Water Temp Gauge Wiring

[dreabrown]

I'm putting an LS3 into my GenII GTM and I have a question about the wiring of the water temp gauge. The custom harness I got with my engine from SMC Performance connects to coolant temperature gauge just in front of the driver's side valve cover. Can I tap into this gauge wiring for the signal for my dash temp gauge, or does it need it's own sensor? The manual outlines removing a plug and adding a sensor at the base of the engine on the passenger side. Unfortunately I didn't do this step before mounting the starter so its not easily accessible at this point. Not the end of the world if I have to remove the starter and install the sensor, but if I don't have to do this I'd like to avoid it.

Will tapping into the feed from the sensor that it also feeding the ECM harness affect engine controls or the strength of the signal to the dash gauge?

Thanks.

[RumRunner]

I have an LS3 in my GTM Gen2 as well. The LS3 has identical ports for a water temp sensor on the passenger and driver side. I believe the one on the driver's side (toward the front of the car) has a plug in it when it ships from the factory. Just remove the plug and thread in a second temp sensor for your gauge. I used the passenger side port (toward the rear) for my engine computer.

Generally speaking, it is not a good idea to "T" off the temp sensor wire.

-Michael

[LCD Gauges]

The ECM will use the coolant temp for start-up condition parameters which affect start-up quality and idle quality. I tried tapping into the temp sensor wire for the same
reason during an engine swap into an early model sports car.

HP Tuners showed the coolant temperature as half the actual reading. The sensor is resistive so any parallel connection will cause a change in the sensor's ability to output
a proper signal to the computer (resistance in parallel reduces the overall circuit resistance - Ohms law). In the end, I had to install another sensor on the opposite cylinder
head to provide a signal for the in-dash gauge.

There may be ways to make this work if the interior gauge has a very high input resistance, or perhaps there is a wiring technique available for such a need. I'd be interested
to know if your method can be accomplished without the use of a second sensor.

[dreabrown]

Totally missed the additional port on the passenger rear of the engine. I removed the plug and added the sensor.

Its amazing how you can look at this project every day and miss the obvious!

Thanks.

[02scvette]

Thanks for this old post guys! I'll be using the other head port as well.