66 gauge repair

[66GTOLVR]

My rally temp gauge is not working correctly. Is there anyone local that I can send or take the pod to for testing, repair, and calibration to the sender? Replaced with new sender from Lectric Limited with no good results. Was told the coils inside are probably bad.

Guidance is appreciated.

[Lfowler]

Hi Larry, I just went through this with my 1965 convertable. My instrument read full scale all the time. The oil pressure and water temp gauges are identical electrically. They can be temporarly swapped to check the "bad coil" theory. I found an open ground at the gauge cluster to be a lot of my problem and a hair wisker of coil winding wire that sometimes touched where it should not go. It took a magnifiing glass to see it. There are several old posts of the progress and false starts on this posting board. There was a missing tab on my temp gauge that made the circuit complete. I don't know how long it was gone or if it had never been installed and the gauge found a false ground until the car got old and needed all the returns. Mine sat a long time at variouos points, and got wet inside, which really stressed the electrics. Good luck. I could test the gauge for you if you wanted to send it down by itself. Ladd.

[66GTOLVR]

I hate electrical problems. So changing the wiring on the gauges does what? One senses temp the other pressure. How would that work for a test or what would i look for when switching the wires and starting the car?

[Lfowler]

Ah, I see where your coming from. I believe your thinking of switching the sender wires under the hood. I refered to switching the gauges in cluster. That way the oil pressure gauge would be reading the temp sender via the engine wiring harness. It would read low or no "pressure" when the engine started and gradually would rise to mid scale as the engine warmed up in 5 or ten minutes time.

The temp gauge would be reading the oil pressure sender. It should be at low scale when the key was turned on and immediately jump up to mid / high scale when the engine fired off. If the pattern of failure followed the gauge then replace the gauge. If it stayed with the position of the gauge in the cluster then the problem is in the sender or wiring loom.

Switching the leads under the hood should produce similar logic but the oil sender wire has a different type of plug than the temp sender so a jumper would be needed. Under the dash the oil and temp gauges have "keyed" push on connectors which prevent incorrectly plugging them in. However those connectors are just screwed onto the gauge back and can be temporarly swapped to allow the test.

Both gauges function in identical ways reading voltage controled by resistance in the sender. The oil pressure sender converts pressure to a changing resistance value porportional to the pressure applied to it. The tempurature sender converts tempurature (heat) to a changing restance valve porportional to the heat applied to it. The only difference is one gauge says oil pressure and reads needle down and the other says temp and reads needle up because the lettering goes that way.

I guess it depends on if you have the dash cluster out or not which is easier. I did the gauge swap because I'd already swapped senders, had a replacement gauge to try, and was replacing the interior / painting the dash anyway.

This is a very cool web site but I don't know how to find the spell check. Sorry for some goofs.
Regards, Ladd

[66GTOLVR]

Ladd, I am going under the dash in a few days to swap the wires on the gauge pod under the dash. Hopefully i can get in there and unplug them both and switch them around. Will let you know what happens.

[HOTROD64-STOCK69]

HOLD ON THERE TRIGGER...
The EASIEST way to test the gauge functions is
1. With both sending units unplugged under the hood, turn the key to 'run' set your voltmeter to DC and ground the negative lead. Find a positive source and verify DC voltage. With that done tag one of the wires on the back of the gauges. It will read the same voltage as when you tested your meter. If it reads less, then test the other connector on the same gauge. If you have voltage there, ground the sending unit for each gauge. If the gauge pegs then the sending unit is good. If the gauge does nothing then the gauge is bad. FYI: The temp and oil switches are what is known as 'normally open' meaning the switch will close toward ground when heat or oil pressure are present. So if you ground the sending unit wires the gauges should read 100% respectively. Mike

[66GTOLVR]

Mike, Ladd: Thank you both for your input. I am terrible with electrical thus all the ? about this. Here is what i did since you both posted tests.

