GM singlehandedly destroyed any possibility of diesel engines being accepted in the U.S. for the last three decades!!! The thing that has always frustrated me is WHY those engines were so prone to failure (head-gasket failure was the #1 problem and often happened before 10k miles)! It was so typical of the old GM…
The vast majority of GM passenger car diesels were based on the Oldsmobile 350 (5.7L) V8. Many people erroneously claim that the Diesel 350 was just a hastily converted version of the gasoline 350, hence the problems. But that’s actually far from the truth!
The GM 350 Diesel V8 may have shared some dimensions with the Olds 350 Gas V8, but the Diesel 350 was not based on any existing GM engine, gasoline or otherwise. It was engineered from the ground up to be an oil-burner!
Diesel engines must be able to handle MUCH greater compression rates and stresses than any gas engine. Gasoline engines achieve combustion by squirting a specific mixture of fuel and air into the compression chamber where it is ignited by a spark (which is why gas engines need spark plugs). Diesel engines achieve combustion by compressing the fuel/air mixture in the compression chamber until the pressure generates enough heat to ignite the fuel. Diesel engines don’t have spark plugs.
The reason diesel engines have traditionally been very durable and long-lived is because they’re built to deal with much higher pressure required for them to operate. The engine block is usually thicker and made from stronger materials than gas engines. They also tend to have more head bolts and a stronger head design/construction. Diesels also make most of their power at much lower engine speeds (max torque at 1800rpm and max horsepower at 3600rpm for the 350 Diesel). They rev slower and ‘redline’ at much lower engine speeds than gas engines also. A Gas 350 V8 might redline at 5500rpm while the 350 Diesel had a 4000rpm redline.
The bore and stroke as well as many other dimensions were shared with the Olds 350 V8, but that was done so the same tooling could be used to manufacture both the Gas and Diesel 350. GM rushed the Diesel into production in an effort to be the domestic “leader” offering an economical diesel on most of its mid- and full-sized cars.
There were TWO major problems that weren’t addressed or went unnoticed prior to production that caused the VAST majority of these engines to have major problems and many eventually suffered ‘catastrophic’ or total failure.
While the Diesel 350’s engine block and head was beefed up to handle the much higher compression ratio, they used the same head bolts and studs that were used on the Gas 350! There should have been a greater number of head bolts used and the studs and bolts should have been made from heavier, beefier materials. The inevitable result was that the head would separate from the block slightly under pressure and blow the head gasket! The dealer would remove the head and machine it to make it fit snugly once again, then install a new head gasket and RE-USE the same head bolts which were made even weaker from the failure and caused the new head gasket to blow even faster than the first one!
The other fatal flaw has to do with the nature and quality of diesel fuel at the time. Diesel fuel absorbs water much from the atmosphere much easier than gasoline. Diesel engines require a precise fuel/air mixture for proper combustion and the fuel delivery system is very complex. Many parts of this complex system are made of steel or other metals which corrode easily. Water in the fuel creates rust throughout the fuel delivery system and caused multiple problems. Water in the combustion chamber could also cause rust in the cylinders, which could lead to any number of problems including bent/broken connecting rods (which is roughly equivalent to tossing a grenade inside the engine)! All diesel engines need a water separator (often integrated or adjacent to the fuel filter) to remove any water from the fuel before it wreaks havoc on the engine! It’s an essential part of diesel technology both then and now….but somehow GM overlooked or forgot to include this low-cost device!?!?
In addition to the atrocious reliability problems, the performance of the 350 Diesel V8 was considered inadequate by most drivers. A 1981 Cadillac Seville with the 350 Diesel V8 took an agonizing 21.0 seconds to accelerate from 0-60mph! To put that in perspective, a 1981 Chevy Citation with a 2.5L 4-cylinder and 3-speed automatic could do 0-60 in 14.2 seconds, which was almost 7 seconds faster than the Cadillac but still considered just adequate!
The 350 Diesel was rushed to market for the 1978 model year and they kept the god-awful thing in production thru 1985! A 4.3L V6 Diesel was added to some mid-size models starting in 1982, with versions for both FWD and RWD platforms. It only made 85hp (20hp less than the 350) but it was relatively trouble-free and performed as well or better than the much large V8! I knew a man who worked at the GM Plant here in Atlanta in the early 80s and he ordered his wife an ’85 Cutlass Ciera Brougham 4-door with the 4.3L V6 Diesel. It performed trouble-free for more than 200k miles!
High times!
