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International Harvester’s Mid-1970s Truck Lineup
By 1975, International Harvester had firmly established itself as a major player in the medium and heavy-duty truck market. The Loadstar and Fleetstar series dominated municipal fleets, farms, and small construction outfits. These trucks were known for their rugged frames, simple mechanical systems, and a wide range of engine options. International offered both gasoline and diesel engines, with displacements ranging from 304 to 549 cubic inches. The company’s in-house engine development led to a diverse lineup, including the MV, RD, and V-series blocks.
Terminology Note
A common point of confusion arises when older International trucks are retrofitted or misidentified. In one case, a 1975 single axle truck was mistakenly believed to be a 1965 model and possibly equipped with a 7.3L diesel. However, the 7.3L engine—known as the T444E in International applications and used by Ford as the Power Stroke—was not introduced until 1988. Its predecessor, the 6.9L diesel, debuted in 1983. These engines were based loosely on the MV gasoline block architecture but are not interchangeable without significant modification.
Given the truck’s actual build year of 1975 and its gasoline configuration, the most likely candidates are:
How to Confirm the Engine Model
To identify the engine definitively:
In Pennsylvania, a contractor restored a 1969 Loadstar 1600 with a 345 CID engine. He discovered that the same block family included the 304 and 392, allowing him to swap parts across models. In Oregon, a mechanic rebuilt an MV404 and found that the water pump matched the 6.9L diesel’s—highlighting the shared lineage between gasoline and diesel blocks.
Oil Recommendations and Maintenance Tips
For older gasoline engines like the MV404 or RD406:
The engine in a 1975 International single axle truck is almost certainly a gasoline unit from the MV or RD series, not a 7.3L diesel. By checking casting marks, line setting sheets, and block features, owners can identify the engine accurately and maintain it with confidence. These trucks represent a bygone era of mechanical simplicity and remain serviceable with basic tools and a bit of detective work.
By 1975, International Harvester had firmly established itself as a major player in the medium and heavy-duty truck market. The Loadstar and Fleetstar series dominated municipal fleets, farms, and small construction outfits. These trucks were known for their rugged frames, simple mechanical systems, and a wide range of engine options. International offered both gasoline and diesel engines, with displacements ranging from 304 to 549 cubic inches. The company’s in-house engine development led to a diverse lineup, including the MV, RD, and V-series blocks.
Terminology Note
- CID (Cubic Inch Displacement): A measure of engine size based on cylinder volume.
- MV Series: Medium-duty gasoline engines introduced in the mid-1970s, including the MV404 and MV446.
- RD Series: Red Diamond engines used in heavier trucks, such as the RD372, RD406, and RD450.
- Line Setting Sheet: A factory build sheet listing all installed components, often found behind the cab seat.
A common point of confusion arises when older International trucks are retrofitted or misidentified. In one case, a 1975 single axle truck was mistakenly believed to be a 1965 model and possibly equipped with a 7.3L diesel. However, the 7.3L engine—known as the T444E in International applications and used by Ford as the Power Stroke—was not introduced until 1988. Its predecessor, the 6.9L diesel, debuted in 1983. These engines were based loosely on the MV gasoline block architecture but are not interchangeable without significant modification.
Given the truck’s actual build year of 1975 and its gasoline configuration, the most likely candidates are:
- MV404 (6.6L)
- MV446 (7.3L)
- RD406 or RD450 (6.7L or 7.4L)
- V-series engines like the 345 or 392 CID, commonly found in Loadstar 1600 and 1700 models
How to Confirm the Engine Model
To identify the engine definitively:
- Check the block casting: Look for stamped numbers near the distributor or valve cover.
- Inspect for a diamond logo: RD engines often have a cast-in diamond on the block’s right side.
- Locate the line setting sheet: This may be glued behind the cab seat or stored in the glove box.
- Contact an International/Navistar dealer: Provide the truck’s serial number for historical build data.
In Pennsylvania, a contractor restored a 1969 Loadstar 1600 with a 345 CID engine. He discovered that the same block family included the 304 and 392, allowing him to swap parts across models. In Oregon, a mechanic rebuilt an MV404 and found that the water pump matched the 6.9L diesel’s—highlighting the shared lineage between gasoline and diesel blocks.
Oil Recommendations and Maintenance Tips
For older gasoline engines like the MV404 or RD406:
- Use 15W-40 in warm climates or 10W-30 in cooler regions.
- Avoid synthetic oils unless the engine has been rebuilt with modern seals.
- Change oil every 3,000 miles or 100 hours of operation.
- Inspect valve cover gaskets and rear main seals for leaks—common in older blocks.
The engine in a 1975 International single axle truck is almost certainly a gasoline unit from the MV or RD series, not a 7.3L diesel. By checking casting marks, line setting sheets, and block features, owners can identify the engine accurately and maintain it with confidence. These trucks represent a bygone era of mechanical simplicity and remain serviceable with basic tools and a bit of detective work.
