Temp gauge issues

Good morning,
I have a question I hope someone can answer for me. I have a 350 cubic inch Chevy with 150 hours on it, when running along at 3000 rpm's the temp gauge is showing 190 degrees. If I use an IR gun to check the temp it shows 149 degrees where the sending unit is and 170 on the coolant tank. The gauge is a teleflex brand. It has done this since I installed the engine. Thanks in advance for any and all ideas.

You have to remember, when you use your IR gun, you get some drop off in temp (and some inaccuracy) depending on how far away you are, and when you measure the external portion of the housing, that is exposed to air and heat dissipation, you're not measuring the same thing as the internal coolant.

190 is a safe operating temp, if you want it to run cooler, you can try a 160 thermostat. If you're simply dismayed about the IR gauge reading differently than the gauge, I believe you'll always be dismayed. The two measure differently, and measure different items (coolant vs coolant housing). I do not believe you'll ever get those two to jive perfectly.

I lean towards a dual station sending unit being provided instead of the single station sending unit...

I'm not sure what you are getting at Mark, why duel station?

That's what I think you were given....assuming your observations are accurate, its a plausible explanation for how things are behaving.

if you are handy with electronics, I believe I can describe an experiment to prove out the theory...if you are interested...

Teach me! I am willing to try it. And thanks

you need a variable resistor (potentiometer - 250 or 500 ohm), a pair of jumper leads on the variable resistor (1 on a 'fixed' end & 1 on the wiper), and an ohm meter.

start engine and bring it up to temp. disconnect temp sender (at engine is best) and measure resistance from sender terminal to ground. connect ohm meter to variable resistor and adjust it to have same resistance just measured at sender. without touching the adjusting knob, connect the variable resistor between the sending unit and the gauge...and see how much lower the temp is on the gauge...if engine has cooled you can restart it.

The idea is the dual station sender allows twice the current flow, at a given temperature, as the single station unit...measuring the sender's resistance and then adding it (in series with the sender) will "recalibrate" the sender's output to be like a single station unit at that temperature...

Eyeballing some old data I had suggested a 2X factor in the resistance change between indicated temps of 145 and 190 deg F....

if you have access to fixed resistors, you can use them in place of the potentiometer...

Thanks Mark, I have a brother who will help me with this and maybe i can get to the bottom of the mystery.

You can indirectly blame the sending unit by checking the gauge....not fool proof but reasonable...the process is:

remove S wire from gauge, power on and connect 110 ohm resistor between S and GND terminals - gauge should go to half scale.
Repeat using 33 ohm resistor; gauge to Full Scale.
Repeat using 240 ohm resistor, gauge should go to min scale reading...