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. 

1983-87 International/Ford 6.9L IDI

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.

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.
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.

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 forward a little with the 130 hp 6.2L diesel but you can see the common theme. A high buy-in for the privilege of owning a gutless wonder.

The Ford version of the 6.9L differed in several respects from the International. The secondary fuel filter was mounted on the engine behind the alternator. The primary filter/water separator was mounted on the firewall next to the power brake booster. Also, the Ford had a vacuum pump mounted under the alternator (not shown here) for the vacuum boosted brakes. Ford used a lower profile air filter to fit under the lower pickup hood. Typically, the ‘83 model year Fords were rated at 161 horsepower at 3300 rpm and 307 lbs-ft at 2000 rpm. With the compression boost to 21.5:1, that rating went up to 170 horses and 315 lbs-ft at 1800 rpm. The compression boost to 21.5:1 may have come before the ‘83 Ford model year was over, but we haven’t confirmed that yet. Engine with serial numbers from 59209 and up had the higher ratio and some of those are said to have appeared in 1983 production. We’d like to verify that.

Few knew that International Harvester was working on a new diesel that answered the needs of truck owners from Class 2 through Class 6 (6,000 to 26,000 pound GVW). IH was in the midst of corporate upheavals and red ink but their medium-duty line was a high spot worthy of an investment. A new low-cost diesel was one of those investments. Like most medium-duty lines, the lower GVW end of the IH line was populated with gas V8s, many of those legacy engines from the ‘50s. Beyond the fuel economy angle, they were almost beyond hope of meeting future emissions regulations and being built on tooling that was worn out.

Target Specifications

The engineering target was for a moderately priced V8 diesel in the 400-450 cubic inch range, making 165 net horsepower at 3200-3500 rpm. After engineering and marketing outlined the basics, execs approved the project in 1977. The serious design work started in March of 1978 with a goal of starting production in March of 1983. The development had a good shortcut, the recently developed medium-duty MV404 and MV446 gas V8s intended to eventually replace the old V-345, V-392 and even older V-478. The new diesel borrowed some of the basic MV architecture and allowed the new diesel to be built on the same new tooling. The proposed 420 cubic inch diesel used the same stroke as the MV-446 but had a smaller 4.00 bore (0.125 inches smaller).

When the suits come to pose, you know it’s a done deal. Here, from left to right, are three VPs; G.D. Aravosis from Marketing, W.A. Wallace from Engineering and V.P Spedale General Manager besides one of the prototype engines. The image accompanied an October 31,1980 press release from the IH Components Group, which incorporated the Indy Engine Plant. The Indy plant had long been IH’s gas engine factory and diesels were built up at Melrose Park, Illinois. As gas engine production slowed, more space was available and diesel production was ramped up at Indy until all the gassers were gone. Indy built all the light and medium-duty diesels for corporate use and those sold to Ford into the 6.4L era. The Indy plant closed in 2009.

In that era, Indirect Injection (IDI) was the easy answer to meeting upcoming diesel emissions requirements and it also delivered better fuel economy than the DI engines of the day. Probably the main reason was low cost, the IDI requiring a much less expensive injection system. In those days, the Ricardo Comet Mark V swirl combustion chamber was the rage. Sir Harry Ricardo had developed the basic design in 1931 and though advances in fuel injection technology would soon tilt the advantage to direct injection, the Ricardo Comet V was a viable answer for the 1980s and was used in many engines of the day.

First Engines

The first prototype engine was completed in August of 1979 and 160 more followed. Early tests highlighted the need for better injectors. The first ones tried were an outward-opening poppet injector that did not deliver anything near the target power level and failed quickly. A temporary breakthrough was achieved by installing a set of two-orifice nozzles from another IH application, getting them through the initial tests and into field testing. It took a while to figure out the right combination of injector, injector targeting, combustion chamber location and compression ratio. The orifice nozzles proved non-optimal from an emissions standpoint, and they were sooting up, so new inward opening pintle injectors were designed and they integrated well with the Stanadyne DB2 rotary pump.

The 6.9L owes it’s basic architecture to the 1975 MV-404 (2 and 4-barrel) and MV-446 (4-barrel) gas engines. No, the 6.9L was not a “gas engine with diesel heads” but the engines shared many features, the same basic dimensions and some parts. New tooling had been built for the MV engines and IH wanted to use it for the 6.9L.  The 6.9L and MV-446 crankshafts were nearly identical, though inside sources tell us the heat treating was different. The MV engines had two-bolt mains and the diesel had four-bolt. Both the gas and diesels used the same gear drives for the cam and oil pump. The MV heads were tied down with four bolts per cylinder and the 6.9L with five. The rocker gear is similar as were the valve covers. The MV series engines had a relatively short life, just seven years (1975-81) to the tune of 120661 404 and 446 engines. This is also a dressed-up show engine. Normally, they were painted red.

A total of 21,000 dyno test hours were accumulated at 3300 rpm, full load, peak power and some 52,000 test hours total. Starting in September of 1980, prototype engines were installed into trucks and field tested, with over 813,000 test miles accumulated. Once all the bugs were discovered and dealt with, they built 10 preproduction engines on the new line and some were tested a further 1,000 hours at full power on the dyno and then out in the field. Actual production started in August of 1982, beating the original timeline estimate by seven months.

