this gives you a general idea of how it is checked. i change mine at the recommended 40k interval so i havent checked inbetween changes ever. others may chime in but honestly if youve never changed it and it has more than 40,000 miles you should be doing that instead. if it was recently serviced and you think you lost fluid or just absolutely must check, my understanding is once up to temp with the drain plug removed you want to see a drip or two but no stream. essentially no drip is perfect but that could also mean its underfilled. at this point you are left with the option of adding fluid and seeing what, if anything, comes out which brings me full circle to; if you begin to add more than maybe a 1/2 quart you may aswell change it. i am no pro so you may get pro insight but this seems to be the general consenus...