Sporadic Temperature Gauge - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**DANTIP** · 10-23-2018, 01:36 PM

The temp gauge in my '72 works sporadically and I'm hoping to get some guidance. It reads correctly about 1/2 the time and can change wildly. Sometimes it will be pegged when cold. When driving it can change very quickly and obviously not correctly. Thoughts??

**Steeveedee** · 10-23-2018, 02:59 PM

Check the wire from the transducer, the gauge and the printed circuit. In my case, I couldn't be bothered and just put in a mechanical gauge that I already had on hand.

**truckster** · 10-23-2018, 03:03 PM

It's most likely a wiring issue. The sending unit either works or it doesn't; it's rare that they'll work sporadically. What's most likely is that there is either a break or a short in the wire to the sending unit.

sick472 · 10-23-2018, 03:12 PM

A short anywhere in the circuit can cause the jumping around you are seeing. Hopefully it is a wire that can be fixed/tightened/taped, otherwise it may be the sending unit itself that needs changed out or the circuit board that Stevee mentioned.

**LockDoc** · 10-23-2018, 05:39 PM

-
If any thread tape or sealer was ever used on the sender when it was installed in the head, that could also cause what you are seeing....

LockDoc

**WorkinLonghorn** · 10-23-2018, 06:04 PM

Start at the sending unit (side of the driver side head, near the front on a SBC). Check for a tight connector. In fact check for a connector period. On mine somebody had just twisted the wire around the little post. Then check if that wire is contacting the exhaust manifold. If you have original wire there is sure to be cracking insulation and opportuity for shorts. I think that is where I would start, let us know what you find. -BA

68 P.O.S. · 10-23-2018, 06:55 PM

You have a valve cover leak possibly? I did once and just enough oil got between the sensor and wire connector to mess with the readings similar to yours.

garyd1961 · 10-23-2018, 08:10 PM

When I first put my motor in my truck the gauge would read fine for a while then start jumping to high and back to normal. It would go to high and I could stop turn the motor off and 3 minutes later it would be normal when I started it back up.
I found my problem to be not enough water flow through the heads because I plugged the ports where the heater hoses go. I had a leaky heater core so I just plugged the ports and drilled a hole in my thermostat. The hole helped but it wasn't enough on a long run.
I ran a by-pass hose from my intake to my water pump and it solved the problem. Now I have a new heater core hooked up and it serves as the by-pass.
May not be your problem I know but if you don't have a by-pass hose hooked up I would try it.

**70STOVEBOLT** · 10-23-2018, 08:47 PM

My money is on a short in the printed circuit for the gauge cluster

**DANTIP** · 10-24-2018, 03:37 PM

The wire and connection look good. Looks like we’re down to the sending unit, printed circuit, gauge or fluid level??

**dmjlambert** · 10-24-2018, 07:35 PM

Well disconnect the wire from the sending unit on the engine, and see how it goes. Move the wire around while you have the key on. See how the gauge behaves. If the problem is intermittent, you may need to leave it disconnected for a couple days while you use the truck and observe the gauge. If it's always steady cold with that sender disconnected, then try replacing the sending unit. If the gauge moves while the sender is disconnected, you can connect the sender again. After that put a small piece of post-it note to block the connection of that sender wire where the cluster connector contacts the printed circuit would be the next thing I would try.

**Boog** · 10-24-2018, 08:46 PM

How about the ground wire behind the cluster?

**TBONE1964** · 10-27-2018, 03:18 PM

Hi Dan,

Is this on the cluster I built for you a few years ago?

Let me know if I can help you. I have read above comments and yes it does sound like a connection issue but my other thought is just a wore out temp gauge. They loose there magnetic pull over time and it will allow the gauge needle to flop around like a fish out out of water.

Any issues with the fuel gauge? They do share power from the pink wire at the number #3 location on the cluster connector.

This is not overly complicated. Please feel free to contact me if you need any help moving forward.

