Dean2, thank you for the question.
Because the transfer of heat is so slow in oil and cast iron, it takes a longer period of time for the transfer to happen.
As you are familiar with AGS operation, you are aware the shutters stay close to approximately 220-225 degrees F, and then open for a very short time until the coolant temperature drops to approximately 190 F. I reason this because it will take time for the the thermostats to catch up to the radiator temperature decrease. The actual amount of time needed to transfer the heat from the oil to the water jacket is only fractional. My guess, it is 1/10th of the the operating time. This is calculated by observing the temperature fluctuated on the temperature gage.
Oil temperature mostly controlled by water jacket temperature as you know.
As an example, if water temperature remains at approximately 225 F, the shutters will never open. The engine thermostat would be wide open since the operating temperature of a thermostat is approximately 205F.
So let’s use an acceptable number of oil temperature normal operating range can be up to 25-30 degrees higher than than water jacket temperature.
If that is the case in this scenario, the oil temperature would remain at 250-255F under loaded conditions.
In the same scenario, the water jacket may get as high 205F, the oil temperatures would be 225-230F. I think fully reasonable temperatures for oil.
Is 250-255 F oil temperature acceptable? Well, I am not a fan of that, however it is still within limits.
One of the things you mentioned is that the shutters are fully open when the engine gets to operating temperature. Well, yes and no. The shutters open and the temperature coolant drops quickly to about 190F. The shutters quickly close again until the engine gets to approximately 220-225 again. The transition time from shutter closing to opening again is the problem for engine oil. Again, the short time the shutters are open is not sufficient to reduce oil temperature enough. Just because the coolant sensing unit is reading at one part of the water jacket, it does not mean another area of the water jacket has the same temperature.
Addtionally, if you look at people’s past comments about removing the shutters, they all say oil temperatures are lowered.