Diesel engines have a deserved reputation as reliable workhorses, but that doesn’t mean all diesels can be relied on to perform well and last.
While diesel engines have their benefits — fuel economy, towing capacity, torque, and a reputation for ruggedness and longevity — they aren’t without their faults. The worst diesel engines can be so unreliable, underpowered, and problematic that they can have their owners wishing they had stuck with gas. Older diesel power plants, in particular, have a reputation for producing plenty of smoke and noise, along with a litany of engine troubles. Smoky diesel exhausts have been rectified in newer models via emissions abatement technology — but many owners are finding that the newer technology comes with its own shortcomings.
Some owners of newer pickups claim the emissions tech is causing problems up to and including catastrophic engine failure, with forums overflowing with tales of owners who « delete » their engine to overcome EPA constraints and « bulletproof » it to eliminate factory flaws. « Deleting », in this context, means removing the emission controls, while « bulletproofing » means rectifying an engine’s known faults.
However, extensive bulletproofing can cost more than the engine itself, while a diesel engine delete can be a bad idea for a number of reasons. Apart from landing the owner in legal trouble, a badly executed delete can also cause engine problems. Of course, none of these problems would arise if defective diesel engines were not put into trucks in the first place. By way of warning, these are some of the worst diesel dogs, according to their regretful owners.GM LF9 5.7L ‘Oldsmobile 350’
The GM 5.7L LF9 diesel is a legendary engine for all the wrong reasons. Some owners firmly believe the Olds 350 single-handedly destroyed the U.S. market for diesel engines — and yes, it was that bad. One of the worst American diesel engines ever built, the LF9 started life in 1977, sharing many similarities with GM’s V8 gas engines, including 10 cylinder head bolts per side.
Posting on El Camino Central, retired diesel tech trainer Sleepy78 lists « weaknesses across the board », including head bolts insufficient in both number and strength, no means of separating water from fuel, poor oil and fuel filtering, carbon build-up causing rocker and pivot wear, plugged radiators, overheating, crankcase blow-by, oil leaks, and starter motor issues. Sleepy said they picked up Olds 350s virtually free in the 1990s and early 2000s « as no one wanted to be associated with these popcorn machines. » Over on The Truck Stop forum, another owner recounts buying a 1981 C10 pickup with 80,000 miles and already on the second engine, which died at 125,000 — not before guzzling a quart of oil every 50 miles.
On the Diesel subreddit, BadBadBenBernanke describes the 350 as « a forgettable engine that powered some forgettable cars », while Proof-Surprise-964 says it had « the acceleration of a sail boat. » SimilarTranslator264 says his family owned two 350s, with only one making it to 100,000 miles. « Not only were they loud and didn’t like cold weather but they also didn’t make much power and didn’t last long either.
