This factory service and repair manual for the 1988 GMC W6500 Forward covers two diesel engines of different sizes and different induction: a naturally aspirated 6.5L inline-six of 396 cubic inches and a turbocharged 5.8L inline-six of 353 cubic inches. Both are fitted to the low tilt straight truck under the W6R042 code. A shop that runs one of each will find their specifications, torque values and diagnostic routines set out separately rather than merged into a single set of figures.
Engines covered
- 6.5L inline-six (396 cu in) — naturally aspirated, diesel
- 5.8L inline-six (353 cu in) — turbocharged, diesel
Body styles covered
- Straight truck, low tilt
Trims covered
- W6R042
Known issues on the 1988 W6500 Forward. There are no recalls on the federal record for the 1988 W6500 Forward and no owner complaints registered with NHTSA against it. What the manual is left to cover is the mechanical range itself, the naturally aspirated 396 cubic inch six and the turbocharged 353, with the procedures, specifications, torque values, wiring diagrams and diagnostics needed to keep either version working.
