Differences in 6.5L Engines?

[duallycc]

Hey All;

The Olds 455 in my 73 GMC motorhome is giving out, and I'm going to replace it with a TD 6.5L (it's been done before). I'll be looking for a candidate engine, and I'm wondering if there are any differences between the 6.5L in a half ton or 3/4 ton or a 1-ton truck? I had heard that there was on the 6.2L, but haven't heard anything on the 6.5L. Any info would be appreciated. Thanks.

GaryB in Wa.

[DmaxMaverick]

Welcome aboard!

There is a difference, in most cases. Generally, the 1/2 ton and some 3/4 tons have an "S" code (8th VIN digit) L56 engine (RPO code, sticker in glove compartment), while the 1 ton, and some 3/4 tons have an "F" code L65 engine.

S = EGR, light duty smog.
F = No EGR, HD smog, more stock power.
(the 6.2L was C or J, respectively)

Any S code engine can easily be converted to a virtual F. Only minor hardware and software (if it's a 94 or later, EFI) is required. If planning on a mechanical fuel system, no electronic concerns. The F can be used without a vacuum pump, while the pump is needed for EGR (both) and wastegate control (EFI). If your motorhome doesn't require a vacuum source for other systems (HVAC, brake assist, etc.), this may be desirable. None of the vacuum systems on any of the Diesel engines are suitable for vacuum brake assist, especially on a heavy vehicle, like a motorhome (conversion to hydroboost is highly recommended, if it applies).