SECOND GEN WATER TEMP GAUGE INACCURATE - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

79ZRAG · 05-30-2009, 07:46 AM

I'm at a total loss here and could really use somehelp !!

Just wondering if any of you second gen owners have had this problem. This is the problem that I'm having with my 1979 Z/28.

My OEM water temp gauge reads 240, but the actual temp is 180. This is what I have done to date. NEW OER gauge, new OER engine wiring harness, new Carquest temperature sending unit (bought two just to be sure), new OER shunt resistor on back of the gauge, new OER circuit board (back of cluster).

I have tried three other used OEM gauges and they read EXACTLY the same as the new OER gauge, but when I connect an aftermarket temp gauge directly to the sending unit, it reads exactly 180 degrees (which is the actual temerature).

After hours of research, I strongly suspect that the, sending unit resistance must be slightly different than the the OEM one was (GM has discontinued the sending unit). I have been experimenting with changing the resistance of the shunt resistor in back of the gauge, and tried a resistor in line with the sending unit wire. Yesterday, I put a 30 OHM resistor in line with the sending unit wire and was able to bring the gauge down to 190, but I wish I could correct the problem without adding resistors.

If anybody out there knows anything about this, I could sure use some advise. Thanks, Ken, Bastrop, Texas.

zman302 · 05-30-2009, 08:03 AM

Are you sure carquest has sold you the right unit, what is the part number they have giving you?

79ZRAG · 05-30-2009, 08:12 AM

I don't have the box anymore, but Carquest was the only local parts store that even showed the correct application for my vehicle. O'Reilys told me that it was not available and Advance sold me one that had a smaller thread size (had to buy an adapter to make it fit the block), it provided the same reading as the Carquest sending unit.

I saw a sending unit in either Classic Industries or NPD, that i'm thinking about trying, but they are asking a small fortune for it. I'm afraid that I will buy it with the same results.

zekefreak · 05-30-2009, 08:22 AM

That's a strange one for sure. I've never heard of that. Does OER have a tech support #? Maybe give that a try. Try www.nastyz28.com and ask them, I'm sure someone on that board will have an answer for you.

zman302 · 05-30-2009, 08:30 AM

According to AC delco, there are two units for 79, Part #213-79 which is a collar button style, Carquest number ts-71. The other is a 1 blade style, part number d1878 and the carquest number for it is ts32. Check to see what style is correct for 79, you might check with your local dealer as these delco numbers are good numbers and still availible. I work for a parts company that also sells delco to the dealers, our price is 34.79 for the 213-79 and 13.63 for the d1878 so the dealer shouldn't be too far off that, sometimes they sell them cheaper than we do because of different markup rates

79ZRAG · 05-30-2009, 08:41 AM

ZMAN302 - Thanks for the info, I will follow up on those part numbers, mine is the single blade sending unit. Ken

zman302 · 05-30-2009, 08:54 AM

I hope they help, everytime i have had problem like yours its been the sending unit, aftermarket ones never seem to have the correct ohms readings and cause inaccurate readings

79ZRAG · 05-30-2009, 09:22 AM

I'm going to continue with this today. I'll let you know. Ken

Stingr69 · 05-30-2009, 10:26 AM

The idiot light has a different sender. You probably know that already.

You can calibrate it fairly close with a resistor. Not perfect but it will work better. A rheostat in paralell can be used to trim the sender resistance. When you get the reading just right, you can take it off and measure the resistance with an ohm meter and purchase a resistor from radio shack to do the job of the rheostat.

OR, you could just pull the needle off and reposition it.

Not perfect, just close.

-Mark.

79ZRAG · 05-30-2009, 05:13 PM

"You can calibrate it fairly close with a resistor. Not perfect but it will work better. A rheostat in paralell can be used to trim the sender resistance. When you get the reading just right, you can take it off and measure the resistance with an ohm meter and purchase a resistor from radio shack to do the job of the rheostat".

I bought a 0-25 ohm rheostat from Radio shack yesterday, and put it in series with the sender. Maxed out at 25 ohms I was able to get it down to 200, a 30 ohm 1/4 watt fixed resistor brought it down to 190. I'm guessing 35-40 ohms should get it around 180 (where it should be). I'm going to have to see the local Chevy dealer to find the AC Delco sender that was mentioned earlier, perhaps then I can eliminate the resistor. Thanks

05-30-2009, 07:46 AM	#1
79ZRAG Drives: 1979 Z/28 NCE LIMITED EDITION Join Date: May 2009 Location: Bend, Oregon Posts: 26	SECOND GEN WATER TEMP GAUGE INACCURATE I'm at a total loss here and could really use somehelp !! Just wondering if any of you second gen owners have had this problem. This is the problem that I'm having with my 1979 Z/28. My OEM water temp gauge reads 240, but the actual temp is 180. This is what I have done to date. NEW OER gauge, new OER engine wiring harness, new Carquest temperature sending unit (bought two just to be sure), new OER shunt resistor on back of the gauge, new OER circuit board (back of cluster). I have tried three other used OEM gauges and they read EXACTLY the same as the new OER gauge, but when I connect an aftermarket temp gauge directly to the sending unit, it reads exactly 180 degrees (which is the actual temerature). After hours of research, I strongly suspect that the, sending unit resistance must be slightly different than the the OEM one was (GM has discontinued the sending unit). I have been experimenting with changing the resistance of the shunt resistor in back of the gauge, and tried a resistor in line with the sending unit wire. Yesterday, I put a 30 OHM resistor in line with the sending unit wire and was able to bring the gauge down to 190, but I wish I could correct the problem without adding resistors. If anybody out there knows anything about this, I could sure use some advise. Thanks, Ken, Bastrop, Texas. __________________ "THE GREAT MASS OF PEOPLE WILL MOST EASILY FALL VICTIM TO A BIG LIE THAN TO A SMALLL ONE"