Tom

kazoocruiser · 10-27-2018, 03:44 PM

Quote:

Originally Posted by TBONE1964

Hi Dan,

Is this on the cluster I built for you a few years ago?

Let me know if I can help you. I have read above comments and yes it does sound like a connection issue but my other thought is just a wore out temp gauge. They loose there magnetic pull over time and it will allow the gauge needle to flop around like a fish out out of water.

Any issues with the fuel gauge? They do share power from the pink wire at the number #3 location on the cluster connector.

This is not overly complicated. Please feel free to contact me if you need any help moving forward.

Tom

It sounds like you are the one to talk to about clusters. I don't want to hijack the thread, but maybe you can take a second and help me deal with part of what I am doing.

I have a 1981 C-10 and bought a cluster of E-bay that includes gauges and a 100 mph speedometer. I know I will have to change out or add sensors, but what I am wondering is if the replacement cluster is a wire-identical match-up, or will I have to rewire my cluster plug-in to make it work?

Thanks in advance.

Jon

**DANTIP** · 10-30-2018, 11:30 AM

Problem Solved!

I installed an NOS overflow bottle and cap. Once I did that I poured some coolant in the reservoir. I've since added a little more and now it seems stable. Frankly, my radiator didn't look terribly low but apparently I was low on coolant. I'm assuming the sending unit would work correctly when covered with coolant and act up when it was "dry".

Thanks for all the feedback! I also encourage everyone to follow up when problems get resolved. It helps future searchers find answers.

Dan

**70STOVEBOLT** · 10-30-2018, 11:33 AM

Glad you got it sorted out, and thank you for following up. As stated, it can be a huge help to someone having the same issue.

10-23-2018, 01:36 PM	#1
DANTIP Registered User Join Date: Sep 2001 Location: Fort Wayne, Indiana, USA Posts: 1,889	Sporadic Temperature Gauge The temp gauge in my '72 works sporadically and I'm hoping to get some guidance. It reads correctly about 1/2 the time and can change wildly. Sometimes it will be pegged when cold. When driving it can change very quickly and obviously not correctly. Thoughts??

10-23-2018, 02:59 PM	#2
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,582	Re: Sporadic Temperature Gauge Check the wire from the transducer, the gauge and the printed circuit. In my case, I couldn't be bothered and just put in a mechanical gauge that I already had on hand. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

10-23-2018, 03:12 PM	#4
sick472 Registered User Join Date: Jul 2015 Location: Sedalia Mo. Posts: 1,131	Re: Sporadic Temperature Gauge A short anywhere in the circuit can cause the jumping around you are seeing. Hopefully it is a wire that can be fixed/tightened/taped, otherwise it may be the sending unit itself that needs changed out or the circuit board that Stevee mentioned. __________________ He who is without oil shall throw the first rod. Compressions 8.7:1 1972 C10 1976 C10 (parts truck) 1985 K20

10-23-2018, 05:39 PM	#5
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,633	Re: Sporadic Temperature Gauge - If any thread tape or sealer was ever used on the sender when it was installed in the head, that could also cause what you are seeing.... LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

10-23-2018, 06:04 PM	#6
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: Sporadic Temperature Gauge Start at the sending unit (side of the driver side head, near the front on a SBC). Check for a tight connector. In fact check for a connector period. On mine somebody had just twisted the wire around the little post. Then check if that wire is contacting the exhaust manifold. If you have original wire there is sure to be cracking insulation and opportuity for shorts. I think that is where I would start, let us know what you find. -BA __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

10-23-2018, 03:03 PM	#3
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,953	Re: Sporadic Temperature Gauge It's most likely a wiring issue. The sending unit either works or it doesn't; it's rare that they'll work sporadically. What's most likely is that there is either a break or a short in the wire to the sending unit. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

10-23-2018, 06:55 PM	#7
68 P.O.S. Registered User Join Date: Jan 2007 Location: Puyallup, WA Posts: 1,662	Re: Sporadic Temperature Gauge You have a valve cover leak possibly? I did once and just enough oil got between the sensor and wire connector to mess with the readings similar to yours. __________________ 72 C10 lwb fleetside -stock 350/350 combo

