My son brought his 1990 4.3 liter, in his Larsen, to me because it overheats. We checked for rusted out exhaust risers, checked the thermostats in 160' water, correct plug wiring, correct oil filter, cleaned carb inlet filter, timed it at 8' BTDC, total advance 28 or 29, heat gunned it, installed a known guage and sender and that verified his gauge. Pulled the outlet hose from the lower unit water pump, good flow. Removed the plug on top of the engine water pump and had great flow. The belts were glazed so we put on new ones. There is no water in the oil. Not having a closed cooling system, to easily check for a blown head gasket, I made that assumption that the gasket is blown because it overheats so quickly. I told my son "screw it, we'll pull it". I had him pull the oil filter to inspect it's pleats and look for evidence in the bottom of the filter, all good.. As he was pulling it, over some rags, I told him to loosen it and let it drain. Well he didn't listen and he spun it off and I told him not to spill any oil. Here's what's kicking my ass. There was only 1/4" of oil in the filter. This is not something that I have seen before. Any ideas would be appreciated. I'm curious what we will find.