I use the analog version from NewR3 like Dragger posted the link too. I see it stuck in most oil tanks I happen to glance at, HD's especially. It's a popular dip stick temp gauge.
Had it for couple years now and the oil temp all depends on how long and in what conditions you are operating. It's not like an "inline" temp probe that reads heated oil from the block so for example, the reservoir tank dip stick has been as high as 225F in cases of hot days in Philly traffic. Typically it stays under 200F around 180F-195F at operating temps.