[ramairthreegto]

Be?

Waiting on my manuals in the mail.

Cruising along at 60, it looks like this.



That would seem a little cool to be accurate if 175 is supposed to be the center mark.

Right When it shut it off it goes right to the center marking.

When I start it up it goes all the way to 250 degrees than back down after I let off the start position on the ignition.

My 69 with a 400 and an aftermarket gauge instead of the idiot light runs about 160 with a perfectly mated propeller in the water pump and the fan should aligned air tight, about 180 to 190 after I changed the pump, without spending loving hours getting the absolute minimum prop clearance, and the fan shroud with a little more gap.

I am basically trying to dial in where to get worried on my gauge. I guess I cloud laser temp the in and out radiator hoses and get an idea.

[JamRSW6]

I had Pete Serio completely go through my speedometer, gauges and clock. Per his description on the temp gauge: Top line is 115, 1/4 line is 180, 1/2 line is 210, 3/4 line is 230 and the bottom line is 250. Jimmy

[JamRSW6]

Just noticed your oil pressure seems to be reading low for cruising at 60 mph?
Jimmy

[Peter Serio]

Post #1: "When I start it up it goes all the way to 250 degrees than back down after I let off the start position on the ignition."


This is a serious problem; on a rally gauge car the temperature gauge's dark green wire CANNOT run over to the ignition switch. Your ignition switch is grounding the green wire every time you turn the key to start your engine. The temperature gauge is most likely now damaged because of this. Banging the pointer up against the maximum overheat limit stop repeatedly is VERY HARD on the gauge!!!!! The other issuse is the silicone buffering fluid is probably long gone. These gauges all run off of 12 volts and they electromagnet that moves the pointer is pretty powerful for it's size. Inside where the disc magnet rotates is extra air space (GM put that into the design so that in extreme temperature conditions or operation in very dusty or humid conditions the gauge would never stick or bind.) Over the years this fluid will escape, once it does the pointer bangs up again the low limit stop every time you turn the key on (before you crank your starter.) Your gauges; both oil pressure and temperature should be tested; they probably need to be rebuilt.

[Forrest]

Originally Posted by Peter Serio

Post #1: "When I start it up it goes all the way to 250 degrees than back down after I let off the start position on the ignition."


This is a serious problem; on a rally gauge car the temperature gauge's dark green wire CANNOT run over to the ignition switch. Your ignition switch is grounding the green wire every time you turn the key to start your engine. The temperature gauge is most likely now damaged because of this. Banging the pointer up against the maximum overheat limit stop repeatedly is VERY HARD on the gauge!!!!! The other issuse is the silicone buffering fluid is probably long gone. These gauges all run off of 12 volts and they electromagnet that moves the pointer is pretty powerful for it's size. Inside where the disc magnet rotates is extra air space (GM put that into the design so that in extreme temperature conditions or operation in very dusty or humid conditions the gauge would never stick or bind.) Over the years this fluid will escape, once it does the pointer bangs up again the low limit stop every time you turn the key on (before you crank your starter.) Your gauges; both oil pressure and temperature should be tested; they probably need to be rebuilt.

Peter ..I'm confused about what you're saying.. I have 4 70's GTO's here and I have done dozens of the gauges with the car restorations.. When key is "off" water gauge tends to float downward,..oil just kinda stays somewhat..,When the key is turned to the "run" position both gauges oil and water go to the top..then when turned to the "start" (starter turns over) position the water goes to the bottom momentarily..once the car starts (key released from start) the water gauge is at the top until it warms up.. the oil immediately goes to the "correct" oil pressure..this is way they have always been..2 of the cars I have owned for at least 20+ years..and all the ones I have restored have done the same thing.. not sure if we're talking the same issue here?? Without going to schematics, I'm sure this is correct operation of these gauges..maybe do a poll on other owners of these cars?? All I can say is my cars are still working fine after 20+ years this way..and the many ones I have sold (that I keep in touch with!?) are also working as described..meant to say.. all the wiring I use in restorations is original harnesses and gauges that I have gone thru..never bought an "after market" harness or gauge pod

[ramairthreegto]

Originally Posted by JamRSW6

Just noticed your oil pressure seems to be reading low for cruising at 60 mph?
Jimmy

I was stopped and idling when I took the picture. Oil pressure comes up good with the rpms.

