Do a crankcase flush by adding 2-3 quarts of Diesel fuel or kerosene to a fresh change of oil. I'd suggest using straight 30 weight detergent oil, not some kind of fancy multi-weight stuff. Run the engine at a fast idle, maybe 1000-1500 RPM for about 30 minutes.
DO NOT DRIVE THE TRUCK OR PUT ANY LOAD ON THE ENGINE DURING THE FLUSH!
Drain the oil/Diesel mix immediately after shutting the engine down, while it's still hot. Any sludge or other crud that's built up over the years will drain out with the oil. By overfilling the crankcase enough to make the crankshaft and connecting rods dip down into the liquid, it splashes the thinned-out oil around like the agitator in a washing machine, doing a better job of cleaning than you could possibly do with a brush and solvent. In the process, it should dislodge any carbon under the piston rings that might keep them from doing a good job of oil control.
Even if this procedure doesn't help with the oil consumption, you'll have to do a lot less cleanup of the crankcase when you do an overhaul.
Jerry
