[font='Times New Roman']I just installed an electrical water temp gauge from auto meter. The gauge reads correctly when the car is idling. Once I start driving the needle starts jumping around. The thing looks like a boost gauge. Any Ideas what could be causing the problem? I am assuming it is a grounding problem but not sure. Any help would be appreciated. [/font]

 

Where is your temp sender mounted?

 

I replaced the breather valve with an autometer 1 1/4 hose coupler. So the sender is directly in the middle of the intercooler. The sender does stick up a bit close to the intercooler.

 

Make sure that the sender connection does not touch the intercooler when the engine moves around. Also, since the sender is not mounted in the head or block, and in the water stream after the thermostat instead, you should expect some fluctuations in temperature from the thermostat opening and closing as it tries to keep the engine temperature constant. Unlike water flow in the engine itself, that which flows towards the radiator is not a constant flow at all temps, and will tend to vary widely.

The above flow issues make the gauge move relatively slowly and with only a medium amount of overall range at a time. If your gauge is swinging wildly, say from 'zero' or whatever the minimum is (usually 100F) to a normal reading and repeating, then you most likely have a grounding issue. Since there is no engine ground where the sender is attached, you end up needing to run a separate ground. Make sure this is very firmly attached at the sender and then connected to a good ground, preferably to where other electrical grounds collect (on either frame rail behind the bumper are good, look for a lot of brown wires). Likewise, make sure that the gauge itself is getting a good ground as well as power source.