View Full Version : engine temp guage reads cold

05-28-2012, 09:08 PM
'93 Lt-1 prostar with 2 new t-stats (143 and 160 from BAWS)

Ran the boat for 1/2 hour and the temp still reads below 120. Then we idled for a few minutes and the temp read 160. Ran it up to 30 mph and temp read below 120 again. Tried to idle again but temp stayed down below 120.

I'm wondering if a have a bad temp sensor. Is it at the front of the engine near the mixing block with a single wire on it? That block feels very cold even after running 1/2 hour. How do I check to see if the guage is ok? Ground the wire to the block and watch guage move?

Engine runs great and does not seem to be running hot. I just want to make sure I'm looking at the correct sensor for the guage. Thanks.

05-28-2012, 09:09 PM
Sensor that I am asking about is in pic just below spark arrestor, brass color.


05-28-2012, 09:29 PM
engine too clean...cooling off too fast :D.... yes I would check sensor...they are cheap...

06-04-2012, 08:32 PM
I'm having similar issues Dave with my '94 Prostar with LT1. I'm sure you know there are two temp sensors on the LT1. One for the gauge and one for the ECM. The one for the gauge has a single tan wire coming off it. The other one to the right with two wires is the ECM sensor.

If you ground the tan wire it just pegs the needle on the gauge. This only tests out if the gauge is active or not. I've resorted to pulling the gauge temp sensor and putting it in a pan of hot water to test it out. The sensor is just a thermistor to ground from the gauge. Inverse relationship to temperature. The higher the temp, the lower the resistance. That's why a dead short to ground pegs the needle.

It's kind of a pain but you can leave the tan wire attached, immerse the bottom half of the sensor in the pan of hot water with a meat thermometer in it, and then touch a ground wire to the body of the sensor to complete the circuit. Keep the tan wire connection out of the water and give the sensor some time to heat up. Compare the gauge reading with the meat thermometer. It's not exact but it gives you an idea if the sensor is in the ball park or if the problem is elsewhere.