The 4.8L was rated at a peak 175 horsepower in automatic transmission applications and 142 horsepower in applications with a manual transmission. The engine is notable for its low end performance; although the automatic transmission equipped engine produces peak torque at 2,000 RPM, the engine's nearly 5 inch stroke and undersquare bore-to-stroke ratio provide considerable torque at low engine speeds. Transmission options were a Isuzu MXA-5C 5 speed manual, Isuzu MZZ 6 speed manual, or an Aisin-Warner 450-43LE 4 speed automatic. While both the 6 speed manual and 4 speed automatic transmissions feature overdrive, the 5 speed manual transmission's final gear was direct drive (1:1).
4.8L Isuzu 4HE1 Specs
| Engine | Isuzu 4.8L 4HE1-TC | |
| Manufacturer | Isuzu Motors Ltd. | |
| Applications | 1999 - 2004 Isuzu NPR 1999 - 2004 Isuzu NQR 1999 - 2004 GMC W3500, W4500, W5500 1998 - 2001 Chevrolet W4/W5 Tiltmaster |
|
| Type | 4 Stroke diesel | |
| Configuration | Inline 4 cylinder (I-4/L-4) | |
| Displacement | 4.75 liters, 289.96 CID (nominal 4.8 liter/290 CID displacement) | |
| Firing Order | 1 - 3 - 4 - 2 | |
| Engine Block | Cast iron | |
| Cylinder Head | Cast iron | |
| Cylinder Liner Type | Dry | |
| Compression Ratio | 17.3 : 1 | |
| Cylinder Bore | 4.330 inches (110 mm) | |
| Cylinder Stroke | 4.921 inches (125 mm) | |
| Valvetrain | Single gear driven overhead camshaft (OHC), 2 valves per cylinder | |
| Valve Clearance | Intake | 0.4 mm |
| Exhaust | 0.4 mm | |
| Injection | Direct injection | |
| Aspiration | Turbocharged & intercooled | |
| Engine Oil Capacity | 14.5 U.S. quarts (13 liters) | |
| Engine Oil Viscosity | Varies by ambient operating temperature; see chart below | |
| Horsepower* | Manual transmission | 142 hp @ 2,800 rpm |
| Automatic transmission | 175 hp @ 2,700 rpm | |
| Torque* | Manual transmission | 275 lb-ft @ 1,300 rpm |
| Automatic transmission | 347 lb-ft @ 2,000 rpm | |
| Max Engine Speed | 2800 - 2900 rpm (max rpm @ full load) | |
*NPR, NPQ, and GM W4500/W5500 gross horsepower ratings
Transmission Options & Ratios (NPQ/NPR Models)
| 1st | 2nd | 3rd | 4th | 5th | 6th | R | Remarks | |
| Isuzu MXA-5C | 6.020 | 3.626 | 2.017 | 1.367 | 1.00 | --- | 6.030 | 5 speed manual, synchronized, direct drive |
| Isuzu MZZ-6F | 6.369 | 3.767 | 1.966 | 1.355 | 1.00 | 0.782 | 6.369 | 6 speed manual, synchronized, overdrive |
| Aisin Warner 450-43LE | 3.018 | 1.548 | 1.000 | 0.703 | --- | --- | 2.678 | 4 speed automatic, overdrive |
Isuzu 4.8L 4HE1 Maintenance Schedule
| Service Procedure | Service Interval | Notes |
| Replace engine air filter | Every 26,000 miles/12 months | Check condition of air filter at oil change intervals & replace as necessary, or every 26,000 mi/12 mo |
| Replace engine oil & oil filter | Every 6,500 miles/12 months | Engine oil level should be checked between oil change intervals |
| Replace fuel filter | Every 13,000 miles/12 months | Replace fuel filter & drain fuel water separator |
| Replace engine drive belt | 104,000 miles | Check condition of drive belt at oil change intervals & replace as necessary; replace regardless at ~100,000 miles |
| Drain/replace engine coolant | Every 26,000 miles/24 months | Drain/refill cooling system and inspect condition of coolant hoses; replace as necessary |
| Adjust valve lash | Every 52,000 miles | Set intake & exhaust valve lash to 0.016 in (0.4 mm) |
| Replace automatic transmission filter & fluid | Every 26,000 miles/12 months | Replace internal and auxiliary transmission filters as applicable |
| Replace manual transmission oil | Every 19,500 miles/12 months | Drain/refill transmission |
| Replace rear differential oil | Every 26,000 miles/24 months | Drain/refill differential |
Isuzu 4.8L 4HE1 Oil Viscosity Chart
| Oil Viscosity | Ambient Temperature Range |
| SAE 10W-30 | -20° F to 90° F |
| SAE 10W-40 | -20° F + |
| SAE 15W-40 | 0° F + |
| SAE 15W-50 | 0° F + |
| SAE 20W-40 | 0° F + |
| SAE 20W-50 | 0° F + |
| SAE 10W | -20° F to 32° F |
| SAE 20W | 0° F to 60° F |
| SAE 30W | 32° F to 90° F |
| SAE 40W | 75° F + |
| SAE 50W | 75° F + |