how cold is too cold for oil temps?

Waynezworld

I'm a little confused...if the oil temperature sensor is sensing the sump temperature a car with no oil cooler is obviously supplying close to the same temperature oil to the engine for lubrication. However, in the instance where an oil cooler is installed wouldn't the actual oil supply temperature to the engine be unknown without measuring it at the cooler outlet? It would seem to be logical that the desired temperature in the sump would be relative to the temperature drop across the oil cooler. Is the 180-220 that everyone recommends assuming some theoretical temperature drop across the cooler? If so, this would depend on cooler size, ambient temperature and engine loading. Wouldn't it be normal for oil temperature to read 20-40 degrees higher at the sump due to the effect of oil being heated up as it flows through the engine? It seems to me that the temperature of the oil being supplied to the engine should be the critical parameter or am I missing something? I guess the question I'd ask is what is the ideal supply temperature for oil supply/optimum lubrication/minimum wear? If the answer is in the neighborhood of 180 to 220, it appears to me that sump temperature of 180 opening the oil thermostat (assuming one is installed) will result in keeping the oil too cold during cooler weather and when driving like grandma. If the thermostat keeps the oil in the sump at 180 to 200 wouldn't that mean that the oil out of the cooler/supply to the engine would be significantly cooler and if so, is that acceptable? Just want to make sure I'm not missing something and have all the facts for sizing my cooler properly. Thanks!