Public and governmental outcry after the oil shortages of the early ‘70s forced U.S. auto, light truck and commercial truck makers towards economical diesel power. Inroads had already been made getting more diesels into the Class 3 through 6 commercial medium trucks, and the higher GVWS had good coverage, but Class 3 and 4 were still often powered by little more than beefed-up passenger car engines. To that time, there wasn’t much incentive to develop diesels for Class 3 and 4 because the thrifty buyers of those trucks, mostly in-city short hoppers, were not keen on the usual 20% price premium. Rising fuel costs changed those attitudes but lower cost diesels were needed to push the idea across the finish line.
Fuel economy concerns soon became a factor with Class 1 and 2 light trucks (half to one-ton) as well. Diesels were part of the answer there too but there were few suitable diesels available and the industry addressed it in a short-sighted, haphazard way. Examples of that in the mid-late ‘70s included the 80 hp 3.3L Nissan in International’s Scout SUV and pickup lines, the 100 hp 4.3L Mitsubishi inline in Dodge D/W150-250 trucks and the infamous 120 hp 5.7L Olds diesel in half-ton GM trucks. In the early ‘80s, GM stepped
This is the 1982 International version of the 6.9L, dolled up with chrome and snazzy blue paint. Initially, International had two ratings, 155 horsepower at 3000 rpm and 305 lbs-ft at 1600 rpm or 165 horsepower at 3300 rpm and 310 lbs-ft at 1800, both of those with the early 20.7:1 compression ratio. For ‘84, the common IH ratings were 155 horsepower at 3000 (305 lbs-ft @ 1800) and 165 horses at 3000 with 321 lbs-ft at 1600 rpm. Ratings up to 170 horsepower at 3300 in trucks were allowed. Advertised was a 180 horsepower rating for marine engines. The 6.9L had oil cooled pistons, four-bolt mains, roller tappets, oil cooler, gear driven cam and injection pump, inboard combustion chambers (injectors at top of engine), exhaust valve inserts and positive valve cooling. The crankshaft was a forged unit and the block was cast of nodular iron. The heads were tied down with five bolts for each cylinder.
From 1980, here is one of the prototype 6.9L diesels. Compare it to the1983 image a little farther on. Looking to the right of the picture, you see a strange square corner. This was the Phase 1 oil cooler, which was a complex plate-type design. For production, a more compact tube-bundle style was used. Note also the differences in the upper timing gear cover. At 780 pounds dry and without ancillaries, it was a relatively light diesel. DEDICATED TO THE LATE TERRY HANKINS, IH/NAVISTAR ENGINEER