[vettestr]

Dan, The fan on/off points are not the issue. If your fan was on the moment you started the engine the t-stat should still hold a closed system until the opening point of the t-stat, you verified at 180*. Then colder coolant would enter engine side of t-stat (so you would see eng temp drop). Repeating this cycle over and over but with radiator side coolant now warmer than 1st cold start cycle. IF YOUR system was very very efficient you would see gauge swinging between colder coolant (maybe 150* too t-stat set point of 180*). Your complaint was just staying at 160* on gauge but have a 180* t-stat. Does it swing?

I would look for something bypassing t-stat or not having a true CLOSED system. The w pump always moves coolant in block and heads but when t-stat opens it exchanges engine side coolant with rad. side coolant, then it closes and moves coolant on engine side only and this cycle continues. T-stat is not an instant open /close devise but it should seal when closed. The short hose between pump and intake promotes additional flow in the cyl. heads but remains on the engine side of the t-stat. Monitor temp in rad. at COLD start up .... if temp creeps up before t-stat opens first time SOMETHING is bypassing the t-stats closed side of the engine. Then you have to find it!