Engine Coolant Temperature Gauge question

[syljay]

I took temperature readings of the engine coolant.
I used an Electronic baking thermometer which was checked against 
another electronic thermometer. The two thermometers were within 1 or 
2 degrees of each other at various temperature readings.

I wanted to see what the coolant temp vs time readings were, and how 
the radiator fan switched on and off during this period.

Outdoor temp = 25F
Thermometer probe taped to upper radiator hose, and then the hose was 
wrapped several times in fiberglass pipe insulation.

instrument temp gauge markings are:
|||  |  |  |  |  |
C                H

123  4  5  6  7  8

Engine start, idle at 1500RPM

Time	Gauge reading	hose temp

00:00	Below 1		25F
04:00	"		25F	Heating fan kicked in
07:00	0.8		36F
10:00	1		60F
12:00	2		81F
15:00	3		90F
19:00	4		144F
21:00	4.5		160F
24:00	5		172F	Cooling fan kicked in and shut off after about 4 seconds
26:00	5		176F	Cooling fan kicked in and shut off after about 3 seconds
27:00	5		178F	"
28:00	5		180F	"
29:00	5		180F	"
30:00	5		180F	"
31:01	5		180F	" 	


The number 5 position on the gauge is about 2/5 of the way across the 
dial. Halfway across would be at about 6.

Observations:
It seems strange that the fan radiator fan should be kicking in when 
the coolant temp is only at 180F.
Bentley says the thermostat begins to open at 188F, and is fully open 
at 215F. And, the thermoswitch for the radiator fan switches on at 
190-200F.

According to the above data, the fan can switch on before the 
thermostat is fully open. I thought the thermostat was the MAIN 
coolant regulating mechanism, and the fan switched on ONLY after the 
thermostat was fully open already and the temp was still rising. But, 
according to these numbers, the fan is doing the cooling before the 
thermostat has fully opened. Thats a lot of wear and tear on the fan 
motor if its running when it doesnt have to.

Oh wait! The fan switch is located at the bottom end of the radiator, 
where the coolant would be cooler than at the top of the radiator 
where the upper hose is. So, a 190F switch trigger point would be 
equivalent to something like a 200F, or higher, upper hose temperature.

When I have time, I'll take out the thermostat and the fan switch and 
then test them together in a pot of water to see which opens when and 
at what temperature. Something funny goin on here.

Another thing, it takes almost 30 minutes to get to 180F. Thats a bit 
long, no?

SJ in NJ