10-23-2018, 08:10 PM	#8
garyd1961 Registered User Join Date: May 2016 Location: Henderson NC Posts: 975	Re: Sporadic Temperature Gauge When I first put my motor in my truck the gauge would read fine for a while then start jumping to high and back to normal. It would go to high and I could stop turn the motor off and 3 minutes later it would be normal when I started it back up. I found my problem to be not enough water flow through the heads because I plugged the ports where the heater hoses go. I had a leaky heater core so I just plugged the ports and drilled a hole in my thermostat. The hole helped but it wasn't enough on a long run. I ran a by-pass hose from my intake to my water pump and it solved the problem. Now I have a new heater core hooked up and it serves as the by-pass. May not be your problem I know but if you don't have a by-pass hose hooked up I would try it. Last edited by garyd1961; 10-23-2018 at 08:27 PM.

10-23-2018, 08:47 PM	#9
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,353	Re: Sporadic Temperature Gauge My money is on a short in the printed circuit for the gauge cluster __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear

10-24-2018, 03:37 PM	#10
DANTIP Registered User Join Date: Sep 2001 Location: Fort Wayne, Indiana, USA Posts: 1,889	Re: Sporadic Temperature Gauge The wire and connection look good. Looks like we’re down to the sending unit, printed circuit, gauge or fluid level??

10-24-2018, 07:35 PM	#11
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,805	Re: Sporadic Temperature Gauge Well disconnect the wire from the sending unit on the engine, and see how it goes. Move the wire around while you have the key on. See how the gauge behaves. If the problem is intermittent, you may need to leave it disconnected for a couple days while you use the truck and observe the gauge. If it's always steady cold with that sender disconnected, then try replacing the sending unit. If the gauge moves while the sender is disconnected, you can connect the sender again. After that put a small piece of post-it note to block the connection of that sender wire where the cluster connector contacts the printed circuit would be the next thing I would try. Last edited by dmjlambert; 10-24-2018 at 08:55 PM. Reason: clarity

10-24-2018, 08:46 PM	#12
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,435	Re: Sporadic Temperature Gauge How about the ground wire behind the cluster? __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

10-27-2018, 03:18 PM	#13
TBONE1964 Cluster King Join Date: Nov 2012 Location: Junction City, OR Posts: 5,263	Re: Sporadic Temperature Gauge Hi Dan, Is this on the cluster I built for you a few years ago? Let me know if I can help you. I have read above comments and yes it does sound like a connection issue but my other thought is just a wore out temp gauge. They loose there magnetic pull over time and it will allow the gauge needle to flop around like a fish out out of water. Any issues with the fuel gauge? They do share power from the pink wire at the number #3 location on the cluster connector. This is not overly complicated. Please feel free to contact me if you need any help moving forward. Tom __________________ Contact me on all of your gauge cluster needs. I specialize in restoration, repair and parts sales for 67-72 Chevy and GMC trucks. email me at tbonegarris@yahoo.com I am also a dealer for Counterpart for gauge cluster parts only. Also see my facebook page, CG&C

10-30-2018, 11:30 AM	#15
DANTIP Registered User Join Date: Sep 2001 Location: Fort Wayne, Indiana, USA Posts: 1,889	Re: Sporadic Temperature Gauge Problem Solved! I installed an NOS overflow bottle and cap. Once I did that I poured some coolant in the reservoir. I've since added a little more and now it seems stable. Frankly, my radiator didn't look terribly low but apparently I was low on coolant. I'm assuming the sending unit would work correctly when covered with coolant and act up when it was "dry". Thanks for all the feedback! I also encourage everyone to follow up when problems get resolved. It helps future searchers find answers. Dan

10-30-2018, 11:33 AM	#16
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,353	Re: Sporadic Temperature Gauge Glad you got it sorted out, and thank you for following up. As stated, it can be a huge help to someone having the same issue. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear



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