My 97 f-150 4.6l overheats and has excessive pressure in system. I suspect a blown head gasket. I'm preparing to do a compression check. Could anyone tell me what would be a normal reading on the compression gauge?

 

You're not looking for "normal" you're looking for a "narrow range". You read all the cylinders and you don't want to have any one cylinder more than 15% below the highest. All engines wear differently so you can't predict what engine compression will be after 100K miles, but you can say they should all be pretty close to each other(withing !5%). If most are 140 and one is 75 that's a problem to look into. Do the test dry first then wet. If a cylinder fails both wet and dry do a leakdown. If all cylinders pass dry there is no need to do the wet at that point.