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!

Tested out a 6" Lucite lower radiator block tonight and it did pretty good.
On the freeway with FAN OFF it ran 80 oil and 80 water.
In the city playing a bit and with the FAN ON it ran 90 oil and 80 water.
I will use the block for long cool road trips, it slips on and off in about 30 seconds.

Oil temp still too low.

Bruce, how could I raise my oil temp?
I don't have a oil cooler.:confused:

Even with a cooler with a thermostatic adapter (which won't help if the oil temp is too cool to begin with), I don't know without raising your coolant temperature.

Have you checked the location of your oil sending unit? If it is not in direct contact(immersed) in the oil your temp reading will be off and not accurate.

Mine from the builder was off and was reading quite low as it wasn't in contact with the oil, fixed this and temp went up to proper operating temps.

Temp in C and F
 

Is there some confusion here? Many Cobra gauges, in order to be more "classic" are set up in Centigrade. So 100C=212F. A 70C engine temp is a little low, but not as an opening point for a thermostat. A 70C oil temp is also a little low assuming you have fully warmed up and the ambient temp is above 35C. A sandwich thermostat on the oil cooler can help here. Raising the engine thermostat rating will tend to raise the opening temp, and tend to keep the engine temp higher overall. Using the thermostat to set a specific point in operating temp is a lot of bother when the range of cold (70C) to very hot (110C) is 40C.
Gauge watching is one reason most production temps are centered weighted at the mid point of the "good range" for the car. The motion may also be damped at the center (as BMW does).
If you are racing it makes a big difference. If you commute a lot, oil temp can make a big difference in avoiding cold oil sludge problems.
Otherwise...relax and drive like you stole it.:LOL:

Yep, this is what I would do before trying to block off the radiator.