Engine Light and Heat problems

I think my mechanic screwed this up....

I had them replace the timing chain + tensioners.

Shortly afterwards the check engine light would come on and the heat gauge would jump around like crazy. You would see if jump from about half down to cold and back to half instantly. It was like a heat sensor was falling in and out of somewhere.

The check engine light only reported a heat sensor error.

Now my car never shows a temparature......It doesnt even jump around anymore but sits on far left cold.

The reason I thought it was falling in and out was because it would sometimes change when i would accelerate or brake and I figured it was falling back in or out at those times.....

I know this probably isnt an issue but would be nice to have a working sensor/gauge.

it sounds like the mechanic had an air pocket in your cooling system and when the engine would circulate it, it would hit hot/cold spots. you're lucky it didn't cause your head to warp if that's the case. otherwise, you just have a loose wire that was shorting out by connecting/disconnecting to the sensor that would make it jump and throw a code or a bad sensor. my guess would be a loose wire/connection through.

Loose wire gets my vote. An air pocket usually would have found its way to the radiator and the out through the pressure cap.