A Mercedes-Beater That Went Down in Flames

It’s not going over the top to say very few engines had more impact on the American light diesel market than the Oldsmobile 350 V8. Here’s how it all went down.

The 1970s is when carefree American motoring went fully into the toilet. Thanks to the Arab oil embargos, fuel economy became the motoring public’s fixation. At the same time, emissions regulations had brought the mighty American V8 to its knees and choked-down cars and trucks couldn’t chirp a tire while sucking way more fuel that was suddenly four times as expensive. A 55-mph national speed limit was the disgusting condiment on a fecal matter sandwich.

The auto industry struggled to meet the challenges and addressed the issues in many ways, including by looking at diesel power. Hey what’s not to like about 25-35 percent better economy on fuel that’s 10-15 percent cheaper? (Then, not now.) Unfortunately, the American auto industry didn’t have suitable automotive diesels in-house. Asian and European automotive diesels were highly developed but generally small four-cylinders for compact cars. Those played well over there but everyone knew America wasn’t quite ready to abandon full-size cars and trucks.

A dolled-up display “D” engine from the 1978 model year. Olds initially rated the new V8 diesel at 120 hp at 3,600 and 220 lb-ft at 1,600. The Chevy pickup was 125 hp and 225 lb-ft. Allegedly, the new diesels were real-world-tested for a year before the rollout and were installed in GM fleet cars, taxis and police cars. General Motors, specifically the Oldsmobile Division of General Motors, thought they could combine diesel economy with the traditional American car. All they needed was a diesel engine capable of powering the existing platforms that didn’t cost too much. Mercedes-Benz had fielded the most highly regarded diesel cars up to that point and Oldsmobile set the mark at beating Mercedes at its own game. In theory, they had a pretty good shot at it.

In an SAE white paper from February of 1978, Olds engineers said their diesel quest began in 1973. They started big by installing GMC’s 478ci V6 Toro-Flow diesel into a full-sized car. Since Opel in Germany was an arm of GM, they tested an Opel Rekord four-cylinder diesel in a mid-sized Olds. They also tried a Nissan SD33 six-cylinder diesel in a full-sized car.

The Toro-Flow was physically too big and emissions-dirty. The 2.1L Opel was too small for a mid-size and the 100hp, 165 lb-ft, 3.3L Nissan six was too small for a full-sized car. They didn’t have many other choices without downsizing their car line, so they decided to develop a new engine in-house. The stout, reliable, fits-in-existing-platforms Olds 350 cubic-inch V8 gasoline engine came to mind as an architectural pattern.

Suppress that sneer! To that point in history, basing a diesel on gas engine architecture had occurred many times, most often successfully, and it allowed a manufacturer to use similar tooling for both engines. Conversions generally demanded an IDI combustion chamber, since they deliver a slower and lower pressure rise on the firing event and the engine structure can be lighter. IDI science was well explored at that point but Olds soon learned none of the previously developed IDI combustion chambers were suitable. They tested 300 combustion chamber combinations over a three-month period before settling on a design.

When they installed test engines into cars, a pleasant surprise emerged. The goal had been to equal the performance of the Olds 260ci economy V8 (110 hp/205 lb-ft) in a full-size Delta 88 chassis. The 350 diesel ended up being a little faster—0-60 in 17.5 versus 20.8 for the 260 in the same 4,500-pound ’75 Cutlass test car. Diesel fuel economy was way better— 26.5 mpg versus 19.5 at a steady 55 mph and 21.4 mpg versus 16.7 on the EPA composite test. The 1978 production diesels were EPA rated at 21/30/24 in the full-size platforms. The same car with a 350 V8 gasser delivered 15/22/17. The diesel option cost $740 in a 98 Olds where the base engine was the 350 gas V8.

Meet the Oldsmobile 350 LF9 Diesel

The original 350 diesel “D” block shared the same 4.047×3.385 bore and stroke as the V8 gasser and the same general dimensions, but was only 75 pounds heavier. The complete diesel car was only 135 pounds heavier than the gasser, half of that being the second battery. The internal bulkheads and main bearing support webs of the D block were beefed up and the deck thickness increased. The nodular iron crankshaft was similar to the gas V8’s, but main bearing diameters were enlarged from 2.5 to 3 inches, the cheek structures were increased in size, and the pin lightening holes were eliminated. The connecting rods were significantly enlarged and the piston pin diameter went from 0.978 to 1.11 inches. Needless to say, the pistons were completely different, with steel inserts behind the top compression ring. The compression ratio was a whopping 22.5:1. 

