diesel engine. At first it was merely a $287 option and buyers — the fortunate ones — could still get a perfectly serviceable gas-fueled V-8. But by the dread year 1980, the diesel engine became the Seville’s standard powerplant, even as word began to spread about the diesel’s propensity for spitting its bits and pieces out all over the road like teeth after a prize fight.

Even when it worked, the experience of driving a diesel Seville was not quite Cadillac. At full steam, the diesel 5.7 liter delivered all of 125 horsepower — not much to move a 4,000 pound car. And it complained bitterly each time the driver asked for a little acceleration, coughing and sputtering like a goose being hand-choked for its pate-de-foi-gras and leaving a haze of oily smoke in its wake. It idled like a high-mileage Kenworth and assaulted owners and occupants with industrial-grade stench. Making matters worse, Seville diesel owners had to stand in puddles of greasy sludge and handle oil-fouled diesel pumps at every tank-up. It was a disgusting — and financially draining — experience that poisoned the well for diesel engines in the United States. Even today, nearly 30 years after the fact, many American car buyers remain leery of modern, purpose-built diesel engines solely on account of the foul memories of the GM diesel fiasco.

Five Fast Facts

The 1978 Seville diesel was the first domestic-built diesel V-8 passenger vehicle and the last one GM ever built for the U.S. market. As of the 2004 model year, no U.S. automaker offers a diesel-powered passenger car.

Though it had a terrible record for early failure, when it ran the converted Olds diesel V-8 delivered fuel economy in the mid to high 20s — outstanding for a 4,000-pound luxury sedan at that time.

In 1980, the Seville was reconfigured to front-wheel-drive, becoming one of the first Cadillac models (in addition to Eldorado) to abandon traditional rear-wheel-drive.

In 1980, buyers could escape the diesel by selecting the “delete option” 6-liter gasoline V-8, for which they received a $266 credit applied to the cost of the car.

When the diesel engine was finally retired in 1982, it was replaced by an engine that became equally legendary for being a problem-prone, poorly engineered mess—the “HT4100” 4.1-liter gas-burning V-8.

Excerpted from “Automotive Atrocities” (MBI, 2004)

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  1. Yet another hit job on the Olds 5.7 diesel. The Olds 5.7 diesel was not a “hasty conversion job” While using the engineering of the successful Olds 350, almost every component was diesel only. I can guarantee that the author, Eric, has never owned one, never had family that owned one, and is probably not a mechanic or has mechanical talent. Simply regurgitating negative stories that we all have heard is not decent journalism. Why not seek out an owner of one today and do a in depth interview? I own and enjoy a small fleet of these diesels and continue to be impressed by the dependability, economy, smoothness, and how quiet they run. Some of the above positive comments tell more of the story.

    • Good points, Duane. Some of those engines went for hundreds of thousands of miles. I knew of a 1981 Pontiac Booneville 5.7 Diesel that had four separate owners and the engine simply wore out. It got to where it had lost enough compression that it simply wouldn’t start. A lot of the bad press surrounding this engine comes down to people not knowing how to maintain and not knowing how to drive a vehicle with one of these engines. The DX block has been a sought after block for car racers. They were solid blocks. If these engines had come with water/fuel separators, balanced crankshafts, and better cylinder head clamping power, they would have been an even better engine.

  2. Oh Jeeze, the Malibu in Caddy drag, only second worst to the Cimmaron. Fits right in with the Carter Quarter (Susan B. Ugly) and women in double-knit polyester pants-suits, barf, barf, barf.

  3. i have a 80 seville, all original survivor from florida, 74k miles. runs great. velour interior. original motor, aftermarket fuel filter/separator. 262 215 1182 make serios offer

  4. I have a 1980 Cadillac deville diesel 5.7L, I had been looking for an old Cadillac to restore for awhile as I love the cars and I was lucky enough to come across one with a diesel engine as I know not many were made (although if someone could tell me the exact number that were made diesel that would be great) this car has been insanely reliable I found, only thing I’ve had to replace in it since the safety is an alternator. And it’s amazing on fuel so I don’t mind driving it a long distance to car shows. Love my car and love when people say I didn’t know Cadillac made a diesel

  5. I still have a ’81 Coupe Deville Diesel, I have it registered as antique and drive it during summer cruise nights and shows ect. There are not to many people that even knew they made a diesel Caddy, Mine runs great and I would take it any were. I have had several 5.7 olds diesel powered cars and they weren’t as bad as people say. They were misunderstood and people didn’t know how to care for them. The worst year was the early ’78 models that had the “green Block” that wasn’t cured long enough and would distort and through off the line bore and snap the crank shaft in the D block engines. in ’81 they introduced the DX block with a roller cam and deeper main bearing bolt holes which solved most of the earlier problems with the bottom end. The big problem after that was they didn’t have a water separator and if you got water in the fuel the increased combustion pressure would cause the torque to yield head bolts to fail. With a set of head studs and a water separator installed these weren’t that bad. And just a FYI these WERE NOT converted gas engines. These blocks were cast different and had a nodular crank shaft. I have collected 5 complete engines 3 of which are Goodwrench engines since the parts availability is very limited anymore

  6. Indeed one of the worst blunders of American automotive history, but due that dubious distinction, the GM Diesels have become hot items to car collectors. While 20 years ago, the Diesel option in any GM car would cut the value in half, today it triples it or even increases it five fold. I have three of them in my collection; two of the 5.7 Diesel Cadillacs, and a Buick V6 43 Diesel (even more rare, as they were only made for two years). I would never trust any of mine to be reliable transportation, but they’re fun to take to car shows & cruise nights, and have bystanders scratch their heads and say “I didn’t see a tow truck; how’d you get it here???” Believe it or not, my ’83 Seville Diesel drew the attention of Jay Leno at the All GM Car Show in Van Nuys, CA this summer!

  7. Just to point out that a diesel Caddy (nice one) on Ebay recently elicited savage bidding. (I was gunned down on day 2). Old diesel Benzes are hot stuff on Ebay, the only hotter would be diesel cruisers from Detroit – if only there were any.

    • How much did it go for?

      In the latest issue of Hemmings there was an interesting article on formerly pariah cars from the mid-late ’70s. The featured car was (IIRC) a ’78 Buick fastback sedan with 3.8 V-6. Guy wanted around $4,500 for this ow-mileage/original and excellent condition car… I have to admit it looked appealing. No air bag, no BS – and probably a pretty nice everyday driver….!

  8. Nice article. I remember as a kid in 1981 when our neighbor bought a 1981 Seville diesel- this one with the hump-back. We always heard him coming up the street- it sounded like a truck. I think he kept that bad boy for about 9 months before he bought a Ford.

    • I miss crappy cars! I began doing reviews in the early ’90s, by which time there were very genuinely bad cars. Ugly, slow cars – sure. But outright pieces d’ sheet were fairly rare by then. Would have been to get to drive them as brand-new press cars and then do a write-up!

      • Right! This sounds like a great top 10 list; hop into the time machine and test drive most choice pieces d’ sheet:

        1. Anything that said “Quad4”
        2. Anything with “Corinthian Leather”
        3. Anything that came with some type of Levi’s jeans interior option pack
        4. Cadillac Cimarron with a manual transmission!
        5. …


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