Thermostat needle

when i give my car gas the thermostat needle goes down, when i get to a steady speed it goes back to normal, what can be wrong here?

Make, Model, Model-Year ?

How many miles on this car(?) ?

If I had to guess, I would say your thermostat is one of the newer ones that, when it fails, stays in the “open” position.

Well, its hard to say very much at all knowing absolutely nothing about the car, its age, mileage, etc. One thing I can say which would go with Whitey’s comment above is that your water pump is likely to be driven by the engine. The faster the engine revs the faster it pumps coolant through, the faster it cools off. When the engine slows, the water pump slows.

If this is a new issue then just take the car for cooling system service. Few things can kill an engine faster than cooling system problems.