Yes it is the start cap that I am blowing, I replaced the cap and the first time it started, the cap blew oil everywhere. I looked and there is a centrifugal switch on the rotor. I also looked at the compressor, and there is no valve between the compressor head and the tank. There is just a line going to the pressure switch. I checked the safety and it wasn't stuck, and it has never popped open so I don't thing I have an over-pressure situation. My first thought was that maybe my shop is just too hot, but when I put that new cap on, it blew the first time it started, and the shop was pretty cool it rained last night so it was fairly cool.
I rotated the compressor by hand, and it feels like it turns pretty easily, I can hear the compression cycle and that seems fine.

Is there a positive and a negative side of the capacitor? It wasn't marked on either connector. Could I have connected it backwards? I know the small electrolytic caps will blow when connected backwards but those are marked.

Thanks for setting me straight on the single phase (split phase) motors, come to think of it I had read about that, but must have skipped over it.

Jim