Originally Posted by Modshack

I was confused about this too until I researched it. Thermo plates are ALWAYS circulating some oil. This is to avoid the thermal shock of a Thermostat opening fully at 180 degrees into a cold cooler core. As the temp hits the trigger point More oil goes to the plate and less through the bypass (which is naturally the path of least resistance). So basically, the cooler is always functioning at some level, just more so when the oil is hot and more fluid is diverted through it as determined by the thermostat. This is why a cooler starts getting warm (with a thermostat) as soon as the engine is started, and why the oil may not get up to temp in cold situations. This reinforces the need to properly size the cooler. More is not better unless you have track needs like Resipsa and then you have to make some special accommodations (blocking part of ther core) for normal street use.. Putting a Large "race" cooler on a car with no thermostat would be problematic in cooler climes.