Re: 1989 5.7L w/69 hours siezed from sitting
For gosh sakes don't use the starter or bigger breaker bar. Loosening an engine requires patience and a delicate touch -- unless of course you want to breake the starter houseing, the mounting surface on the engine block and/or the ring lands on the pistons. Forcing the engine loose can cause more damage than you already have. As was mentioned, pull the plugs, dump in any rust breaker like PB Blaster, Tri-Flo tec., and definitely not SeaFoam. Let it sit for several days. Using a standard breaker bar, gently try moving the bar in both directions. GENTLY. If no movement is detected. Walk away for a few more day adding more PB Blaster if needed. Try again. At some point you will be able to get a very slight amount of movement. DO NOT force the engine past the limits. Just keep inserting PB Blaster and gently rocking the crank back and forth. When it is fully free, add regular engine oil and spin the engine a few times with the bar. THEN switch to the starter. At this point a compression check can be done but because of all the oil in the cylinders the resulting readings may be artificially high but it will at least indicate presence or absence of a catostrophic problem. Insert the plugs, fuel it up and see if it runs. Yes -- it will smoke until the oil is burned off. And be sure to have water to the engine while you do this test run. Some engines can seize to the point where they cannot be loosened so keep that in mind. Those have typically injested water and have not been turned since.
