Temp gauge

[justins81213]

Temp guage will move from cold to normal then drop back to cold. After about 5-10mins of driving it will reach normal operating temp and stay. Could this be the thermostat trying to stick open?

2006 Ford Ranger
3.0 RWD

 

[Dirtman]

That sounds normal to me... engine is cold, warms up, thermostat opens, engine cools, then warms back up. That's how engines work?

If the thermostat was stuck open it would just take forever to warm up.

 

[4.0blue98]

Yep, Mine does that when it's real cold out.

 

[justins81213]

Ok just figured I'd check mines never done that before normally it just slowly moves up to normal and stays. I've never seen mine move all the way up to normal then drop all the way back down to cold. Thanks guys!

 

[RonD]

Could be thermostat is wearing out if its a new "thing" you are noticing for normal driving

T-stat should be a 192-195deg, when coolant gets to 190deg or so, +/- 3deg, t-stat will open a bit and send hot coolant to upper radiator, this causes COLD coolant to come in from lower rad hose to water pump
This can cause a drop in temp gauge if its very COLD coolant, but I wouldn't expect a drop too far, i.e. down to C
But if t-stat was opening too far then yes it would drop alot more

t-stats still use WAX to sense temperature
The wax is in a sealed container, there is a piston and rod at one end of the container
A spring holds t-stat closed
As the wax is heated up it expands and pushes on the piston and rod which overcomes spring pressure to open the t-stat a bit, allowing coolant to flow OUT to upper radiator
As the COLD coolant comes in and circulates it SHOULD cause wax to cool down closing t-stat a bit

This opening and closing "a bit" should reach an equilibrium, operating temp, based on engine use(demand/load), radiator cooling capacity, and outside temp.

It could be the wax is expanding too much, this is a "fail safe" for a t-stat, they are suppose to stick OPEN when they fail, which is much better that staying CLOSED, lol

Or it could also be your Temp Sender is acting up, so t-stat is working fine just the "reporting" of the temp is acting up.

Feel your heater air temp when temp on gauge drops, if heater temp is also dropping then t-stat is opening too far and gauge/sender is correct
If heat feels the same then change sender

 

[justins81213]

Heat drops out to I'll pull the thermostat out and check it. Thanks RonD!