Curbside Classic: 1978 Oldsmobile Delta 88 Diesel – In Defense of the Olds 350 Diesel V8


(first posted 4/4/2013. It’s an example of CC offering alternate points of view, in this case to our Olds 5.7 L V8 Diesel Deadly Sin Post)

My Grand Dad always had a beater, for everyday driving, and a good car, which he bought new and brought out only on special occasions. Once, he said he’d buy a new car when he retired and give his current garage queen, a 1966 Chrysler sedan, to my Dad. In 1977, Grand Dad did retire, and Dad held him to his word.  To replace the Chrysler, he headed down to Carter Chevrolet-Olds and placed an order for what is oft regarded today as one of General Motors’ biggest blunders: a 1978 Oldsmobile Delta 88 with the then-new 350 cid LF9 V8 diesel engine.


The Delta 88 4-door sedan was the most popular 1978 Olds to be ordered with the LF9 diesel. Much like the base-model 1966 Chrysler, the 1978 Oldsmobile Delta 88 was advertised as more car for not much more money than “lesser” automobiles. Undoubtedly this appealed to Grand Dad’s innate frugality, as it still allowed him to have an upscale, but not ostentatious, full-size automobile.

Aside from the special engine, Grand Dad had ordered his Olds equipped in pretty much the same way as his Chrysler. Both were finished in metallic maroon, his favorite color. Inside, both had an AM radio but no other optional power or comfort accessories. The Olds came with a rear window defroster, which I believe was part of the upgrade to the larger alternator that was mandatory with the diesel.


At the time, rising gas prices were certainly of concern, as were the Rube Goldberg-style emissions controls that strangled the gasoline engines of the day.  On paper, the diesel engine looked to be a godsend:  Advertised fuel economy for the LF9 was head-and-shoulders above the other engine choices, even with a three-speed, non-lockup automatic transmission.  Today, the performance figures of the LF9 (rated at 120 hp) would be considered laughable, but at the time they bested the contemporary European diesels on the market.

(Image source: Popular Mechanics, Sept. 1978, via Google Books)

Early buyers were initially very pleased with their purchase.  A survey of 1,000 Olds diesel buyers, published by Popular Mechanics in September 1978, reported that 97.4% said they would buy another Olds diesel!  Also, owners were actually getting fuel mileage that came close to the EPA numbers.  Then came the inevitable breakdowns.  The engine quickly garnered a bad reputation as a lemon, and eventually became the poster child for why America ultimately rejected diesel passenger vehicles.  So what went wrong?


It’s a common misconception that the Oldsmobile LF9 diesel was simply a 350 small block hastily jerry-rigged to run on diesel fuel. This misconception came about because the locations of cylinder-head bolts and some other critical dimensions were identical to the gas-fed small block so that both blocks could be machined on the same equipment during manufacture.

(Image source:

The LF9 engine block was a unique casting with extra reinforcement; the entire reciprocating assembly also was unique, with all its components heavy-duty. The larger, 3-inch-diameter main bearing journals it used in place of the normal 2.5″ journals were the same as in a big block; however, its commonalities with the garden-variety small block made it possible to bolt gasoline-engine heads onto the LF9 block, and (along with other modifications) convert it into a gas engine.

While some industrious engine builders have overcome the technical hurdles to accomplish this, the rework costs make it impractical for all but maximum-performance applications. A converted LF9 can be generously over-bored and built for higher power than a regular small block without grenading in racing applications.

Diesels are very sensitive to water contamination in the fuel system. Diesel fuel contaminated with water results in much higher-than-normal combustion pressure–high enough to blow head gaskets and snap head bolts. It is true that the LF9 head bolts were under-designed, especially on those built prior to MY 1981. The problem was exacerbated by improperly trained dealership mechanics who had to service this engine. When changing a blown head gasket, they typically would just replace any snapped head bolts, just as they would on a gas-powered GM V8. However, the diesel used “torque-to-yield” head bolts that required the entire set to be replaced when changing a head gasket. Otherwise, more head bolts were bound to fail, and the vehicle would soon be back in the shop in need of another head gasket.


Unfortunately, as a cost-cutting measure GM did not outfit their diesel cars with a proper water-separating fuel filter. A “water in fuel” (WIF) sensor was installed in the fuel tank, as well as a warning light on the dashboard. In the Delta 88 the WIF lamp would have been located in the panel above the HVAC controls. The WIF warning lamp was GM’s work-around for the lack of a proper filter. Owners ignored this warning light at their (and their vehicles’) peril. Compounding the problem, some well-meaning owners simply added “dry gas” (alcohol) to the fuel tank when the WIF light came on instead of having the fuel tank drained. Alcohol is incompatible with diesel fuel-injection systems and ruins the seals in the injection pump.


In my memory, the only times Grand Dad actually drove his Olds were on the way to my brother’s birthday party every August, to his annual summer visit to his brother in Maine, and (begrudgingly) during a short stint one winter, when his beater needed repairs. I remember him keeping the block heater plugged in to ensure there wouldn’t be any starting problems in the cold weather. It was the only time that block heater was used.