Since I cannot really use a voltmeter very well this is what i did. I disconnected the temp sender wire at the sender - grounded the wire to the battery negative post - turned key on and had my son touch and untouch negative battery post while i watched temp gauge needle - with key on and not grounding gauge needle was all the way left (100/COLD) - once grounding to battery post the needle went/pegged to the right(245/HOT) - touched on and off a few times and that was the same all the time.

Ladd, I tried your version of tests and switched the wires under the hood since the gauge is still in the car. O/P gauge did nothing as far as moving like a temp gauge. Barely if anything after car ran 15 minutes. Temp gauge moved to the 215 area mark when reving the engine past 3K. Not any farther like the op gauge needle does. Switched all back and the temp gauge read 215 or a little higher area.

According to Mike's theory all is well in my system if i read his post correctly. Of course i did not check voltage to the gauges (Will need help with that). The temp gauge rises slowly when driving then hits a point a little past 180 mark and pegs/moves quickly to the right. Then it moves back to 215 area and back to 245. Does not work right in my opinion at least not the same as my last 66.

I am really baffled with this. I have been told my gauge needs repaired and that the coils inside need replaced. It looks like a pain to get the gauge out. (Bad Back) So i want to make sure before i go through the pulling of the gauge.

Thank you all for your help.

[Lfowler]

Hi fellows, Certainly a volt meter is a great tool to trouble shoot with. I use them all the time. But, like you I have a bad back and crawling under the dash is a thing I did far easier when I was younger, and when I didn't wear progressive bifocals that screw up seeing anything well. By the time I get under there, wedge my shoulder between the shifter and console, hang my feet over the seat, position my head so I can see the test probe there isn't much left in me to read the LED display of a meter: If the trouble light hasen't washed out the contrast so bad I couldn't see it even if I could focus on it.

That is why I think sometimes a guy gets a lot of bang for the buck by pulling the cluster out. Changing all the bulbs, speedo cable greese job, checking if the ignition switch plug has melted yet, etc. And you can get the cluster up on a workbench where electrical testing is more certain and easier. Then when your done, your done for many years with that part of the car and that is important to me.

But that said, I wonder if the car is having trouble or the gauge is. A temp spike could be air in the cooling system or a sticking thermostate. Have you tried disconnecting the temp. sender and putting a different sender of the correct application in the circut and testing for heat rise indenpendant from the engine as a source? Hold it in the air by a pair of vice grips (gently) and ground the vice grips with a jumper wire. Turn the key on then wave a lighter on the sender and watch the gauge. It will rise pretty quickly as it gets hot and fall off more slowly as it cools. With long jumpers this can be done sitting in the drivers seat alone. Gauge motion should be smooth and progressive.

There are several types of electrical automotive temp. senders. Switch types are on or off, or rather open or closed electrically. They are used in cars with warning lights. Variable restisance senders are comonly used with gauges as I believe we have here. Pluse type senders are also used that open and close to drive heater elements which drive bimetalic spring gauge mechinisms are also out there but not in your Pontiac of mid sixtys vintage.

Because the gauge your dealing with is magneticly driven by a coil it can be fooled into moving by waving a permanant magnet close to it and dragging the pointer across the scale carefully. This will check for binding of the pointer pivot or if the needle is rubbing on the scale causing a bind. Don't worry about the gauge not returing to rest as it once did after doing this. Once a proper current is applied to the coil it will readjust the magnetic field driving the pointer, and the gauge will return to "normal".

If the coil is burnt out it will be open and do nothing to move the gauge. If the coil is shorted it will pass too much current and overdrive the gauge because of an overstrong magnetic field being produced. (Quick movement and pegged pointer) The gauge may or may not finish burning out and quit working thereafter.

There are lots of ways to figure this out. I guess the best way is the one you can do and the one that finally does the job. Good luck, Ladd.

[66GTOLVR]

Here are the volt meter tests from under the dash. With these readings what you do think about the temp gauge?