The heads were completely new but the valves were the same size as the gas 350’s. The heads were held down by then-new TTY (Torque To Yield) style bolts with four bolts per cylinder. The cam profile was altered to suit the diesel and the camshaft material was improved from ordinary cast iron to hardened Conkerall iron. The lifters were a tungsten-titanium alloy steel. The cam and injection pump was driven by a double roller chain.

The engine was fueled by a Roosa-Master DB-2 rotary pump from Stanadyne fed by a mechanical lift pump. The injectors also came from Stanadyne and were a new design they called Pencil Nozzles. They had two 0.017-inch orifices (0.014-inch in California) and popped at 1,800 psi.

The Oldsmobile diesel was introduced on September 13, 1977, in the Delta 88 and Ninety-Eight platforms, as well as the Custom Cruiser station wagon and the Chevy C10 pickup. For mid-year 1978, the mid-sized Cadillac Seville, which Cadillac liked to think of as its Mercedes-Beater, also got the diesel option.

All Hell Breaks Loose

The launch started well and the press favorably compared the Oldsmobile diesels to Mercedes. Surveys done of new customers early in ’78 were reported to be 97 percent positive. Olds was selling a lot of diesels, about 60,000 that first year, plus the Chevy trucks and Sevilles (a total of about 129,000 engines). The American public appeared to be accepting the diesel and its quirky ways. Then the fecal matter hit the fan. 

The 1981 “DX” engine was the one GM should have made first. The upgrades included better head gaskets and stronger head bolts that threaded more deeply into the block. The main cap bolts were also better and more deeply threaded into the block. A new roller hydraulic lifter was developed with a new cam profile to suit. A stronger oil pump driveshaft was added. A water-in-fuel sensor was included on cars starting late in 1980 and a retrofit kit offered for earlier cars. In ’85 a fuel filter with a water separator was added. Along the way GM replaced the pencil injectors with a poppet style and if you compare this picture to the ’78 engine nearby you can see the difference in the injectors and lines. These later engines were downrated on power to 105 hp, which was probably a survival element as well.

The head gaskets failed. Four TTY head bolts were not always enough to hold the heads down. Sometimes they sheared but most times the gasket failed first. Either way, when the car ended up at the dealer, some mechanics didn’t replace the TTY bolts, or they torqued new ones incorrectly, and if the bolts didn’t break the first time, they did the second. Sometimes the head gasket failure started slowly, contaminating the oil and killing the bearings and/or the camshaft before the head gasket blew.

Injection pump and injector failures occurred. Often this was due to water in the fuel (common in that era). To save money, GM had opted NOT to include a water separator, a water-in-fuel sensor or a tank drain. In some cases, an injection pump failure occurred because people added an alcohol-based “drygas” product.

The 350 diesel-powered Chevy and GMC light trucks were serious fuel misers and if all you expected was six-cylinder performance, you were happy. Anecdotally, it appears the trucks were less trouble than the cars but the reason is not clear.

Camshafts were going flat, despite the improved materials. If it didn’t come from an internal coolant leak it was often related to the lubricants used. GM prescribed a strict 3,000-mile oil change interval to protect against soot buildup, which was made worse by the EGR system, and there wasn’t much fudge factor in the oil change interval. The lubricant specified was a diesel-certified API CE/CD oil, uncommon at gas stations and car repair shops of the day. Non-diesel-rated oil was being used both for changes and top-off, often with some “expert” telling the owner: “It’ll be fine!”

Going to the high end, the Olds Toronado, which had just been downsized and shared a platform with the Cadillac El Dorado, was optionally powered by the 350 diesel and offered top-dog luxury with a 21 mpg EPA combined average and a 0-60 time of 16.8 seconds. Sure, the previous year big Toronado with a 403ci V8 did it in 12.5 seconds, but it delivered only 14 mpg combined.

Lower ends were failing. If it didn’t come due to contaminated, incorrect or sooted oil, the “chicken” in that scenario was broken or pulled main bearing cap bolts. Turns out the threads weren’t tapped deeply enough and the bolts were too short. The oil pump driveshaft had a tendency to shear off, but from what little detail is available, it looks like this was often a side effect of oil sludging due to coolant or soot contamination.

