Engine Coolant Temperature Gauge question

[syljay]

Today, I checked the coolant temps on my 88 5kq in the same fashion as 
on the 90 100Q - - with the cooking thermostat probe taped to the 
upper hose and insulated.

Here is the comparison table:

Engine start, idle at 1500RPM

			  Upper hose temps
Time    Gauge reading   90-100Q  	88-5k8

00:00    Below 1        25F		27
02:00	--		--		36
03:30	--		--		43
04:00    "        	25F		--
05:00	--		--		66
07:00    0.8      	36F		93
10:00    1        	60F		111
12:00    2        	81F		126
13:00	--		--		138
15:00    3        	90F		155
19:00    4        	144F		170
21:00    4.5      	160F		175
24:00    5        	172F		174
26:00    5        	176F		176
27:00    5        	178F		176
28:00    5        	180F		176
29:00    5        	180F		176
30:00    5        	180F		176
31:01    5        	180F 		176


You can see that the temps on the 5kq rose up a lot quicker than on 
the 100Q. A stuck open thermostat would account for the slow temp rise 
on the 100Q. An open thermostat would also account for the wide swings 
on the temp gauge for city driving vs highway driving.


I took the 5kq for a ride and observed the coolant temp gauge. It was 
  steady all the time.
The total variation between city slow driving(max heat) and coasting 
in neutral down a highway hill at 65 mph(max cooling) was maybe 1/8" 
on the gauge.

I got a new Wahler thermostat(035 121 113 B, 87C) today. Of course, I 
had to test it out in a pot of water on the stove. :-)
You can see the hysteresis loop in the table - it opens at 194, but 
closes at 187.

Opening		Deg F	Closing

Closed		187	Closed
"		189	small crack
"		190	1/16
"		192	- 1/8
small crack	194	1/8
1/32		196	1/8
1/16		198	3/16
1/8		199	3/16
3/16		201	3/16
Full OPen	203	Full open



SJ in NJ