sounds like the oil temps indicate the oil is overcooled. Oil temp should be above 212'F to burn off water in the oil that gathers from condensation inside the block and below 250/275'F to avoid thermal breakdown. I have the issue with my Mustang without an oil cooler, but 7 quarts of oil, that the car needs to be run very hard to get enough oil temp to burn off the water. With the Fiesta, I monitor oil temps and not coolant temp with the Accessport. I tend to be running just above water boiling temp as a maximum, with 225'F-ish on hot days when running hard. This is on the low end of the temp range for the oil. I would not do an oil cooler upgrade on my Fiesta and need to find a way to keep the oil and water hotter in my Mustang. I can barely get the 180'F thermostat to open on the Mustang due to the cooling system I put together. What makes the car run overcooled is the combination of a large capacity oil pan and the radiator being sealed to the front bumper. I have actually started to unseal the radiator and block off anywhere from 25%-50% of the radiator on the street just to get the thermostat to open. Unless you are seeing constant temps above 275'F, I don't see a reason for an oil cooler. If you do go for a cooler, make sure it has a thermostat that will only open when needed.