S13 CA18DE temp reading floats around

[Nissan2nr22]

So I have a 88 silvia qs imported, fully stock.

Im going to take the cluster apart and look at it see if theres any loose grounds wires etc and inspect the connector on the sensor inside the engine bay.

What happens is while im driving the temp will rise to 3/4ths then sometimes 4/4ths and then back to regular temp etc... BUT IF I HIT THE DASH it will jump back to regular temp readings.

The car itself is NOT overheating, checked radiator temps and such etc..... has proper coolant, no water pump noses, pulley spins fine, belts new, thermostats good etc....... I drive with the AC on all the time no problem I just have to flick the cluster or smack the dash a few times by the cluster.

I was wondering if anybody had any ideas or suggestions while I have it apart to look at, maybe someones having the same issue and already fixed it? Share your knowledge please