I use an infra-red temp gun..... just cost a few bucks. Head temp will be the hottest, so measure there. Anything over 275 and oil starts to break down..(dino oil). Synthetic is known for not breaking down because of heat. If you want to make sure your oil is still good, start fresh, run it like you always do, change the oil after 1,000 miles and take a sample. Blackstone-labs.com will send you a kit for free... you pay $25 for a basic analysis, $35 for a full sample. Get the $35... you will not only know how good your oil is working, but how long you can expect it to last until the next oil change. Generally speaking, your bike will not ever get above 275 head temp ... I've been sampling my oil for many years in all my vehicles.... you will be surprised how long oil will last in today's motors. I change my oil in most of my vehicles every six months, and sometimes longer. I'm just doing what the doctor recommends..!