Hello, This is one area that I know a little something about since I have followed these diesels for years. In the early 70's, GM was looking at worsening fuel prices and their existing production lines for large automobiles and declining sales. The Oldsmobile division spent time and money looking at ways to improve fuel economy in their larger automobiles. One promising avenue was to design and build a diesel engine with the BPOC (Buick, Pontiac, Oldsmobile, Cadillac) transmission bolt pattern that would bolt up in existing production lines.
AFAIK, in 1974 Olds was testing a diesel engine that was built from an 5.7L Rocket spark-ignited gasoline engine using a belt-driven IP. These tests were a complete failure and Olds realized that they couldn't use anything more then just external accessories from existing engines. Everything else for the new diesel engines had to be custom designed including the block. The myth that the later 5.7L and 4.3L diesels are converted gas motors is completely false. The blocks have a higher nickel content and 4 bolt mains and a different crank size then the small block Olds gas motors. The engines used two different types of injectors, pencil and poppet types that while custom spec'd for this application were derived from agricultural use injectors. These are supposedly far more efficient designs then the more typical Bosch style injectors that are in widespread use. In 1982, EPA testing showed that the 1982 Oldsmobile 98 full-size car was getting 32mpg on almost a 5000# car. These engines were available across the entire GM product line from 1979-85 and still to this day rank 4th on eBay as the most numerous diesel passenger vehicles. Why do this engines have a terrible reputation and why did GM drop the whole project and buy third-party diesel designs? There are many answers and the truth is probably some of all of them. The biggest issue that the engines had were in head gasket failures since they seemed to fail much more rapidly then other gas engines of the same time frame. Another answer is that these engines were designed for fuel economy and not horsepower and owners tried to expect too much from the engines. A third answer is that in the early 80's diesel fuel quality was said to be at a all time low and non diesel savvy owners would buy diesel fuel in places where the fuel had been contaminated via water or algae. The head bolts were installed by some early robotic equipment using stretch to torque fasteners. These fasteners were not adequate to the job and most believe were primarily selected due to compatibility with the new robotic equipment. The head bolts were not adequate for the task and routinely failed causing head gasket leaks in as few as 30-50K miles. In some cases, 100K were reached, but many didn't reach that point without failure. GM didn't take the time to properly research the problem and for the dealers, it was faster to replace the entire motor then troubleshoot the dead one. Dealers hated to deal with the vehicles due to the constant service issues and customers hated the vehicles since the problems didn't stay fixed. One issue with the head bolts were they were designed to be one use only applications. Either through neglect of training or not caring enough, many GM technicians would reuse the fasteners that "looked" okay and only replaced the "failed" bolts. Of course, it wasn't long before the head gasket failed again and the engine was blamed to be a poor design. Replacing the head bolts with solid ARP aftermarket fasteners has resurrected many Olds diesels. The website http://www.olds-diesel.com is a good source of information concerning these engines and the automobiles that they were installed in. Many fixes and improvements over factory original have been made and many users drive "transplanted" engines in vehicles. One of my personal favorites is the Diesel Fiero that is running the 4.3L V6 diesel. Todd Smith <[EMAIL PROTECTED]>
