IMHO, 165° is too warm for the conditions. With the lake temp at 65° ish, the temp should be ~130-140°. My 454, logs and snails, wouldn't register on the gauge if the valve was wide open.
Could the logs have sand/blockage also?
By the way, you can nearly keep your hand on the tstat housing at 140°.
At 180°, about 2 seconds.
I'd say keep looking.
Dan'l