Temp gauge wire readings: Pink wire 12.25 VDC - Green wire 12.24 VDC

Oil Pressure wire readings: Pink wire 12.23 VDC - Blue wire 8.38 VDC

Tested tach brown wire for volts under dash: 12.28 VDC

Battery Voltage: 12.56

As posted earlier the temp gauge needle pegs to the right when grounding the wire from sender to battery ground. When running car temp goes to approximately 180 then moves quickly to right (245) then goes back to 215 and back and forth.

Coolant full, gauge works same with 2 different senders. (1 AC Delco-button top, 1 Lectric Limited-spade top)

Comments? Pull gauge and send out for repair? That is where i am at?

Thanks for the input.

[66GTOLVR]

Gauge was taken out of the car and sent into THE TACHMAN for testing and repair. $100 to test, replace / rewire coils in gauge and calibrate with his calibration machine. Gauge tested bad.

So all the headaches of questions etc are over. Just need to wait for gauge to be returned and installed. Then hopefully all works well.

Thanks for all the input.

[Lfowler]

That sounds like good news about your gauge being bad. I thought the voltages looked about right but didn't comment as I hadn't made the measurements and didn't know who's meter you used (digital or analog) or how you grounded the meter. (That and I've been really busy on a project and off the forum for a couple of days.) If on an analog I'd have expected the battery supply voltages to the vehicle gauges to be exactly the same. Digital meters will float and show finer variations sometimes.

I'd be real interested in how this gauge repair turns out. I think I saved my old gauge thinking to have it rewound someday if the cost wasn't excessive. I remember it was sorta hard to find them and I nearly had to buy a complete used cluster to get one. My old gauge has a broken coil winding wire that contacts the case intermittantly and causes full scale movement to occure. Then it arced and stuck causing the gauge to peg all the time power was applied. When I would fool around testing it would sometime come loose, work a bit, then fail. I also had insufficent grounds to the cluster which made the readings out of calibration. Ladd

[66GTOLVR]

Will keep you posted on how it turns out.

[HOTROD64-STOCK69]

The blue and green wires are the ones that come from the senders, so voltage there is pass thru from the supply (red) wire. It sounds like you have nailed it. Good luck, ah projects, yes yes Mike

[66GTOLVR]

Just received email from Gary in South Carolina that the gauge is on its way back via UPS. Recoiled, oil pressure gauge tested (FINE), lens polished and inside cleaned up.

Hopefully this weekend I will be under the dash installing the gauge. Lets hope so. I want to go for a ride and play since the weather is finally cooperating.

More to come.

[G6T8O]

Congrats....And GOODLUCK!!!!

[Lfowler]

That was fast. Sounds like good service so far. Ladd

[66GTOLVR]

Received my gauge back today from the repair shop. Now the fun starts of re-installing. Tested working condition now according to his paperwork. Will try to install this weekend and let you know how it works. HOPEFULLY THIS WEEKEND with all these other projects to do since it is so SUMMER LIKE.

[THUNDERGOAT]

Hey Larry bring the white tiger out to the Rainier run on saturday. Its going to be a blast. cars leave Orting between 9a and 11a.

hope to see you there

Paul

[66GTOLVR]

Goat leaks oil bad to run that far. Otherwise I would be there. Once I can afford the engine rebuild i will be there.

[66GTOLVR]

Temp Gauge POD installed tonight. Test run for a while and gauge seems to be working correctly. 1 time it suddenly jumped to 245 then back to normal 200-210 range. That was the only time it didn't seem to act correctly.

Maybe it was getting use to its new windings etc...????

Will fire up again another day later this week to test the operation of the temp gauge and go for a GAS ride to fill up. OUCH!!!!!! But oh what fun when they look at you go by.

Back on track of the gauge. So far so good. Thanks to all that input repair suggestions to help me out. This is a great club to belong to and a heck of a web site for help.

Will let you know on the next ride if gauge seems to work well.

Still need to reinstall radio, ashtray etc but car is driveable.

HEY AL WHERE IS THE PHOTO OF THE RADIO BRACKET???
Find an extra one yet???

