I have a 1991 honda civic DX. My temperature gauge is usually sitting at the middle of the gauge. However, when I do a hard acceleration or go over bumps (speed bumps, potholes, gaps on bridges etc...) on road, the temp gauge DROPS to bottom of the gauge and climbs back up. Does anyone know what I need to do to fix this problem? Many Thanks.

 

It's a loose wire. If the circuit opens the gauge will drop to cold. The sender is screwed into the head under the distributor toward the back of the engine with one wire on it. Make sure that plug is tight. It could also be the wiring behind the cluster, or the gauge itself.

If the whole cluster loses power the gauge will also drop. That's hard to tell because all the warning lights are normally out, and the gas gauge will stay where it last was when the power fails. To test that, you could jump the switch on the brake fluid reservoir, which will cause the BRAKE light to stay on all the time. It's powered from the same place. See if it goes out when the gauge drops.