The Cutlass Cruiser Brougham was a great “Mercedes-Beating” idea. This decked-out car could expect high teens/low 20s fuel economy in town and scratch at 30 mpg on the highway. Acceleration was decent and on par with the base gas engines. The EPA combined rating was 25 mpg with the 350 diesel, while the base 3.8L V6 was only 18 mpg. The Olds diesels ended up being faster than the Mercedes diesels of the era. The production Oldsmobiles delivered 0-60 in about 16.5 seconds, give or take, with a top speed of 90 mph. The four-cylinder Mercedes 240D automatic did 0-60 in 23.4 seconds, the five-cylinder 300D automatic did 21.7 seconds and the five-cylinder 300D Turbo automatic made 18.1 seconds. Mercedes had at least one edge: Their engines were as reliable as gravity.

Despite it being a stout double roller design, timing chains stretched. This didn’t cause a sudden catastrophic failure but retarded the cam and pump timing, leading to poor performance, higher EGTs, increased noise, excess smoke, hard starting and more strain on the weak head gaskets. This problem was easily fixable by resetting the timing and, if caught early, was no harm in and of itself. 

Finally, it came to light that dealer personnel were in an informational vacuum when it came to dealing with the many warranty problems rolling in. A good number of the follow-up failures were due to inadequate repairs the first time around. The non-dealer repair shops were even deeper in the dark, and more inclined to “wing it.” That was a two-edged sword that sometimes yielded good but non-GM-authorized fixes, and other times hackmeister repairs that added to the car owner’s trouble.

The Blowback on GM

Class action lawsuits ensued and we can thank the Olds 350 for bringing us the Lemon Law, which forces manufacturers to buy back defective cars. The J.D. Power Company sprang into prominence when it published a big survey on the 350 diesel problems. GM spent millions upon millions in paying off claims and has yet to fully get past the reputational hits. Surviving executives and engineers from that time period are probably still experiencing PTSD events.

The Hit on Owners

Based on period sources, an estimated 25 percent of everyone who bought an Olds diesel in the ’78-79 model years had major trouble. They faced a lot of obstacles at first with the inability of GM to fix the cars properly. There are tales of people spending exorbitant amounts of money to get the cars fixed after the warranty ran out. The resale value of Olds diesels went straight into the sewer. Even people who had no trouble with their Olds diesels felt the pain. Fearing a problem, they preemptively attempted to trade them in, and found dealers offering dismal trade-in value or even refusing to take them in trade. 

Shared Blame

GM was the chicken that laid the bad eggs. Barring a better initial product, a faster response to the problems could have saved many headaches. Some of the heat must also go to service people, some of them representatives of General Motors, who dropped the ball and added to the problem. Finally, shame on the owners who couldn’t be bothered to read or follow the recommendations in their owner’s manuals. 

The Legacy

There was a time when the words “Oldsmobile” and “diesel” could not be used together without the speaker hawking a big loogie onto the ground. Forty years later, the legacy of that event is still very evident. There isn’t much doubt the fallout soured the majority of the American public on diesel. It’s also true that the problems were magnified in the retelling and it became fashionable to bash GM.

There were a lot of Olds diesels that had no trouble at all, or the problems that occurred were dealt with satisfactorily. The better dealers and techs stayed up on the problem and once GM realized they had a major PR issue, they encouraged dealers to take proactive steps. Competent techs, responsible dealers and diligent owners avoided most of the trouble. When working well, the cars were nice drivers and the fuel economy was just what gas-crunch-shocked owners needed. If GM had spent a little more time on the details, they could have had their Mercedes-Beater and been credited as the foundation of the American diesel car world, not the destroyer of it. 


Leave a Reply

Your email address will not be published. Required fields are marked *

You May Also Like

HSP Diesel Duramax S300 Turbo System

Making 500hp in a 2001 to 2010 GM Duramax is easy, right? While easy may not be the right word, the Duramax is a very capable engine; with the right combination of parts (good tuning,…

1942 Cummins HBIS Engine

By the late 1930s, the diesel engine was rising to meet the needs of a market growing ever more friendly. The support infrastructure was improving and diesels had made leaps and bounds in…


Why You Want It: When you need a winch to work, no matter what, you want a Walrus. Made by ComeUp USA, these winches are highly regarded, very popular and widely used around the world.…