I also recall Grand Dad briefly putting the Olds up for sale. He had somehow convinced himself that he wanted a Thunderbird Turbo Coupe. It wasn’t for sale very long, either because the only interested parties were tire-kickers that wanted to lowball him on price, or because after my Dad informed him that the turbo-bird drank premium gas, he didn’t want one after all.


After Grand Dad passed away, in 1989, my Dad inherited the Olds. It became a regular summer driver in our household, but remained stored safely away from winter weather and the ensuing road salt. I’ve personally logged a fair bit of time in the driver’s seat. In 1999, the year I graduated from school and started my full-time career, I borrowed the Olds for most of the driving season. Defying the odds (considering its poor reputation and the over 130,000 miles on the odometer), the original power plant still resides underhood in relatively original condition (including head gaskets!)  That this car is still with us today, and hasn’t exhibited most of the usual maladies these engines were known for, can be credited to a combination of good maintenance practices and good fortune.


Early production cars didn’t even get the water-in-fuel sensor, so a recall was issued to retrofit it. Some time after receiving his new car, Grand Dad was notified of the recall notice. When he went to the dealer to have the WIF sensor recall applied, he was told that it was no longer being performed, and instead they would install a fuel filter. In reality, they were probably being lazy; the recall procedure involved draining and removing the fuel tank to install the sensor and disassembling a fair amount of the dashboard to install the WIF warning lamp.

What the shop actually installed–a big blue canister visible in the engine compartment–is the kind of  large diesel-fuel filter  typically found on commercial trucks. There is a petcock at the bottom for periodically draining off any water it has collected. I attribute the uncharacteristic longevity of our Olds to this filter as much as anything else.


Another common problem with these engines involved their propensity to eat camshafts and crankshafts. In both cases, that could be avoided by using the correct diesel-rated crankcase oil and changing it promptly at the prescribed 3,000 mile intervals (or preferably sooner). The first-gen used a flat tappet camshaft, but the valve spring pressures were considerably higher than would be typical for stock gasoline engines. Additionally, the crankshaft bearing material was designed for use with diesel-rated oil only. If you slacked off on the oil change interval, and trusted your car to whatever oil the local monkey-lube installed, valve train and/or bearing failure was inevitable. Ultimately, GM made the engine more tolerant of typical owners’ maintenance habits: The second-gen LF9 diesels received roller cams and revised bearings, which extended their service interval to 5,000 miles and permitted the use of non-diesel-rated oil.


This particular car has enjoyed every-2,000-miles oil changes with diesel-rated 30W oil since it was new. The rockers wore out and needed replacement once, but the rest of the valve train is original. Naturally, there have been other repairs over the years. For instance, one of the cylinder heads developed an external crack in the water jacket and my dad, who figured he had nothing to lose, simply welded the crack shut, with the head still on the car. It worked!

Another time, one of the plastic T-fittings on the fuel return lines cracked. Diesel fuel spraying on the exhaust manifold resulted in billowing white smoke from under the hood; fortunately, it didn’t ignite. The Stanadyne fuel injection pump has required two overhauls, and the injectors one. Presently, the car has a small fuel-system leak somewhere, probably just a cracked rubber fuel line, that causes the pump to lose prime after sitting. It requires lots of cranking to re-prime the system before the engine clatters to life.

In typical fashion, GM rushed the LF9 engine to market with a combination of underdevelopment, beancounterism, and lack of dealership-mechanic training. After weathering a barrage of bad press from reviewers and purchasers during the engine’s first few years, they cancelled production despite finally having gotten most of the bugs worked out. Of course, by the mid-80s, gas prices had fallen, there were government threats to more closely regulate diesel passenger-car emissions and the LF9 had developed a bad and seemingly unshakable reputation. It had basically become unsalable.


If only GM had installed a proper fuel filter, made some of the second-gen improvements up front, and taken the time to properly train their dealership mechanics in servicing the engine. No, they’re not for everybody–the LF9 was still an old-school diesel with no turbo to give it more power, nor electronic fuel injection to quiet it down–both of which are ubiquitous on moderns diesels–but still, I think diesels could have had a future in full-size American sedans.  There was already an established niche market for them among European-car buyers, who were turned off only by the lack of dealer support for their imports.


Based partly on our own favorable experience with Grand Dad’s Olds, my family got hooked on the economy and low maintenance costs of diesel power.  We’ve since owned several VW diesels, GM 6.2-liter diesels, a Cummins-powered Dodge and a Chevy Duramax.  If diesel power had continued to be an option in domestic full-size sedans, this list probably would be even longer.

(Most pictures for this article not taken by my Dad were sourced from

Related reading:
Automotive History: 1978 Oldsmobile 5.7L Diesel V8 – GM’s Deadly Sin #34 – Premature Injeculation