A simple indication of "blow-by" is oil leaking out at the PCV Valve, or, even worse, is oil leaking out at the gaskets (valve cover, fuel pump if older motor, LOL, Rear Main, Head, etc.)
Blow By is the compression in the cylinder leaking back past weak rings, causing positive pressure in the crankcase, ultimately causing oil to push out of any available openings, and, when worse, it makes it's own openings to come out.
The real method to check blowby is by doing a compression test. If you check the threads on here, it is explained more in detail. Do a search for "blow by", and you should pull up a few posts we have had. <img border="0" title="" alt="[Wink]" src="wink.gif" />