40‑Year‑Old Diesel Engine Still Going Strong – Reliability, Mileage & Price

Bottom Line Up Front

This 40‑year‑old diesel engine is still in production because it’s unbelievably reliable, cheap to run, and surprisingly affordable.

40‑Year‑Old Diesel Engine Still Going Strong – Reliability, Mileage & Price

Image: 40‑Year‑Old Diesel Engine Still Going Strong – Reliability, Mileage & Price – Performance Comparison and Specifications

Design & Looks

When you first see the block, nothing screams “modern” – it’s a plain iron cylinder head, a sturdy cast‑iron block, and a single turbo that looks like it belongs in a 1990s pickup. That simplicity is the secret sauce. Fewer electronics mean fewer things that can break, and the engine can be lifted out of a truck with just a few bolts.

I remember my uncle’s old 1998 Dodge Ram – the same engine was humming under the hood for over 300,000 miles. He never needed a computer scanner; a quick visual check and a wrench did the trick.

Performance & Mileage

Despite its age, the engine still delivers respectable torque – around 300 lb‑ft at low RPMs – making it perfect for hauling and off‑road work. Fuel economy sits near 30 MPG on the highway, which is better than many newer diesels that sacrifice efficiency for power.

Torque: 300 lb‑ft @ 1500 rpm
Power: 150 hp @ 3500 rpm
Fuel Use: ~30 MPG highway, 22 MPG city

The engine’s low‑end grunt means you rarely have to downshift, which saves fuel and reduces wear on the clutch.

Price & Rivals

Newly built units sell for roughly $30,000, a fraction of what a comparable modern diesel costs. Competitors like the newer 6.7L Power Stroke or Cummins 6.7L start north of $45,000 and come with complex emissions kits that can be costly to service.

Because the older engine lacks advanced emissions hardware, owners avoid expensive OBD‑II repairs and can often keep the vehicle on the road for years with just routine oil changes.