Oldsmobile 350 Diesel
Let's step in the Wayback Machine for a second. Pretend it's the mid '70s. Disco is popular, Saigon just fell, Nixon was pardoned, a peanut farmer from Georgia was just elected President of the United States, and gas prices are about to spike to the highest they'll get, inflation adjusted, for the next 30 years. To add insult to injury, let's briefly pretend that you're in charge of GM's product development during this time. Your customers are abandoning your large, profit-friendly cars faster than the Italians abandoned their lines during the Battle of Caporetto. As for the smaller, more fuel efficient Vega ... well, let's just say the Italian Navy was more successful against the British at night than the Vega's metallurgically suspect engine ever was against rust and engine wear. In short, you need the following
- A more fuel-efficient lineup.
- Better reliability.
- A healthy enough profit margin where dealers will actually feel compelled to take care of their customers again (i.e. not the T-Platform).
Fortunately, the solution is staring you in the face: Diesels! Diesel engines inherently provide superior fuel efficiency, less engine wear, and as an optional engine, you even get to charge extra! As if all of that wasn't enough, diesels are not subject to the sort of pollution-mitigation requirements that your gasoline engines have been laboring through. The only question is whether there's a market in the U.S. for diesels. Thankfully, the results are rather encouraging on that front--domestic sales of Mercedes-Benz's 240D and 300D are solid, and even the Peugeot 504 isn't being completely laughed out of the showroom.
So, in your capacity of head of GM product development in the late-1970s, you take the plunge. You order your minions to create a diesel engine suitable for installation in larger Chevrolets, Buicks, Oldsmobiles, and even Cadillacs. Certain in the wisdom of your decision, you step back into the Wayback Machine and fast-forward to the present day, secure in the knowledge that you've saved GM and Detroit from further erosion against the import hordes.
So ... what happened? It really was a brilliant idea, after all--better fuel efficiency, world-class reliability, and higher profit margins, all at the cost of a little acceleration that people were increasingly willing to lose. How did GM go from this brilliant concept to an engine that would eventually spawn a class-action lawsuit and inspire the drafting of Lemon Laws throughout the country? Like the Italian invasion of Greece, the devil was in the details.
Contrary to popular myth, the Oldsmobile 350 diesel was not a gasoline engine that GM hastily threw some glow plugs into. On the contrary, GM designed a block specially for the diesel 350, which was heftier and made of a different alloy than the block used in the gas-powered Rocket 350. Unfortunately, GM did cut some corners - the most egregious of which was the lack of a water separator.
To understand the importance of a water separator in a diesel engine, it's helpful to understand how a diesel engine operates. Unlike gasoline, diesel fuel doesn't ignite explosively when exposed to an electric spark. It does, however, ignite quite nicely when exposed to warm, highly compressed air. Consequently, diesel engines are built to produce incredibly high compression rates (the Oldsmobile Diesel V-8, for example, used a 22.5:1 compression ratio).
Unlike petroleum, however, water is virtually uncompressible. Consequently, when water gets into the combustion chamber of a diesel engine during the compression phase, the effective compression ratio of the cylinder increases dramatically, leading to incredible pressures in the engine. This causes increased heat, since air warms as its compressed, which, along with the higher pressures, would strain vulnerable non-metallic parts such as head gaskets and rubber seals. Of course, none of this touches on what water-based oxidation did to '70s-era metal, or that metal's ability to handle extreme heat and pressure.
This brings us to the next corner that GM cut, which led to most of the misunderstandings regarding the Diesel 350's origins. Though the Diesel 350 was given an entirely new block, GM decided it could save costs by reusing some of the tooling and parts from the similarly sized gas-powered Rocket 350. Some of the reused parts were relatively harmless bits like the valve covers, oil pan, water pump and oil pump. Fatefully, though, this list also included the Rocket 350's head bolts and head bolt pattern.
Even with a water separator, this would have been problematic--the head bolt design was meant for use in an engine generating less than half the stock compression ratio of any diesel. Without the water separator, however, the results were apocalyptic. Water would enter the cylinders via the fuel lines, which would cause higher pressures and heat to further weaken (or snap) the weak head bolts. This, in turn, would lead to the head gasket failing, which would cause a flood of incompressible water-based coolant to enter the cylinders. Once that happened, it was a battle between the compressive abilities of liquids and the ductile strength of 1970s American steel. Needless to say, the battle was over before it even started.
Sadly, there's one more exit in this cavalcade of fail. There wasn't a single Buick, Oldsmobile, or Cadillac mechanic alive that had even the faintest clue what to do with a diesel engine. It showed. When faced with failing head gaskets, the mechanics of the time did what they always did--they removed the head bolts, milled the block, then reinstalled the same head bolts. Since the head bolts were stretched from heat and pressure far beyond what they were originally meant to ever handle, it wasn't uncommon for them to fail completely shortly after re-installation. This did wonders for GM's already spotty reputation for reliability and post-sales support.
After a few years, GM was able to produce a moderately competent passenger car diesel. The Oldsmobile Diesel V6 addressed most of the problems that plagued the Diesel 350, including the spotty head bolt problem. Regrettably, the word was already out--the 350 tarnished GM's reputation in the passenger diesel market severely enough to convince GM to cease production of all domestic passenger diesels in 1985.
The first picture is from emmka on Flickr. The second picture is from the excellent collection of Cadillac ads being hosted by Flickr user "That Hartford Guy." In April 2006, Car & Driver did a "Battle of the Diesel Beaters" that featured a Diesel 350-equipped Oldsmobile 88. Proving that, if something exists, there's a fan of it, Olds-Diesel.com is an impressive if mildly misguided one-stop repository of all things Oldsmobile Diesel.