[ramairthreegto]

Originally Posted by JamRSW6

I had Pete Serio completely go through my speedometer, gauges and clock. Per his description on the temp gauge: Top line is 115, 1/4 line is 180, 1/2 line is 210, 3/4 line is 230 and the bottom line is 250. Jimmy

Thank you for that info. If that first line isn’t 180 then it seems just right.
I appreciate it.

[ramairthreegto]

I thought it was a built in function showing the gauge is good.

Now, I can’t say my gauges are perfect.

I was reading just between half a tank and 3/4 of a tank and it’s took 12 gallons.

Originally Posted by Peter Serio

Post #1: "When I start it up it goes all the way to 250 degrees than back down after I let off the start position on the ignition."


This is a serious problem; on a rally gauge car the temperature gauge's dark green wire CANNOT run over to the ignition switch. Your ignition switch is grounding the green wire every time you turn the key to start your engine. The temperature gauge is most likely now damaged because of this. Banging the pointer up against the maximum overheat limit stop repeatedly is VERY HARD on the gauge!!!!! The other issuse is the silicone buffering fluid is probably long gone. These gauges all run off of 12 volts and they electromagnet that moves the pointer is pretty powerful for it's size. Inside where the disc magnet rotates is extra air space (GM put that into the design so that in extreme temperature conditions or operation in very dusty or humid conditions the gauge would never stick or bind.) Over the years this fluid will escape, once it does the pointer bangs up again the low limit stop every time you turn the key on (before you crank your starter.) Your gauges; both oil pressure and temperature should be tested; they probably need to be rebuilt.

[Forrest]

great! glad I could help... good luck with your build

[Peter Serio]

In reply to Post #5.

Peter ..I'm confused about what you're saying.. I have 4 70's GTO's here and I have done dozens of the gauges with the car restorations.. When key is "off" water gauge tends to float downward,..oil just kinda stays somewhat..,When the key is turned to the "run" position both gauges oil and water go to the top..then when turned to the "start" (starter turns over) position the water goes to the bottom momentarily..once the car starts (key released from start) the water gauge is at the top until it warms up..


All I can say is that on a GM car with a temperature gauge it is very hard on the gauge to ground the dark green wire. This takes the gauge from cold Ohms; say right around 575 or 600 to .5 or zero resistance. Which bangs the edge of the aluminum pointer up against your high limit stop. There is no condition of engine temperature which would cause the resistance of a sender in a gauge car to ever go to zero!!! To put it in context the maximum overheat line on a 1970 GTO temperature gauge is 250 degrees. The sender is giving ohms resistance of 51 ohms to obtain a 250 reading on the dial. That said, all GM cars made with red warning lights in the dash instead of gauges are wired to ground the green wire (thru the ignition switch) every time you crank the starter. The cars were wired this way to give the driver a "bulb test." I think because the cars are similar enough in wiring Pontiac division allowed that fork in the green wire (over to the ignition switch plug) to remain, but to me it's a bad idea. Previous year GTOs with rally gauges do NOT ground the green wire upon cranking. When the cars are old and the buffering fluid inside of the air space within the center of the each gauge becomes exhausted banging the edge of the temperature gauge pointer (aluminum) up against the high limit stop (steel) every time you crank the starter leads directly to gauge failure. I have personally rebuilt more than 100 (both oil and temperature gauges) due to this failure mode.

When the ignition switch is turned off GM cars with gauges, oil pressure, fuel level and coolant temperature can come to rest at any place on the dial, it does not mean anything. They simply come to a stop or sometimes migrate where they want to. It is only when you go to re-start the car; and apply 12+ volts to the coil(s) via the key switch that the gauges respond.

[Forrest]

...yes.. temp gauge bottoming when "starting"..is normal...my schematics from 70 -72 all show the "fork" off the gauge plug with the one dark green wire going to ign. switch..don't know about previous years...I guess I'll just remove that darn green wire from the ign. sw. from now on!..maybe I have just been fortunate that all the water temp gauges still work perfectly..although I must admit, I have used a small resistor in series from sender (hidden) to "sometimes correct" the gauge!..worked fine..