Electric temp. gauge

[CliffS]

My elec. Autometer reads like 10 to 15 degrees to high, the higher the temp. the bigger the difference with the actual temp. Will a mechanical gauge solve this/ be more preciese?

[ProBell]

How do you know the actual temp? If the gauge is not working call Autometer, they have helped me in the past at no cost. Randy

[CliffS]

Randy, I'm using a laser pyrometer to check temp. After installing the electric gauge the reading were quite off. Since I'm overseas I don't think Autometer will do something about it.

[zbugger]

Where is the sender and where are you reading the temp from?

[CarlC]

Try putting a 100 ohm variable resistor/trim potentiometer in series with the sending unit wire. Adjust the trim pot until the temperature reads correctly. You can either leave the trim pot in place or buy/make a resistor pack to replace it.

[CliffS]

Where is the sender and where are you reading the temp from?

Sender is located in front of intake manifold next to the thermostat housing.

[CliffS]

Try putting a 100 ohm variable resistor/trim potentiometer in series with the sending unit wire. Adjust the trim pot until the temperature reads correctly. You can either leave the trim pot in place or buy/make a resistor pack to replace it.

Thanks Carl,

I'm not an electric wizard but will ask one of my buddies to take a look at it.

[zbugger]

Sender is located in front of intake manifold next to the thermostat housing.

Cool, but where are you taking the reading from with the temp gun? Oh, and what is the engine temp reading? At the guage and where you're reading it from.

[CliffS]

Cool, but where are you taking the reading from with the temp gun? Oh, and what is the engine temp reading? At the guage and where you're reading it from.

I'm taking the reading from the manifold just next to the sender unit. For intance: 205 on the gun 220 on the gauge.

[vcho455]

You did not state what the temp was when it was 10 to 15 degrees off. At 180 degrees 18 degrees is 10% off. Is your infrared a $100 unit or a $500 unit? The difference in the price is in the accuracy. The low dollar units often will only give accuracy with in 10% to 20%. You could be looking at a temp guage that is 5% low and a infrared reading that is 5% high. Classic case of tolerance stacking. Also, you are reading the surface temp of the manifold not the temperature of the fluid. The water in the manifold is a swirling mixture of differant temperatures as the water combines in the crossover to the thermostat. The sensor responds to these changes slowly averageing them out. The surface of the manifold is exposed to the cooler out side air which tends to cool the surface of the manifold. And, not to get to deep into the subject,there is a boundary layer in the water passage that insulates the manifold from the hotter water flowing in the manifold. If your really concerned about the temperature you can take a another measurement of the water directly in the radiator. Just a a side note I've seen more engines ruined by bad tachs than by bad temp guages.

[CliffS]

You're right about the temp. of the intake manifold being cooler than the water inside. I used a $90 laser and it's not measuring the water. I found out the gauge is reading correct, Autometer sent me a new sender which gave me the same temps and resistance on the sender. I checked timing, carb, plugs (gapped correct), guess I have to look for someting else....

[David Pozzi]

I've pointed an infrared gun at different things and found it to read about 10 deg lower than internal temps. Outside temp is always lower than internal. I had a pyrometer in a can of boiling water and tested the outside with the Infrared gun, - lower.

[ProBell]

Thanks for the info, that is a good thing to remember, Randy