So let me make sure I understand correctly...Even with the thermostat your
oil is still not even getting up to 180*?? Trust me, the internal leak in the thermostat is not big enough to 'cool' the
oil to the point where the
oil shouldn't warm up. If this is the case, I'm say that your engine is not producing enough heat under normal conditions to even get the oil warm enough for the thermostat to start to work, which is very, very possible. When you really run it, things can change.
Keep this in mind too. Water temp has absolutely no bearing what so ever on oil temp. Period. (unless you have a water/oil cooler of course)
My truck BTW has a water/oil cooler and my oil runs right around 90-100* above ambient outside air temp all year long. It's very common in winter to never see anything above 145 on the gauge. (yes,I have an oil temp gauge in my truck)
Hope this helps.