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Discussion Starter #1
I recently picked up a 1967 GTO with a 1970 (i believe) Pontiac 455. It was a frame off restoration. Most of my mechanical skills have been to replace the oil and filter.

Driving it the other day with the temperature 90+ degrees in stop and go traffic, the temperature climbed up and hit 250 on the temperature gauge. The dash gauges are either original or reproductions. Lowest temp, 100 Middle 210 and high is 250. Graduations in-between those which would be 155 and 230.

Today, I flushed the coolant out and replaced it. Tested it and measured with a pretty accurate infrared thermometer to see when the thermostat would open. It opened when the temperature (infrared measured) was a bit higher than 160. I was looking at the dash gauge every few seconds and noticed when the infrared measured 150-160, the gauge measured about 210. The dash gauged climbed all the way and pegged 250. At that time I infrared measured both sides of the thermostat and the reading was close to 180. At that point I felt the radiator get hot and when I looked back at the dash gauge, it was coming down from 250 to settle around 210.

So, I'm looking at some aftermarket gauges. Something like these.
1964-73 GTO Autometer Gauges, Autogage 2-5/8" White black holder @ OPGI.com

Do the gauges like I linked above come with sensors? Are there different sizes or are they standard sizes. If they come with sensors it appears I can either replace the one where it is now or is that another place to the left of the thermostat where I can place a new one?

Here is a photo of my thermostat.
 

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Generally those gages come with a sensor bulb and threaded fittings that go right back in where your existing electrical sensor is, or you can use the other bung (threaded hole) and leave the stock one in place. You might find the 2.5/8" gages a little big - I also ordered them at one point and they blocked most of the view of my right foot and gas pedal, I returned them and like the 2.1/16" size much better.

http://www.summitracing.com/parts/atm-2397
 

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Discussion Starter #3
Good suggestion on the 2 1/16 gauges. I took a compass and drew 3 at the larger size and 3 at the smaller size and I think I'll like the 2 1/16 size better.

Anyone know if the gauges swappable? Meaning can I move the gauges around so I'd see engine temp on the left, then oil pressure and lastly on the right, voltage?
 

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I was able to get the temperature gauge reading calibrated on my original '65 GTO rally cluster by talking to Pete Serio. He referred me to Lectric Limited, which has the correct value temp sensor for our Pontiacs. I had been running a generic NAPA unit, and the reading was 20 degrees too high over actual temperature. Installing the correct sending unit fixed the problem. The car now runs 180-195, instead of the previously indicated 200+. Also, dash grounds can affect the gauge readings. A bad or weak ground will make them read much higher, especially with the headlights on.
 
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