Living in Fl. we see summertime temps. above 95* most days. When riding in traffic oil temps. can go above 250* without a cooler. I have a 94FLSTC and have run an HD oil cooler since the first summer I had it and riding in traffic the temp. does not go above 210*. This is measured with the oil temp dip stick in the oil bag. I have two of these (temp sticks) and they read the same, so I'm guessing that while I have not had them calibrated to a standard they are pretty close. On my 05FLTRI I but the oil cooler on the second day I had it and have not seen the temp. go above 210* sitting in traffic (but I don't sit in traffic much). This is measured with an in tank sender and faring mounted guage (aftermarket). The way I see it if you can keep your oil cooler for $200 to $300 it is money well spent. FLSTC-155,00mi+ before HD remanuf, FLTRI-60,000+ and running strong.