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When Diesel Was Dreadful: the General Motors 6.2

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author photo by Aaron Gold February 2017

In my previous installment of When Diesel Was Dreadful, I discussed Oldsmobile's hapless V8 and V6 diesels, the engines that singlehandedly ruined the compression-ignition engine's reputation in the United States. Today, let's turn our attention to these engines' undeservedly maligned corporate cousin, the 6.2-liter diesel V8.

Contrary to what many believe, the 6.2 is not related to the Olds 5.7. GM wanted a diesel alternative for their light trucks, and having learned their lesson -- somewhat -- from the Olds debacle, they decided to pair with an experienced diesel builder. As luck would have it, they just happened to own one: the Detroit Diesel division. (One wonders why no one thought of this when the Oldsmobile engines were being developed.)

There was only one wee little problem: Detroit Diesel wasn't in the 4-cycle business. Way back in 1938, when it was still known as the GM Diesel Division, Detroit Diesel developed the 2-cycle 71-series engine, named for its per-cylinder displacement. The 71 (and later 53 and 92 derivatives) went on to rule the bus business, and were also popular for trucks, boats and stationary generators. If you rode any sort of city or over-the-road bus between the late 1940s and the early 1990s, chances are it was powered by a Detroit 2-stroke diesel. Known as "Screamin' Jimmys" (here's why) these engines were always happiest running wide open.

I've read that the 6.2 was Detroit's first 4-cycle engine, though I haven't been able to substantiate this from enough reliable sources to bless it as true. Nevertheless, Detroit Diesel took a pretty conservative line: This was an iron-block, iron-head, 379 cubic-inch engine using a 2-valve pushrod valvetrain. It was designed to bolt up to the engine mounts and transmissions used in GM's light trucks. The engine was not turbocharged, and it used the same Standadyne DB-2 mechanical injection pump as the Oldsmobile V8 (which may account for the same crinkly-crunchy soundtrack and the rumors that the engines are related).

The engine bowed in 1982, and was offered on Chevrolet and GMC pickups and Suburbans. Power output was, ahem, modest -- 130 horsepower (135 in some applications) and 240 lb-ft of torque, roughly equivalent to the output of Volkswagen's 2.0 liter 4-cylinder turbodiesels. Fuel economy was the real goal here, and 6.2-liter trucks could achieve 15 to 20 miles per gallon.

Incidentally, I have some familiarity with this engine: I own one, along with the 1983 GMC Suburban that surrounds it. Every drive in the 'Burb (when the starter isn't acting up, that is) is a reminder of why diesels were so reviled: It takes a long glow-plug cycle to warm them up, and it takes two batteries to develop the cranking speed needed to fire. Acceleration is excruciatingly slow, and I'm lucky to top steep hills at 45 mph. That said, once it gets going it just keeps on going, and it doesn't matter whether the Suburban is empty or full: It'll crest the hill at that same 45 mph. My engine has covered 196,000 miles and runs pretty well, or at least as well as these engines ever run. I'm told it will continue to run forever, provided I replace the harmonic balancer, which has a nasty habit of coming apart and destroying the entire engine. I see around 15-16 mpg in mixed driving -- and with a 40-gallon fuel tank, I only need to hit the fuel station a few times a year.

In 1992, GM and Detroit produced a new version of the engine enlarged to 6.5 liters, though the 6.2 would continue in production through the 1993 model year. The 6.5 was offered both with and without turbochargers -- and in order to bring the engine into compliance with new on-board diagnostic (OBD) standards, 1994 saw the exchange of the old DB-2 pump for an electronically-regulated DB-4. These engines powered GMC light trucks as well as the military HMMWV and its civilian counterpart, the Hummer H1.

One might expect the 6.2 to have faded into history, but it hasn't: It remains an inordinately popular engine among enthusiasts, and survivalists in particular. The 6.2 is an entirely mechanical engine, with no electronics whatsoever. If the block is warm enough and the cranking speed high enough, the engine will fire and run, even after the black helicopters knock out civilian electronics with their electromagnetic-pulse machines. Gale Banks still catalogs the Sidewinder turbo system for the 6.2. Why? Because it still sells.

I almost feel bad writing about the 6.2 under the "dreadful" headline; it may be a humble engine, but it does the job it was asked to do. (That said, I've also owned a 2-cycle Detroit -- a 6V71 installed in a GM city bus, if you must know -- and it started easier and ran smoother than my 6.2.) But it wasn't until Chrysler upped their game with the Cummins 6BT -- and GM matched it with the Duramax 6.6 -- that people finally began to take GM diesels seriously ... so maybe "dreadful" isn't the worst way to describe this engine after all.

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This image is a stock photo and is not an exact representation of any vehicle offered for sale. Advertised vehicles of this model may have styling, trim levels, colors and optional equipment that differ from the stock photo.
When Diesel Was Dreadful: the General Motors 6.2 - Autotrader