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.