[berrygoat]

Guys,, here is the deal
77 TA, factory Temp Guage
It now moves from an 1/8th of an inch from the left to 100 then stops
In 2004 bought car, didn't work
In 2006 new 455, new Napa sender and it read 260 (It wasnt really hot)
Then it stoped working
June 2012 chANGED sender to one from Lectrid Limited, read about 200, perfect
Now, wont move off of 100 degrees
Got new sender from Lectric Limited, still at 100
11.8 volts at wire with key on
14 volts at wire with car running
Sender is well ground
It is stuck at the 100 portion of the dial. Any thoughts ? Thanks

[rexs73gto]

Where are you mounting the sender to read the temp???? Are you getting a sender & not a switch??? A sender is for a guage & a switch is for a light. Next have you checked the coninuity to & from the gauge in the dash. Have you made sure the wire your connecting to the sender is the proper color wire? Did you use tefleon tape on the threads of the sender??? If you did take it off, not sealer of any kind on the threads should be used as that will make the sender act funny. Are you useing a connector or bear wire to connect the sender????? When you changed the enginge have you went through the wire harness to make sure the wire is not pinched somwhere??? Did you take the wire harness out of the car when you swapped engines, make sure the harness is plugged back in to the bulkhead connector nice & tight & the center screw screwed back in tight, with fresh dielectirc grease in it????

[berrygoat]

It's the correct wire going to the factory location in left side head. No teflon tape, as I stated the sender is ground. It is the correct sender. I did change the engine harness to a new unit from M&H when I changed the engine. The wire to the sender has power as mentioned.

[Old Goat 67]

Sounds like your gauge is toast.

Need to prove it one way or the other to pinpoint it.

Substitute resistance on the sense lead with known value resistors to ground.

I am not good enough on that year to tell you what those would be, but for my 67 they are as such.

Place a 90 ohm resistor from the end of that to a good ground, gauge should read 1/2 scale -a bit maybe 1/16" to 1/8". A 45 ohm should cause the gauge to read full scale "hot."

If you unplug the green wire from the sender the gauge should read 100, (cold). If you connect the unplugged engine compartment end of your green wire to a 90 ohm resistor and then the other end of the resistor to engine block ground the gauge should read just to the right of 1/2 scale. In some cases it is actually a bit closer to the 3/4 scale mark. If you connect the green wire to a 45 ohm resistor then the other end of the resistor to ground the gauge should read all the way right (full scale-245 degrees)-{overheat}. The least resistance any temperature sender would give is around 45 to 44 ohms, this is why YOU SHOULD NEVER GROUND ANY 45 year old dash gauge, as it "jambs" it up against it's internal limit stop, if the gauge is on it's last leg anyway, this could kill it.

Maybe Peter Serio on here can give you exact values.

Charles

[berrygoat]

When I ground the lead off the harness the guage pegs to the right like it should.

[Old Goat 67]

Hmmmm, don't hold that long, just touch to see movement.

Which harness? Dash or engine?

Can you have an open from back of gauge to sender?
That should measure 0 ohms.

[berrygoat]

The lead for the sending unit is on the engine harness

I would have to pull the guage to get to the back, im trying to avoid that

[Old Goat 67]

Well, that sounds like you have proved the gauge and the lead to the sending unit to be OK, but if the sending unit has been changed. Sumtin's not right here.

Does the sending unit measure resistance across it or is it reading open?

They should read varying resistance as they heat up, that's what makes the gauge vary.

Can you read the resistance with an ohm meter?

Maybe you got the wrong sender? Just guessing.

If you could run down to Radio Shack and get a couple of resistors to put in place of the sender, we could nail it down for sure. A 90 ohm and a 45 ohm should give you half scale and full scale respectively, IF in fact it would be the same as a 60's sender.

[Old Goat 67]

Hey, what's the part # on the new sender you got from Lectric Limited?

[berrygoat]

Originally Posted by Old Goat 67

Hey, what's the part # on the new sender you got from Lectric Limited?

01513321 This is the second one. They replaced the first one thinking it maybe defective.

[Old Goat 67]

Looks to be correct. What the hey?

Better resort to measuring it's resistance at various temp's and/or substituting it with some resistors.

[berrygoat]

Could it still be the guage ?

[Old Goat 67]

Could, but you'll be guessing till you prove it first!

[Peter Serio]

The sending unit(s) for all coolant temperature gauges have no moving parts inside of them. Therefore, there is nothing to "wear out" or go bad. In 25 years of working on cars I have seen only 2 or 3 of them that were actually "bad." As I recall 2 of those were from external heat (engine fire) that partially melted the black plastic insulator on top. Now matching (calibrating) the sender to a dash gauge in a specific year, make and model car, THAT is a WHOLE different story!!!! I have personally tested dozens of different aftermarket and replacement senders alongside of the original AC 12 Volt, made in U.S.A. senders (side-by-side) in boiling water.

