Revisit coolant temp gauge problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**MikeB** · 03-26-2026, 12:46 PM

I have a 69 bezel with 73-87 electric oil pressure and voltmeter gauges. Both work fine, but I'm not happy with the 69 coolant temp gauge because it's super non-linear.

I have two stock 67-72 and one stock 73-87 temp gauges that I've played with, and a variety of senders and shunt resistors. But with my best combination, the pointer doesn't move off far left until about 150 degrees, but then starts moving quickly to the right.

Fortunately, the pointer is near center when actual temp is about 180-190. But at 210 or so the pointer is far right, not pegged but where you'd think it would be at 230 or higher.

What I'd like to find is a gauge that fits in my panel along with its sender that's a little more linear. Any suggestions.

Here's my calibration standard (!) and instrument panel. Sender is just to the right.

**mr48chev** · 03-26-2026, 01:29 PM

Have you got the correct Delco sending unit for the year model of the gauge? I found on my 77 that all sending units for gauges are not the same.

**MikeB** · 03-26-2026, 02:23 PM

Quote:

Originally Posted by mr48chev

Have you got the correct Delco sending unit for the year model of the gauge?

It's been a while, but seems like there was a range of years that called for the same P/N sending unit. I have three of them from different sources, and they all have a slightly different resistance curves, which I hear is common.

I think the key is the shunt resistor. I may have to buy a cheap decade box to determine the proper resistance. https://www.amazon.com/Elenco-Resist...544182-4011469

I'm OK now with the pointer straight up at 180-190, but am using a resistor in series as well as the shunt resistor, which is kind of a kludge.

**mr48chev** · 03-26-2026, 03:18 PM

My 71 wasn't changed around much before I put the 500 Cad in it and when I swapped the broken 350 for another one I used the old sender that is now in the 500. On the 77 C 10 it had a hard life as a work truck though untold changes over the years. At one time it pulled goosneck trailers, It has a flat bed with air line connectors on it and it has a 10 ft flatbed with a hoist. The wiring for the stop and taillights is a yellow extension cord like is used on construction jobs. No telling on the sending unit that I took out of it but you can bet it was the cheap one as far as price range went at the parts house.

**PbFut** · 03-26-2026, 06:52 PM

Aftermarket sending units are hit and miss for the factory gauge. Best to find a correct AC Delco for year of gauge or used. Location will affect as well. Right side rear will be hotter than left side front. The port you have the dial gauge in picture in the tStat housing area of the intake manifold will be a bit finicky on cold startups. I found it took about a week of regular driving to finally get all the air bubbles completely out of my new BPE small block 400. Until I got ALL the bubbles out, the factory and aftermarket ECU would see swings at stop lights and cruise, especially during warm up. I used multi high flow stats with and without bypass holes. Fooled with the heater valve and other tricks. None fully cured and then over time, all issues subsided as the bubbles finally cleared.

67swb72klb · 03-29-2026, 09:58 PM

I saved this from a thread on here some time ago...

**MikeB** · 03-30-2026, 01:48 PM

Quote:

Originally Posted by 67swb72klb

I saved this from a thread on here some time ago...

It's been several years, but I remember doing some things using those images as a guide.

Can't find my spare gauge, but did find an 88 ohm factory-type resistor!

**mike16** · 03-30-2026, 02:32 PM

Sealants and the such can cause fluctuations in resistance

03-26-2026, 12:46 PM	#1
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 4,035	Revisit coolant temp gauge problems I have a 69 bezel with 73-87 electric oil pressure and voltmeter gauges. Both work fine, but I'm not happy with the 69 coolant temp gauge because it's super non-linear. I have two stock 67-72 and one stock 73-87 temp gauges that I've played with, and a variety of senders and shunt resistors. But with my best combination, the pointer doesn't move off far left until about 150 degrees, but then starts moving quickly to the right. Fortunately, the pointer is near center when actual temp is about 180-190. But at 210 or so the pointer is far right, not pegged but where you'd think it would be at 230 or higher. What I'd like to find is a gauge that fits in my panel along with its sender that's a little more linear. Any suggestions. Here's my calibration standard (!) and instrument panel. Sender is just to the right. Attached Images __________________ Mike 1969 Custom/10 LWB -- owned for 37 years. 350/TH350, 3.08 posi, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. Hedman stainless headers. Old Air installation in progress. 1982 Custom Deluxe 10 SWB -- converted from 250-six to roller cam 350 w/ Vortec heads -- sold 1981 C10 Silverado LWB, 305, TH350C -- sold, but wish I still had it! 1969 C10 (not the current one) which I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 26 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

03-26-2026, 01:29 PM	#2
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 16,391	Re: Revisit coolant temp gauge problems Have you got the correct Delco sending unit for the year model of the gauge? I found on my 77 that all sending units for gauges are not the same. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around. Last edited by mr48chev; 03-26-2026 at 01:46 PM.

03-26-2026, 03:18 PM	#4
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 16,391	Re: Revisit coolant temp gauge problems My 71 wasn't changed around much before I put the 500 Cad in it and when I swapped the broken 350 for another one I used the old sender that is now in the 500. On the 77 C 10 it had a hard life as a work truck though untold changes over the years. At one time it pulled goosneck trailers, It has a flat bed with air line connectors on it and it has a 10 ft flatbed with a hoist. The wiring for the stop and taillights is a yellow extension cord like is used on construction jobs. No telling on the sending unit that I took out of it but you can bet it was the cheap one as far as price range went at the parts house. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

03-26-2026, 06:52 PM	#5
PbFut Senior Member Join Date: Feb 2022 Location: Ca Posts: 1,024	Re: Revisit coolant temp gauge problems Aftermarket sending units are hit and miss for the factory gauge. Best to find a correct AC Delco for year of gauge or used. Location will affect as well. Right side rear will be hotter than left side front. The port you have the dial gauge in picture in the tStat housing area of the intake manifold will be a bit finicky on cold startups. I found it took about a week of regular driving to finally get all the air bubbles completely out of my new BPE small block 400. Until I got ALL the bubbles out, the factory and aftermarket ECU would see swings at stop lights and cruise, especially during warm up. I used multi high flow stats with and without bypass holes. Fooled with the heater valve and other tricks. None fully cured and then over time, all issues subsided as the bubbles finally cleared.

03-29-2026, 09:58 PM	#6
67swb72klb Registered User Join Date: Dec 2010 Location: livingston co.mi Posts: 2,559	Re: Revisit coolant temp gauge problems I saved this from a thread on here some time ago... Attached Images __________________ California 65 GTO---Texas 64 burb 283 ---Oklahoma 67 CST SWB BBW wood bed 327 2004r---New Mexico 72 k10 350 350 auto---Georga 72 short step project

03-30-2026, 02:32 PM	#8
mike16 Senior Member Join Date: Dec 2009 Location: bisbee, arizona Posts: 1,609	Re: Revisit coolant temp gauge problems Sealants and the such can cause fluctuations in resistance



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