Automotive History: Oldsmobile 5.7L Diesel V8 – GM’s Deadly Sin #34 – Premature Injeculation

Olds engineer Benner said they put together what seemed to be a proper diesel V8 and said “Let’s run it and see what falls apart first. That engine lasted about 30 minutes. So we built another, correcting the faults of the first, and ran that to see what would fall apart second, and on and on”.

That’s all good and well, if you’re going to start from scratch to reinvent the diesel. But the deadly problem is that development and durability testing was cut short, to satisfy the sales and marketing guys, as well as the bean counters. From a 1983 New York Times article:

Darrel R. Sand, a former G.M. engineer who helped design the Oldsmobile V-8 diesel engine, is not surprised. He said last week that he had strongly advised his superiors at the company against putting the engine into production back in 1977 and 1978, but he said that his objections were ignored because the company needed the fuel-efficient diesel in order to meet fuel economy standards for its fleet.

”In test after test, we had broken crank shafts, broken blocks, leaking head gaskets and fuel pump problems,” Mr. Sand said. ”The diesel couldn’t hold up, it was a hastily converted gasoline engine with a fuel pump designed for heavy trucks.”

In 1980, Mr. Sand said he was forced to retire for causing such a fuss about the diesel. G.M., however, would not comment on Mr. Sand’s charges.

But that doesn’t quite tell the whole story either.

Although the Olds 350 block was modified for diesel use, with larger bearing areas and such, and its internal components were strengthened, the critical issue was in the cylinder head studs. In order to maximize production efficiency and have the diesel block run down the same transfer line (milling, machining, drilling), the number of cylinder head studs was not increased from the 10 per side as can be seen on this gas 350 block. Diesel engines have compression ratios up to 3x that of gas engines, thus the forces acting on the heads wanting to separate them from the block are much greater. The resultant stretched head bolts caused leaking head gaskets, which allowed coolant into the combustion chamber, causing hydrolock and other severe maladies.

The failure to increase the number of studs was a deadly mistake, and one that wouldn’t have been properly fixed without quite considerable investment in new production equipment. GM did make a number of “fixes” to mitigate this issue, with modified heads, stronger bolts and different head gasket material, all of which helped to one degree or another, but by that time, the diesel’s reputation had already caught up to it. The improved DX block version that arrived in 1982 was beefed up in a number of ways, and was essentially what it should have been in the first place.

The 4.3 L V6 that came out in 1982 did have a denser head bolt arrangement, and did not suffer the catastrophic head sealing failures of the V8.

The second deadly sin was that Olds omitted a fuel/water separator, purely for penny-pinching purposes. This was a standard item on essentially all other diesel engines. Water in diesel fuel was more common then, and removing water in diesel fuel is critical, as water corrodes the delicate high pressure diesel fuel pumps, injectors and other components of the system. Owners made the innocent mistake of adding anhydrous alcohol (dry gas) that is commonly used with gas engines to remove water from fuel, but in a diesel it dissolved fuel pump and other component seals.

Another weak spot was a stretchy timing chain; after 30-50K miles or so, the timing chain slack that would cause the injection pump to gradually fire later and later causing the pinging and detonation problems that exacerbated the “lifting” of the head and the gasket separation.

Another area that was a major concern were the glow plugs. The original pencil injectors were prone to failure and would leak sometimes contaminating the tips of the plugs. Also, when one or more glow plugs failed, owners would ruin starters and even engines with continual starting and/or lack of proper warm up. The original Stanadyne injection pumps were fitted with a plastic collar that was problem to failure. It was later retrofitted with a steel collar.

The initial version had flat tappets. These wore excessively quickly, as did the camshaft lobes. That required going to roller lifters and properly hardened cams. Crankshaft and connecting rod failures were not uncommon, quite likely as a consequence of water getting into the fuel raising combustion pressure drastically.

Compounding its woes, the diesel V8 was teamed with the new and notoriously weak THM-200 automatic transmission. The diesel 5.7 was the largest engine used with this unit, and failures were rampant. The combination of the two created huge failure rates, and even kept the diesel from being certified in California for some time. From that same NYT article:

In 1979 and early 1980, G.M. couldn’t sell its new diesels in California because test cars kept breaking down during state-run emissions tests. Thomas C. Austin, who directed the state’s Air Resources Board at the time, said that seven of G.M.’s nine test vehicles had transmission failures and all nine had engine problems. Mr. Austin, now a consultant to Consumers Against G.M., said the number of problems were ”extraordinary.”

And of course GM dealers had no experience with diesels, and were overwhelmed by angry customers. A number of customers were offered the option of swapping in a gas 350, and it was not uncommon to see an Olds with the Diesel badge on the road without the tell-tale noise and sooty exhaust.

Meanwhile, use of the Olds diesel engine soon spread across the whole GM family, starting in 1979 with Cadillac. It even became the standard engine on the new 1980 Seville, GM’s most expensive passenger car. So much for “The Standard of the World”.

