thermostat behavior

[Amopower]

I see various threads on here that act like a bouncing temperature gauge is not normal. For my case, my gauge goes from 2/3 back down to 1/4...then back up again and the cycle repeats. I thought that would be normal behavior though? The temp gets to a certain point, then the thermostat opens, and the colder fluid comes in, cooling things down. Then it closes again and the coolant warms up, and the cycle repeats. Why is the moving needle considered not normal?

 

[DeRocha]

I see various threads on here that act like a bouncing temperature gauge is not normal. For my case, my gauge goes from 2/3 back down to 1/4...then back up again and the cycle repeats. I thought that would be normal behavior though? The temp gets to a certain point, then the thermostat opens, and the colder fluid comes in, cooling things down. Then it closes again and the coolant warms up, and the cycle repeats. Why is the moving needle considered not normal?

Ideally the thermostat should open and close slowly to keep the temperature swings to a minimum. The thermostat isn't 100% on or off, rather it should be variable as the thermostat reaches it set point. This variability is due to the way the T-stat spring expands and contracts with changes in temp.

 

[Anime]

It depends on the thermostat. I've had some where the needle goes halfway and stays there, and others where it goes up, then down when it opens, then back up, and still others where it goes up then down then back up, then down, etc. And these are all OEM part number Motorcraft 'stats. There's even more difference when you get into aftermarket stuff.

It's not really a problem unless the 'stat is stuck open or closed and the engine is either getting too hot or never reaching operating temp.

 

[mikeinri]

I totally agree. A moving temp gauge isn't a problem (unless it's overheating), and the colder it is outside, the more movement you will see, especially after first starting it up with a cold engine.

Hope this helps.

Mike

 

[marragtop]

How long has it been fluctuating like that? If it has changed since you bought the truck then I would replace the Tstat. If it's acting up, and it sticks closed, it may cost you a motor or head gaskets.

 

[Masterd]

My brand new T-Stat does that...its normal.

It opens once the motor hits 190*....

Closes partially or fully below 190*...

 

[DeRocha]

How long has it been fluctuating like that? If it has changed since you bought the truck then I would replace the Tstat. If it's acting up, and it sticks closed, it may cost you a motor or head gaskets.

Exactly.. If the T-stat has always fluctuated like that then leave it alone. If however it just starting behaving like this it means you T-stat is worn and not operating freely and will eventually get stuck in an open or closed position.

 

[mikeinri]

Good point guys. Another thing to consider (though much less likely) is a problem with the sensor, gauge or wiring. Again, only if this is a recent development, and only if replacing the t-stat doesn't fix it.

Mike

 

[Robrt32]

Mine done it when i first got it so i replaced the thermostat and it still done it.... It never tries to run hot at all so i chalked it up as normal..I have always paid close attention to my gauges , operating heavy equipment all my life has me trained to do so