[66GTOLVR]

Took goat out for another test ride before installing radio, etc... The temp gauge acted the same as above again. Warmed up to 180 then after a period jumped again to 245 then went back down to the 180 area.

Seems like that happens during the initial engine warm up. Keep driving car and no other fluctuations after the initial jump that I have noticed.

Possible sticking t-stat, incorrect sender? Have an AC Delco sender i will install to see if that makes any difference. Presently have a Lectric Limited sender in car now.

If no change I will get new t-stat. Had new t-stat installed 3 years ago and not driven much. Could it be bad/sticking already?

Comments??

[Lfowler]

Hi fellows, I'd go with your guess and remove the thermostat. Then retest drive the car.

There is a lot to be said about (lack of) quality in modern thermostats and deviation in design from original specification in subtle details. Notably the rate of opening is faster once operation temperature is reached while the point of opening is more closely defined. I suspect the material used to activate the valve in a thermostat has been changed to allow tighter sealing during warm up then faster cycling to achieve more stable engine temperature so modern injection systems don’t have to chase the mixture so much. The down side of this is air trapped in the cooling system doesn’t bleed out past a thermostat valve during engine warm up as it once did. The trapped air insulates the temperature sensing portion of the thermostatic valve causing late opening and localized engine overheating. Many manufacturers have posted service bulletins regarding bleeding air out of modern cooling systems and denied engine failure warranty claims because tech’s haven’t been able to prove they bleed the cooling system properly.

Sometimes this problem is seen on a dashboard temperature gauge as a spike during warm up because the sender is in a different physical location on the engine than the thermostat. Sometimes not. When heat conducted to the thermostat via steam or metallic paths get it hot enough it finally opens, releases the trapped air, cools the engine and works fine until air, for whatever reason, is trapped behind it again.
For older car owners using “modern” parts this means conversion to a truly sealed cooling system with a coolant recovery tank or modification to thermostats to allow a bleeding action is needed to let trapped air migrate to the upper radiator tank area and/or out of the system entirely. It also means figuring out if the quantity of air trapped behind the thermostat is “normal” or excessive. If it is normal then drilling a 3/16th hole in the thermostat outer ring area and installing it “up” or “forward” in relation to flow will cure the spike. Some brands of thermostat already have a hole for some modern applications and some have a hole with a small cotter key that rattles around promoting flow by breaking up surface tension of trapped bubbles. However the applications which need a hole and those which get one don't match up too well even on the new cars to say nothing about older vehicle applications consoldated into modern part numbers. Installing a recovery tank and sealed system plumbing will minimize trapped air and give other benefits. If the amount of trapped air is abnormal then that problem has to be figured out as well, fixed, then the other solutions implemented.

I have personally seen head temperatures of 500+ degrees while the water temperature indication was less than 150 when a thermostat had air trapped behind it on a small block Chevy. The physical construction of the engine was compromised and later failed. Head temperature spikes to 400 degrees can be common with this problem with attendant valve guide wear, oil consumption, and warping or blown head gaskets over time. Any “V” series engine or engine where the thermostat is high on the cooling system assembly in relation to the water pump bypass hole is prone to have this happen.

Again, Best of luck to you. Ladd

[66GTOLVR]

thanks Ladd. Will look at my t-stat and see if there is a hole. if not will drill one to the size you suggested. Then go for another ride. Man i hate those rides. LOL

[Lfowler]

Ya I know. Sometimes it can take all day. Ladd

[HOTROD64-STOCK69]

Do yourself a favor and buy a 160 thermostat drill a 1/8 or 3/16 hole in it and be done with it. Jeez, if your gonna open it you might as well change it out since it acts like its 'slow' yes I said 160! Mike

[66GTOLVR]

Gauge all installed and it works great. I needed to burp the system after changing the heater core. OOOOPS forgot to do that at the end of changing the core. Since burping the gauge works fine.

Thanks to all that had input. You all are great and helpful.