Apart from all of the Olds diesel’s obvious reliability shortcomings, there’s also some questions that haven’t been asked about its performance, efficiency and actual impact to GM’s CAFE numbers.

A 1978 Olds 88 with the 5.7 diesel showed the following percentage improvement over the various gas engine versions:

3.8L V6: 20%   260 V8: 14%   350 V8: 26%   403 V8: 50%

Given that the diesel’s performance and 15 second 0-60 time was roughly comparable to the V6 and 260 V8, improvements of 20% and 14% seem pretty small, considering its higher noise, odors and soot, and most of all its extra cost of some $700-$800, which amounted to more than 10% of an 88’s purchase price.

In 1985, using the EPA’s adjusted numbers for an 88 (18 city/27 highway/21 combined), the 5.7 L diesel had only a 17% improved combined number than the Olds 307 V8 (15/22/18), which also had considerably better performance than the 5.7 L diesel.

As a point of comparison, the VW diesel Rabbit’s EPA numbers were 41% higher than the same size gas engine, and the Mercedes’ 300SD’s numbers were 47% higher than the 380SE.

Not only does it appear that the Olds diesel was not as efficient as the other diesels on the market, it also lagged in power output. The 120hp version of the 5.7 V8 made .34 hp/ci; the 1980-up 105hp version made .30 hp/ci. The 4,3 V6 made .33 hp/ci. Yet the Mercedes non-turbo 4 and 5 cylinders made .48 hp/ci, and the Peugeot .49, and the VW even made .50.

Not only was the Olds diesel underdeveloped in terms of reliability, but also in terms of performance and efficiency.

The 5.7 V8 also made its way under the hood of Chevy and GMC 1/2 ton pickups, with a 125 hp rating. The tow ratings were reduced, which strongly suggests that GM was not very confident about its abilities to handle a heavy load.

In 1979, the very short-lived LF7 260 cubic inch (4.3 L) V8 diesel joined the party. It was essentially the same as the 5.7, but with smaller bores, and made a paltry 90 hp. It was gone after its introductory year. (Note: the EPA numbers on these ads are the old unadjusted numbers, significantly higher than those used in more recent years)

Then in 1982, after the 5.7 V8 was already becoming well known for its deadly ways, Olds released the new 4.3 L V6 diesel. Essentially a 5.7 minus two cylinders, its head bolt count was increased to avoid the V8’s issues. In fact, it seems to have been a mostly satisfactory engine; it just took Olds a couple of more years to get there. The V6 was made in both RWD and transverse FWD applications, and made 85 hp, due to tightening emission standards. The 5.7 LF9 also had its power reduced from 120 to 105 hp in its later years.

Similarly to the 5.7 diesel V8, comparing the 4.3 V6 diesels EPA numbers shows only a very modest 8% improvement over the 2.5 L “Iron Duke” gas four, which had comparable output, but was of course significantly cheaper to buy.

Much like when GM wouldn’t kill the Corvair in its last years to spite its critics, Olds kept making its diesels long after the bloom had turned to a nasty stink. The LS2 version of the 4.3 V6 came out in 1985, with aluminum heads, specifically for the new FWD C platform cars (Olds 98, Buick Electra, and Cadillac DeVille and Fleetwood). How many were actually sold is another question. It was another one-year only engine, and undoubtedly finding one now, or then, would be a genuine unicorn.

Even a V5 version was contemplated, as confirmed by this prototype at the R.E. Olds Museum, and written up here.  It was presumably intended for the N-Body cars. A four cylinder is also mentioned in some articles from the time.

At the end of the 1985 MY, the glow plugs on the Olds diesels were pulled, ending not only one of the worst chapters of GM’s deadly decade of the 1980’s, but also playing a huge role in killing the diesel boom that had infected America. That had resulted in diesels showing up in all sorts of cars, including a BMW diesel engine in Lincolns. Compounding this rapid death was the fact that diesel fuel had become more expensive than gasoline, and meanwhile gas engines were improving their efficiency.

No need to beat a dead horse any longer. Let’s just say that class action lawsuits of such epic proportions forced the FTC to step in and broker an arbitration deal through the Better Business Bureau, which resulted in payments up to 80% of the cost of a replacement engine, presumably a gas one if the customer wisely demanded that. But buyers still mostly got stung, as resale values plummeted, and nobody had any interest in keeping them going, except for a few die-hard fans.

There is a lingering question that might be worth pondering: what if the Olds diesel had turned out to be a great engine? What if it had been turbocharged, and put out a healthy 200+ hp along with massive torque? The EPA numbers wouldn’t have changed, but it could have been sold as a performance engine, a viable replacement for the big blocks of yore. Would it have ushered in a golden era of big American diesels? A counterpart to the performance era of the late ’60s?

On second thought, never mind. Even my imagination has limits.

All of GM’s Deadly Sins are accessible here

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