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The Oldsmobile Diesel V8: The US diesel engine killer

Charl Bosch By:
Wednesday, November 28th, 2012 08:14 am GMT +2

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By Charl Bosch

Back in 1973, General Motors was facing a massive problem. The international oil crisis had resulted in the slumping of sales in the full size automobile segment which was where GM made their primary cash.

In an attempt to curve the crisis but also to satisfy the government’s Corporate Average Fuel Economy (CAFE) regulations introduced in 1975, GM had  to downsize their luxo barges but in doing so, they also had to lower the output of their V8 engines to balance power with efficiency.

For 1978, new regulations stipulated that passenger cars had to average at least 18 MPG (13 l / 100 km) which meant that GM’s last option to remain profitable was to go the diesel route. Not wanting to spend more money on developing a completely new engine, GM turned to their Oldsmobile division with their well-established Rocket 350 V8 engine which was regarded as one of the most reliable engines at the time.

The diesel, officially called the Oldsmobile 350 diesel V8, shared many of its components -remember this – with the Rocket V8 engine and was claimed to average up to 30 MPG (7.8 l / 100 km) depending on the car fitted to. As if on cue, the Olds diesel as it effectively became known, arrived for the 1978 model year and was immediately popular. During 1980, Oldsmobile made 910 306 vehicles of which 126 885 were diesels.

GM quickly took notice of the Olds’ popularity and on the back of the 1979 energy crisis, began to offer the Olds diesel as an option on certain Pontiac, Chevrolet and Cadillac models. This happened at a time when GM was consolidating engine offerings in its various products meaning that it was not unusual to have your Oldsmobile fitted with a Chevrolet engine.

What happened shortly after the Olds diesel’s introduction however, ruined the reputation of diesel engines in North America as well as that of GM and Oldsmobile which was the best-selling nameplate in North America at that stage and the only marque to have made one million cars in a single year.

After much research, the reasons for the Olds diesel becoming the automotive equivalent of Chernobyl are as follows: Like the Rocket V8, the diesel used torque to yield bolts which were not strong enough to cope with the higher pressures that diesel engines are subjected to; hence the bolts provided inadequate clamping forces.

Ultimately, these blots would crack over time which lead to head gasket failure and with coolant leaking into the cylinders, the phenomenon of hydraulic lock would set in, resulting in bent connecting rods and crankshafts.

However, there were two big reasons why the Olds diesel flopped. Firstly, it lacked a water separator in the fuel system which, given the quality of diesel at the time and the fact that the engine’s internals were mostly made from steel, caused it to rust eventually leading to the failing of injectors, fuel lines and fuel pumps.

Secondly, owners and dealership personal were totally unfamiliar with how a diesel engine operated. Many owners would, in attempt to get rid of water build up, poor hydrous alcohol (dry gas) into the fuel tank. The technique was known to work with the Rocket V8 but with the diesel, the water absorbed the alcohol laden dry gas causing massive damage to the fuel system’s injector flex rings resulting in the engine’s timing going out.

Once in the workshop, service personal simply had no training done on how to repair diesel engines and would simply mend the engine in the exact same way as the Rocket V8 because the parts fitted and the engine under the hood resembled the Rocket engine. The chances then of the already damaged head bolts being used again was almost guaranteed effectively resulting in multiple gasket failure.

What’s more, the diesel engine was an expensive option over the petrol unit. If you wanted the diesel in your Oldsmobile Delta 88 for example, you had to pay an extra $850 which was a 15% increase over the Rocket V8. The diesel was said to have been very unrefined, made a loud clatter and emitted a terrible smell together with huge dollops of smoke.

During the period 1978 to around 1985, power outputs for GM’s V8 engines, being Cadillac, Chevrolet or Oldsmobile engines, ranged from as low as 82 kW to as high as 127 kW. The Olds diesel displaced 5,737 cc, was normally aspirated and came in three outputs during its life.

Between 1978 and 1980 the Olds diesel, marketed with a “D” on its block produced 93 kW and 305 N.m of torque for commercial vehicles and 89 kW with 300 N.m of torque in passenger cars. From 1980 until 1985 and now sporting a stronger “DX” marked block, the diesel made 78 kW and 278 N.m of torque. As popularity began to dip and problems continued to escalate, GM attempted to revive interest in the Olds diesel by introducing a smaller and much improved 4.3 litre V6 in 1982 with just 47 kW and 224 N.m. However the damage had already been done and diesel engine production ended after 1985.

In theory, the Olds diesel could and should have been a success but it was ultimately led down by shoddy engineering and a total lack of knowledge. In the end, a class action law suit resulted in GM having to pay customers back 80% of the cost of a new engine. Ironically, when properly looked after, the diesel was known to be reliable and ran for miles without problems. In my view, the diesel fiasco caused more harm to GM than the Chevrolet Corvair saga.

Recently, GM announced that it plans to offer the same diesel engine used in the facelift Cruze to power the eight generation Malibu mid-size saloon that recently went on sale in the States and in Australia as a Holden.  If this would to happen, I hope that Americans will embrace the Malibu diesel and truly see the benefits of diesel passenger cars.

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PLEASE NOTE: The opinion expressed in this article is the author's own and publication does not mean it is endorsed by the CAR magazine editorial staff or RamsayMedia, publishers of CAR magazine.

    excellent article

    • Charl Bosch

      Thank you very much neoriginal. Comment much appreciated

  • Ian

    I had a 1979 Caprice Classic Station Wagon with the V8 Diesel We drove to the french Riviera and managed to get home to Birmingham.
    It caused a great deal of amusement to my American friends who knew the reputation of that terrible power plant!

  • Question Authority

    I had a 79 Olds 98 with that damned diesel motor. What a Jimmy Carter POS
    that junker was! It was a 350 alright but had a whomping big ol’ starter that
    would have fit a Mack truck. It would burn brushes out as it tried to turn the
    diesel over. The car looked and sounded like a steam shovel when it started;
    lots of noise and clouds of black smoke, which was a constant source of
    laughs from neighborhood boys. It was like a Model T Ford in that each time
    you went somewhere you had to top up the radiator and engine oil because
    it burned and leaked both prodigiously. I prayed for the day that damned
    motor finally died, and it did, after 8 months of HELL. I bought a new Olds
    98 with a GAS engine and had no trouble at all with it.

    • nigel

      Oldsmobile disappeared during 2004, but the current GM Diesel 6.2L / 6.5L and Duramax 6600 engines are as good as any other current diesel engines.