Oil temp?

As a general rule, how hot should my oil get? My engine runs between 180-210 but pretty much stays dead on 180 when driving. I came back from driving and let it cool down a bit with the fan on then remembered to check my oil temp. I checked it, then started it and on the filter I got the highest reading, it went to 230 within a minute of re starting it. I'm thinking this may be getting my oil too thin and I need to run a cooler. Running 20-50 at the moment.