Water Temp Gauge Acting Up Options

[HardHead93]

I have a 5sfte with a DIYPNP standalone ECU. My water temperature gauge started acting up recently. When I turn the key to the on position (car not started and cold) the needle goes all the way to hot. Then when I start the car it drops all the way to cold and stays there. When I get the water temp reading off my ECU it shows the temperature as normal when the car is fully warmed up so this looks to be some type of problem with the water temp sender, wire, or gauge. I have replaced the water temp sender with a brand new one and the problem is still the same. I have looked at the factory wiring diagrams and it looks like the water temp sender (different from the water temperature sensor) is wired directly to the gauge (no ECU connections) and is grounded at the intake manifold. I do not feel comfortable driving the car with no insight into how the car's temperature is performing and I do not want to have to have a laptop plugged into the ECU all the time to get that information. What would be the best way to test the wire and gauge to determine the problem? Has anyone experienced this problem?

[Box]

Sorry just now saw this for some reason. There are two coolant temp sensors, one for the ECU and one for the gauge.

Scratch that just reread where you replaced it. If it's any consolation the gauge in the car is a dummy gauge and by the time it hits hot it's too late, I'd get a good aftermarket gauge to use then you can have absolute piece of mind.

This post has been edited by Box: Aug 20, 2016 - 7:19 PM

[HardHead93]

Sorry just now saw this for some reason. There are two coolant temp sensors, one for the ECU and one for the gauge.

Scratch that just reread where you replaced it. If it's any consolation the gauge in the car is a dummy gauge and by the time it hits hot it's too late, I'd get a good aftermarket gauge to use then you can have absolute piece of mind.

I was thinking the same thing. I have a spare gauge cluster, if I cannot get it to work when I swap the temp gauge into it, I think I will add an aftermarket one.