[gto65conv]

After 20 yrs of staring at dormant OEM rally gauges I'm ditching the under dash and trying to activate them, originally a warning light car. Installed a Standard TS6 sender and the gauge nearly pegged at 160+ degrees. The sender resistance is close to an aftermarket sender I have on another car, I've read Pete's comment that gauges deteriorate over time. Seems like I recall the 64-5 gauges have a different range than later years? So, what are the ranges for these gauges? Do I need a different sender?

[Geoff]

Ames catalog lists the same temp sending unit for rally gauge cars, 1965-72.

[gto65conv]

I looked at the repo units, you're correct below that they show a universal 65-72. Thanks.

[gto65conv]

Here is what I received from Standard FWIW

[Peter Serio]

The 65 and 66 GTO temperature gauges are wound (these are 12 volt DC electromagnet style gauges) differently than later year factory GM car gauges due to the fact that the 65-66 GTO temp gauge is labeled 180 degrees at the 1/2 scale line. My thought is: the makers of aftermarket senders are not aware of this since the car has not been used for everyday transportation in a very long time. Modern off the shelf replacement senders will cause 65 and 66 gauges to read untrue. Typically 25 or 30 degrees higher on the dial that actual. In some cases a brand new TS6 from NAPA, for example, will cause a '65 or 66 GTO temp gauge to "peg" at around 180 to 185 degrees actual coolant temperature.


These old gauges also exhaust their buffering fluid (after 50+ years) and very often are out of calibration due to age. So no matter what sender you try that gauge will not give you a true reading. I can rebuild these gauges in many cases. I also test them using heated water, a thermometer and a 12 volt battery with jumper wires. One of my specialties is automotive electrical.

You can't go by the listings in a parts catalog on parts such as a temperature sender. The aftermarket does not know how to make them for 1960s GM cars as GM changed the # of wire winding over the years as per the markings on the dial. The molded nylon insulated structure of this gauge was used to wind many different gauges for a time span of almost 30 years of cars & trucks.

[gto65conv]

I haven't progressed that far yet but will the oil pressure gauge be a similar conundrum?

[Peter Serio]

Most likely yes. The gauges from that era all share a common nylon core. Inside the nylon AC Delco designed a 100% lint dust and dirt free chamber. I am thinking they did that so the gauge would never stick or bind. Say the car sits for years not driven GM did not want any of their factory gauges to "freeze" in place. Also driving in the desert or wind from the road surfaces off of the freeways picking up fine dust.

The nylon core can be wound as need be to create a fuel, oil pressure or temperature gauge. Differences being length of wire, wire diameter and # of turns. Also the direction of turns per length of wire. The engineers did math on what they wanted to determine length of wire and direction, number of turns per. I believe that the math was probably done on a slide rule back then.

Inside of the chamber before they put the 2 halves of nylon together they added 2 or 3 drops of glycerin. That serves 2 purposes: A) it acts as a lubricant and, B) it gives reaction of the gauge a small cushion so that the Coolant temperature and Oil pressure gauges both read in real time with a 1 to 1 & 1/2 second delay. This cushion is what disappears after many years, or if the car sits outside in the sun. You have to have the cushion of fluid inside or else the gauge will get out of calibration all by itself.

This is a very common issue with 1960s and 1970s GM gauges; almost every one I am sent for repair is missing it's original glycerin.

[gto65conv]

Excellent information, I have shared it with the Pontiac faithful around me. I have sent info to the P-P site about repairing mine. Many thanks!

[jehanHom]

This seems to be a really odd problem, if it were a bad connection higher than usual resistance in the signal path, the gauge would read lower that it should. Have you checked the system voltage to make sure it is correct? If the voltage regulator on the alternator was bad, that could lead to increased voltage and a higher than normal temp reading.