05-30-2009, 08:12 AM	#3
79ZRAG Drives: 1979 Z/28 NCE LIMITED EDITION Join Date: May 2009 Location: Bend, Oregon Posts: 26	I don't have the box anymore, but Carquest was the only local parts store that even showed the correct application for my vehicle. O'Reilys told me that it was not available and Advance sold me one that had a smaller thread size (had to buy an adapter to make it fit the block), it provided the same reading as the Carquest sending unit. I saw a sending unit in either Classic Industries or NPD, that i'm thinking about trying, but they are asking a small fortune for it. I'm afraid that I will buy it with the same results. __________________ "THE GREAT MASS OF PEOPLE WILL MOST EASILY FALL VICTIM TO A BIG LIE THAN TO A SMALLL ONE"

05-30-2009, 08:41 AM	#6
79ZRAG Drives: 1979 Z/28 NCE LIMITED EDITION Join Date: May 2009 Location: Bend, Oregon Posts: 26	ZMAN302 - Thanks for the info, I will follow up on those part numbers, mine is the single blade sending unit. Ken __________________ "THE GREAT MASS OF PEOPLE WILL MOST EASILY FALL VICTIM TO A BIG LIE THAN TO A SMALLL ONE"

05-30-2009, 09:22 AM	#8
79ZRAG Drives: 1979 Z/28 NCE LIMITED EDITION Join Date: May 2009 Location: Bend, Oregon Posts: 26	I'm going to continue with this today. I'll let you know. Ken __________________ "THE GREAT MASS OF PEOPLE WILL MOST EASILY FALL VICTIM TO A BIG LIE THAN TO A SMALLL ONE"

05-30-2009, 05:13 PM	#10
79ZRAG Drives: 1979 Z/28 NCE LIMITED EDITION Join Date: May 2009 Location: Bend, Oregon Posts: 26	"You can calibrate it fairly close with a resistor. Not perfect but it will work better. A rheostat in paralell can be used to trim the sender resistance. When you get the reading just right, you can take it off and measure the resistance with an ohm meter and purchase a resistor from radio shack to do the job of the rheostat". I bought a 0-25 ohm rheostat from Radio shack yesterday, and put it in series with the sender. Maxed out at 25 ohms I was able to get it down to 200, a 30 ohm 1/4 watt fixed resistor brought it down to 190. I'm guessing 35-40 ohms should get it around 180 (where it should be). I'm going to have to see the local Chevy dealer to find the AC Delco sender that was mentioned earlier, perhaps then I can eliminate the resistor. Thanks __________________ "THE GREAT MASS OF PEOPLE WILL MOST EASILY FALL VICTIM TO A BIG LIE THAN TO A SMALLL ONE"

05-30-2009, 08:03 AM	#2
zman302 DZ 302 4spd Drives: 1969 Z/28 Join Date: Sep 2006 Location: Ohio Posts: 131 View My Garage	Are you sure carquest has sold you the right unit, what is the part number they have giving you?

05-30-2009, 08:22 AM	#4
zekefreak Sweet Sassy m' lassie Drives: 1979 Z28, 2010 SS/RS Join Date: Mar 2009 Location: Baden, PA Posts: 112	That's a strange one for sure. I've never heard of that. Does OER have a tech support #? Maybe give that a try. Try www.nastyz28.com and ask them, I'm sure someone on that board will have an answer for you.

05-30-2009, 08:30 AM	#5
zman302 DZ 302 4spd Drives: 1969 Z/28 Join Date: Sep 2006 Location: Ohio Posts: 131 View My Garage	According to AC delco, there are two units for 79, Part #213-79 which is a collar button style, Carquest number ts-71. The other is a 1 blade style, part number d1878 and the carquest number for it is ts32. Check to see what style is correct for 79, you might check with your local dealer as these delco numbers are good numbers and still availible. I work for a parts company that also sells delco to the dealers, our price is 34.79 for the 213-79 and 13.63 for the d1878 so the dealer shouldn't be too far off that, sometimes they sell them cheaper than we do because of different markup rates

05-30-2009, 08:54 AM	#7
zman302 DZ 302 4spd Drives: 1969 Z/28 Join Date: Sep 2006 Location: Ohio Posts: 131 View My Garage	I hope they help, everytime i have had problem like yours its been the sending unit, aftermarket ones never seem to have the correct ohms readings and cause inaccurate readings

05-30-2009, 10:26 AM	#9
Stingr69 '69 Owned Since '79 Drives: '69 Z/28 LeMans Blue w/White Join Date: Oct 2008 Location: LR AR Posts: 1,847 View My Garage	The idiot light has a different sender. You probably know that already. You can calibrate it fairly close with a resistor. Not perfect but it will work better. A rheostat in paralell can be used to trim the sender resistance. When you get the reading just right, you can take it off and measure the resistance with an ohm meter and purchase a resistor from radio shack to do the job of the rheostat. OR, you could just pull the needle off and reposition it. Not perfect, just close. -Mark.

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