Engine temperature up and down

[dalola]

Correct. And in extreme cold & low load driving, the thermostat will cycle much slower. There is also a small percentage of coolant bypass, for HVAC performance.

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[Mikk]

Fx4 Eco: Engine temperature gauge keeps going from 4 to 3 sticks and vice versa every minute or so while driving, anyone also has this issue ?

I had this happen on a brand-new Escort back in the 90's. The dealer replaced the thermostat and the problem went away.