Thermostat Operation?

[Williboy]

Got a stupid question on the correct operation of a thermostat.

When first starting up the car, my old 190* thermo would rise up to temp, drop 20-30* then eventually rise back to 190* after awhile. So after flushing the cooling system and replacing the stat, I now see it rise to 190* temp and then stay there. Then the car is running 200* in 75* weather. I'm thinking the old was was correct and the new one ain't right and I just don't want to pull the thermo housing again.

 

[bubba22349]

From your description your old T Stat was likely sticking some causing the temp functions. However your new T Stat is operating just as it should for best economy and performance you want a steady operating temperature so your good to go. Good luck

 

[Williboy]

I was always under the assumption the old was working correctly. The motor would start to heat up, the thermo would open, allowing a rush of cold water in, temp would drop for a few minutes and then build back up until all the water warmed up slightly and the temperature would stabilize.
Maybe I'm being paranoid, but on a cool day ( 70*+/-) it use to maintain 190*, and then get to 200* on hot days. Now it's running 200* @ 75* after 20 minutes, I'm afraid to see what would happen in 90* stop/go.

 

[bubba22349]

Did the old T-Stat still work correctly? Maybe, but the only way to know is to test it again either by heating it in a pan of water with a thermometer to see its operation or reinstalling it. Actually there shouldn't be a rush of cold water into the engine when the T-Stat fully opens, a 190 T-Stat should start to crack open a little at about 170 degrees, plus with the T-Stat housings bypass the coolant or water is still moving through the engine and radiator at all times whenever the engine is running even if the T-Stat is closed, it's just at a much slower rate. Yes you can see when the T-Stat fully opens with a good temp gauge and there will be a slite drop in temps, though 20 to 30 degrees is excessive and a sign that something isn't working right.

Since you flushed your system out (this maintance should be done anyway every 2 to 3 years), so depending on how dirty the coolant, engine block, head, heater core, and radator, was before as compared to now. The Flushing may have had a bigger effect on the cooling systems operation then changing the T-Stat. Yes for sure the ambient air temps can have quite an effect on the engine operating temps but if your engine is running in the middle of the 190 to 210 operating range this is quite good for economy and performance its what Ford designed the cooling system to do. Good luck

 

[chad]

"...if your engine is running in the middle of the 190 to 210 operating range this is quite good for economy and performance…"
ECHO, Echo, echo

most ele fan 's come on pretty high (215/220*?), U can get thermos. as low as 180*…
it's quite a range ("too cold" not good for econ/perform as well as "too hi").

 

[thesameguy]

Thermostats aren't supposed to be an open or closed affair - they can also open partially. Proper behavior would be to start opening at their specified temperature and then becoming fully open around 10-15 degrees later. As such, you should hit a target temperature then slowly open flow the radiator, maintaining a constant temperature. A sudden drop in temperature suggests a sticking thermostat that goes from full closed to full open suddenly instead of gradually.

 

[Williboy]

Thanks for all the help, it does makes more sense opening slowly. In the last year I have everything from valve stems fouling plugs to a pertronics failure to a blown freeze plug. I guess I was just getting paranoid driving it around.
Time to stop worrying and enjoy the ride!!!

Thanks!!!!

 

[wsa111]

A good test to make sure the thermostat is opening all the way is submerse it in boiling water to see if it opens the full length of its travel.
Also if your thermostat does not have a bleed hole, drill a .030" hole and upon installation make sure the orifice is at the 12:00 position.

 

[Econoline]

If you are having thermostat issues or change the stat b/c you think you may be having thermostat issues, test the new one. Test the old one. Watch the thermometer and heat the water slow. Otherwise your stabbing in the dark.

The fluctuations are after flushing the cooling system and changing the stat. So what you are seeing is related to one or both of those things.