It is unbelievable the amount of variance (at normal operating engine temperature) i.e. 185 to 197 degrees; I am seeing in aftermarket parts vs. the original GM sender(s).

(The NAPA #TS6 is one of the very WORST!! That sender constantly causes the dash gauge to display a reading in excess of 25 degrees higher than actual coolant temperature!!!)


As to the trans am gauge, it sounds like it is "sticking" or something is binding up the pointer. (Preventing full warm-up on the dash dial.) This issue is not common to those gauges but it can happen. I would say your next step is to remove the dash cluster and examine both the gauge and the printed circuit. This also could be a wiring problem, either dash or engine compartment.

[berrygoat]

Originally Posted by Peter Serio

The sending unit(s) for all coolant temperature gauges have no moving parts inside of them. Therefore, there is nothing to "wear out" or go bad. In 25 years of working on cars I have seen only 2 or 3 of them that were actually "bad." As I recall 2 of those were from external heat (engine fire) that partially melted the black plastic insulator on top. Now matching (calibrating) the sender to a dash gauge in a specific year, make and model car, THAT is a WHOLE different story!!!! I have personally tested dozens of different aftermarket and replacement senders alongside of the original AC 12 Volt, made in U.S.A. senders (side-by-side) in boiling water.

It is unbelievable the amount of variance (at normal operating engine temperature) i.e. 185 to 197 degrees; I am seeing in aftermarket parts vs. the original GM sender(s).

(The NAPA #TS6 is one of the very WORST!! That sender constantly causes the dash gauge to display a reading in excess of 25 degrees higher than actual coolant temperature!!!)


As to the trans am gauge, it sounds like it is "sticking" or something is binding up the pointer. (Preventing full warm-up on the dash dial.) This issue is not common to those gauges but it can happen. I would say your next step is to remove the dash cluster and examine both the gauge and the printed circuit. This also could be a wiring problem, either dash or engine compartment.

Thanks, I replaced the printed circuit last year. I thougt I could rule out wiring as I have juice in wire running to the sender, am I wrong on that ?

[Peter Serio]

Live voltage in the dark green wire on top of the sender is a good sign. I would say you need to go to radio shack (or, on-line) and get some fixed ohm 1 or 2 watt resistors. The "old school test" way of full sweeping a temperature gauge (which I DO NOT RECOMMEND) is to remove the green wire from the gauge, turn the key to the on or run position (but do not start your engine) and for a split-second touch the end of the green wire to ground. This should cause the pointer to go from 100 (cold) degrees all the way over to maximum overheat.

The problem with this test is that if a gauge is on it's last leg and about to fail this "test" could easily to be the nail in the coffin!!

"Overheat" on a GM temperature gauge is from between 45 and 53 ohms.

[berrygoat]

Originally Posted by Peter Serio

Live voltage in the dark green wire on top of the sender is a good sign. I would say you need to go to radio shack (or, on-line) and get some fixed ohm 1 or 2 watt resistors. The "old school test" way of full sweeping a temperature gauge (which I DO NOT RECOMMEND) is to remove the green wire from the gauge, turn the key to the on or run position (but do not start your engine) and for a split-second touch the end of the green wire to ground. This should cause the pointer to go from 100 (cold) degrees all the way over to maximum overheat.

The problem with this test is that if a gauge is on it's last leg and about to fail this "test" could easily to be the nail in the coffin!!

"Overheat" on a GM temperature gauge is from between 45 and 53 ohms.

I did that test and it swept all the way to the right as it should.

[Old Goat 67]

Ah ha, the guru found you!

[berrygoat]

I have a multi-meter, should I test something ? Im thinking bench testing the sending unit I just took out but how do I do it ?

[Ben M.]

Originally Posted by Peter Serio

(The NAPA #TS6 is one of the very WORST!! That sender constantly causes the dash gauge to display a reading in excess of 25 degrees higher than actual coolant temperature!!!)

I concur with this. I've got a sending unit from NAPA that reads 210. The mechanical gauge read 185 in the same spot. It's annoying, but not enough to change it just yet. Who do you recommend for a gauge sender these days? Obviously OEM GM is preferred but that's not an option here now unfortunately.

As to the problem at hand, have you taken any measurements at all on the sending unit? Put it in boiling water or back in the car and measure the resistance from the button to chassis ground. The values given previously in the thread are what you should be looking for.