Enter Ford

Once the concept was proven and testing well underway, IH began actively shopping the engine around. International wasn’t interested in supplying other medium-duty manufacturers but light-duty was another matter since they had discontinued their own light line by then. Ford Motor Company was on the hook almost from the start. Being only slightly larger and heavier than their existing 460 bigblock V8, it was a sure fit in Ford light trucks. Ford opted to offer it only in light trucks with an 8,500 pound GVW, or more, meaning F250HD and F350 models. That included the Ford E250 and E350 vans but not Ford’s medium-duties. It began a business relationship that lasted 30 years, though it ended badly.

The ‘84-87 Ford sea level and high altitude power graphs show a flat torque curve from idle to about 1800 rpm. The 1400-1800 rpm range is the sweet spot for these engines.

Ford started installing 6.9L engines in August of 1982, first at the Twin Cities Assembly Plant and at all the relevant truck plants shortly thereafter. Until about March of 1983, you could only get it with a manual trans until the tooling was ready to mount the C-6 behind it. Ford advertised 161 horsepower at 3300 rpm and 307 lbs-ft at 2000 with a 19.7:1 compression ratio. These specs come from Ford Data Books, brochures and Ford Facts Books dated August and September of 1982. The early magazine tests listed these specs as well. International documents from the same era show the engine with a 20.7:1 compression ratio and it’s very likely the 19.7:1 ratio listed is either a preliminary number that was changed or incorrect. As it was, the 20.7:1 ratio delivered cold starting issues and it was increased to 21.5:1 for 1984 with piston and cylinder head changes.

Impact on History

In the medium-duty market, the 6.9L added an entry-level diesel into International’s 1600, 1700 and 1800 lines, both busses and trucks, with GVWs up to 26,000 pounds. That was good for International’s bottom line but it didn’t rock the medium-duty world and other manufacturers followed suit with similar engines. It sounded the death knell International’s medium-duty gas engines, including the relatively new MV series. Production of gassers at IH (later Navistar) dwindled into the hundreds of engines by the mid ‘80s and had ended completely by 1988.

The lower end is very stout for the era. Shown is a 1986 engine during an overhaul. You can see the four-bolt mains and gear drives.

The 6.9L was replaced by the 7.3L IDI in 1988, which acquired turbocharging in it’s final year of production, 1994. A total of 436,868 6.9L engine were built from August of 1982 to August of 1987. The HEUI diesel emerged in ‘94, called the T444E by International, and Powerstroke by Ford. By then, International Harvester had been broken up. The Motor Truck Division, including the engine manufacturing component, became Navistar International.

The weakest link of the 6.9L are the head gaskets and head bolts. Modern head gaskets with an ARP head stud kit cures this weakness.

The 6.9L had more significance in the light-duty market and talking about it forces us to risk inciting GM versus Ford rivalry. GM beat Ford to the punch with the intro of the 6.2L diesel for 1982. It was a far better engine than the 5.7L it replaced but was still low on power. The 1982 6.2L GM diesel emerged with 130 horses and 240 lbs-ft. (135 hp in HD emissions) and stayed at those ratings until later in the ‘80s. The 6.9L emerged for ‘83 at 161 horsepower and 307 lbs-ft but was up to 170 horses and 315 lbs-ft by 1984. The 6.2L was available in all GM trucks into the C/K 30 realm and did pretty well in the half-ton lines. It was less stellar mounted in hard-working 3/4 and 1-tons where low power delivered mediocre loaded performance and some significant degradation in reliability.


Two 1986 Ford F-250HDs. Left: What was done. Right: What Gale Banks did and Ford/Navistar should have done to rock the world. Banks came out with a non-wastegated turbocharger kit for the 6.9L in 1984. It made about 10 psi boost, and Banks advertised 255 horsepower and 550 lbs-ft. The first generation kit on the right was installed by the original owner when the truck had 7,000 miles. It’s still there and can still put 200 horses to the rear wheels.

The buy-in was still pretty high for both engines (vs a big block which was around a $500 for both FOrd and GM) so recovering those costs from fuel and maintenance savings could take a while. The 1983 GM 6.2L diesel option was $2375 ($1334 engine plus $1041 for the required diesel equipment package). For ‘83, the complete Ford 6.9L option at  $2225 for the 4×4 and $2543 for the 4×2. Considering the power difference, which was the better deal? Not to disparage the 6.2L, but in looking back, and using boxing metaphors, you could say the 6.2L was a lightweight or welterweight in it’s output and construction. The 6.9L was a solid middleweight or maybe a light heavyweight. The GM 6.2L was a good and economical choice in a half-ton but if you towed or hauled, the Ford 6.9L was the better choice. Today, most would sneer at a 170 hp NA diesel with 315 lbs-ft, but in the early ‘80s those numbers gave you some braggin’ rights.


You May Also Like

The Best Diesel Engines: Top 10 Of All-Time

From the farm to the highway, construction equipment to gen-sets, and emergency vehicles to the trucks we drive every day, diesels have built—and continue to build—America. Even beyond our…

BMW 3.0L I-6 M57: Small Displacement Diesel

It’s an engine that is tough as nails, extremely efficient on fuel, and highly affordable at the present time, yet some of you never knew it existed—until now. It’s the 3.0L M57 inline-six…

DT466 Diesel Engine: The Navistar International Legend

Legend! That’s a powerful word that might be used a little too often these days. When it comes to the DT466 diesel, though, it fits. Especially, when you consider it came from users in the…

Head Gasket Failure: 6.7L Cummins

No matter the power plant, the natural design of the internal combustion engine—where the cylinder head(s) bolts to the block—lends itself to eventual head gasket failure. While not…