--David Colborne
mike on October 21, 2009 at 01:36 PM
Owned an 82 diesel 350. Put over 200k on it with no real issues. Changed oil every 3k with proper oil. Got 28 to 36 mpg in a delta 88. It was a slug, yes, but it road great and was very comfortable and SAFE. I liked it. Thanks for the article.
James Tucker on November 19, 2009 at 10:32 PM
I liked you artical I had a 1985 olds 98 strong engine when i got it. It had over 100k on it and when got passed it on down it was pushing 200k I would love to have another one.
Duane Hayes on December 23, 2009 at 12:15 PM
Well, there are some errors in this story. All the Olds diesels do have a fuel-water separator, it's a collector in the fuel tank that accumulates any water, then a warning light on the dash tells you to clean the water out. Now the bad part is that this requires dropping the tank, so that is inconvenient. Also the indication that there was no change to the cylinder head attachment, actually all of the Olds V-8 engines were revised with larger diameter head bolts in 1977, to accomodate the diesel engine. Hope this helps.
John on January 30, 2010 at 09:05 AM
Very correct statement on the diesel. My dad owned a 1982 pontiac bonneville diesel. Some dealership's technicians were not trained to service diesel engines. Dad's Pontiac spent more time at the dealership service bay than in his own garage. I can remember the car had "wait light" problems and would never start. The Pontiac garage went out of business and dad (still having problems with the car starting) took it to the Oldsmobile garage who inherited the Pontiac franchise in town. The mechanic there was trained on diesels and had discovered that every wire in the dash loom had been cut and spliced back together during past attempts at repairing the "wait light"problem. The owner of the dealership was involved after the diagnosis and advised dad to get rid of the car account it would need a new dash wiring loom just to start making the car reliable again - very cost prohibitive - and by now, nothing is under warranty. Dad traded his 82 bonneville for a new 86 parisienne. He lost his a$$ on the bonneville diesel trade. Dad drove that car for 5 years and traded it for a nissan maxima in 91. He has driven nissans ever since - the closest nissan dealership is 100 miles away - and the cars he has owned rarely ever need to go back there for service.
Dan on March 14, 2010 at 07:54 AM
Still drive one every day
Tars on May 21, 2010 at 12:58 PM
Thirty one years three months ago we bought a new 1979 Olds 350 diesel. It didn't get us home from the dealer with just seven miles on it. It went down hill from there. This lemon car caused us to find other GM 350 diesel victims. We organized "DieselGate" in Oregon with about seven other families, the Gillmans', the Kaufman's and a few others.
Four other GM 350 Diesel Lemon groups were formed, The Halferty's of Seattle formed Consumers Against GM and three other groups were formed in the Mid West and East Coast. These groups were responsible for the respective states lemon law(s).
The above article forgets to mention broken blocks, broken crankshafts, broken or cracked pistons, bent and broken connecting rods and many other failures common only to the 350 diesel family of diesels...
GM blamed the drivers, yet the brochure stated just use diesel fuel and drive them like any other car. I still have the 1979 Oldsmobile brochure. That brochure helped bring GM to the bargaining table.
Then GM CEO, Roger Smith was the man that brought GM out of the fine Automobile Engineering and manufacturing business into the deny, deny problems lemon automobile business. The TH200 transmission failures preceded the 350 diesel failures, yet they put the failure prone plastic governed TH200 transmission behind those 350 diesel failures. That combination insured a huge percentage of failures.
The catastrophic failures of these cars cost the consumer bankruptcy's, divorces and many other problems.
Yet GM continued to crow about how great a company it was. All the while GM continued to ignore the Japanese and German quality cars taking larger and larger shares of the American car market.. GM steadily went deeper into the toilet each year until finally all GM stockholders lost their entire investments.
Roger Smith was an overpaid money guy, he was NOT a car guy. A real "Car Guy" would have not made the piss poor decisions that Mr. Smith did. A real car guy would have not let originally lessor car companies beat them on every quality issue a car is measured by. A real car guy would not have screwed the consumer on purpose. Yet GM and its Board of Directors did just that.
We have 12 cars and motor homes in our garage and driveway, not one is a GM product.
h. ireland on May 28, 2010 at 04:38 PM
had a chevy caprice classic diesel was in the shop a few times because injection pump seal would break up and clog the return fuel line to the tank. my main problem was a wider G M ring problem on my diesel and other engines. gm switced its rec.on what oil to use in their engines. for many years it rec 10W30 multi oil. when they switched to 10W40 all hell broke loose! the problem was sticking oil ring to pistons. how about 1 qt of oil per 400 miles! remedy take out glow plugs put in a GM solvent the dealer left in over night . did not work. GM ended up going back to 10W30 oil. took a beting on resale. gm had engineering problems galore.
Andreas Winter on October 05, 2010 at 02:07 AM
I own one of these Oldsmobile Diesels and it is quite reliable if it is not exposed to water in fuel. The fuel efficiency is remarkable for a car of this age. Actually the water in the diesel fuel was not a problem in Germany. Our fuel was quite clean. Although I bought my car in the U.S. and it seems to be one of the few survivors.
Brett Cannon on February 24, 2011 at 04:11 PM
My first car was a 1980 Pontiac Bonneville 2-door 350 diesel. I loved that car, but yet it was another GM development that had not been tested throughly. Great car, engine not so great. This was of of the best articles on this infamous engine that i have ever read.