Thermostat open/close temps

[vms4evr]

Just an interesting little aside on thermostats.
I have a 160deg stat in my car. And the car will actually run at about 165deg with it. This seems reasonable.
Now if I put my 180deg factory stat in the car runs at 195deg +/-2deg.
So I was curious why. I had the factory one on the shelf so I thought I would do a test. The stat is clearly marked as 180, btw.
I suspended it in a pan of water and slowly brought up the temp and monitored it with a thermometer. At 180 the stat showed no sign of opening. At 195 it was wide open and wouldn't open further up to boiling. So this seems like 195 is the magic number to get it to open. Now as I let the water slowly cool down the stat did not fully close until the water reached 180. So it appears the factory stat takes more than 180deg to open.
This might explain why my car likes to run about 193-197 with the factory stat. That is highway cruising I get a constant 193. Yet with the 160deg stat I get a constant 163-165 temp cruising on the highway.
So it would seem the factory stat maybe a little more innacurate or the temp is actually defined by its closing temp, not opening.
Anyway, I thought that was interesting and might explain why most of the LT1 engines tend to sit around 195.
Graham

 

[vettl83]

Graham, could it be that your factory stat is similar to the ZR-1's? They start to open at 180 degrees but are not fully open until 195 degrees. I run a 160 degree stat in the 84 CF with fans on at 200 degrees and off at 190 degrees. Thats where it runs in the summer. In the winter it never sees over 165 degrees with ambient temps below 30 degrees. Makes you wonder. My theory is that stats only controll minimum temperatures. 84 CF 91 ZR-1

 

[sothpaw]

My 160 stat causes coolant temp to stay at 178 F unless it's really
hot out, over 90F. Even as cold as 50 F ambient, coolant was
still at 178 F. Oil will run a little hotter, but only 5-10 degrees once it's warmed up.

 

[WhalePirot]

The thermostats cycle open and closed as normal operation. Some are more accurate than others, but the design and size of the opening is part of the TOTAL cooling picture, too, which includes radiator cooling capability, water pump flow, coolant concentration, adequate airflow through the radiator (blockage and fan 'ON/OFF' temps) and flow through the hoses, which can collapse.

A $4.95 Robert Shaw 330-180 allowed the rest of my coolant components to work effectively, while the Stant did not.

Nice experiment with the stats; a good way to see if one works. Best done with a candy thermometer.