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Old 05-17-2012, 06:26 PM   #1
Touchdown67
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Engine temperature gauge

I have a 65 C10 with factory gauges and a SB400 engine. The problem I am having is the temp gauge goes to almost full hot after about 5 mins run time. I have gone through everything (ie. radiator, water pump) I put in a 195 degree thermostat instead of the 160 it had before. We have checked the temps on all the hoses and the water neck with a temp gun and the temps seem to be between 171- 195 degrees. I bought another sending unit from NAPA and the gauge still shows hot. I am wondering if there is a different sending unit I should be looking for or is the gauge shot. Has anyone encountered the same?
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Old 05-18-2012, 04:51 AM   #2
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Re: Engine temperature gauge

I've never fooled around with the vintage gauges personally. However I did have the same kind of problem with my 89 GMC Jimmy with the temp gauge reading over 240 when the temp gun indicated only 205. In my case it was a bad resistor on my gauge. At the time I was in school for electronic engineering and instead of just buying a new gauge, I replaced the resistor (cost me 95 cents from radio shack), then checked again. gauge read between 205-210 when the heat gun said 205.

Now granted this was with a system over 2 decades later but the older gauges are likely built in the same way, sender sends a signal to the gauge and the reading across the resistors determines how high the needle goes. Since you said you replaced the sending unit, this would be my best guess.
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Old 05-18-2012, 10:20 AM   #3
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Re: Engine temperature gauge

Iím wondering if you have the correct sender for gauges. According to the offerings at Classic Parts, thereís one sender for gauges and a different part for idiot lights. If youíre running the off/on type for lights that might produce the full hot reading. Hereís a photo and link for the gauge sender, followed by the sender for the lights. Also make sure you have no teflon tape on the sender threads which can insulate the circuit and ruin the reading.



http://www.classicparts.com/1956-72-...ctinfo/53-811/



http://www.classicparts.com/1961-66-...ctinfo/53-812/
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Old 05-18-2012, 10:23 AM   #4
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Re: Engine temperature gauge

I had the same problem with the factory temp gauges on both my 64 C10 and my 69 Chevelle. The parts houses sell sending units that are supposed to fit a variety of applications, and they don't work right. I got the proper sending units for both cars from these guys, and both gauges now work perfectly.

http://www.lectriclimited.com/
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Old 05-18-2012, 02:06 PM   #5
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Re: Engine temperature gauge

Yep i have bought several one from napa and one AC delco as well and mine saying it is running hot. Mine is at the very edge of the green line.
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Old 05-18-2012, 02:08 PM   #6
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Re: Engine temperature gauge

Here is my mark for 180 degrees. I used my digital heat sensing gun at the thermostat and sending unit.
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Old 05-18-2012, 02:16 PM   #7
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Re: Engine temperature gauge

Quote:
Originally Posted by MikeN View Post
I had the same problem with the factory temp gauges on both my 64 C10 and my 69 Chevelle. The parts houses sell sending units that are supposed to fit a variety of applications, and they don't work right. I got the proper sending units for both cars from these guys, and both gauges now work perfectly.

http://www.lectriclimited.com/
Well i finally got off my butt and ordered one of these. With shipping it was only $34. I've read several posts in the past about getting the correct temp gauge, but never got " a round to it". It was always one of those " i should probably get one of those". Now i won't have to keep second guessing myself and wondering is it really too hot, or just the gauge.
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Old 05-22-2012, 11:51 AM   #8
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Re: Engine temperature gauge

Quote:
Originally Posted by MikeN View Post
I had the same problem with the factory temp gauges on both my 64 C10 and my 69 Chevelle. The parts houses sell sending units that are supposed to fit a variety of applications, and they don't work right. I got the proper sending units for both cars from these guys, and both gauges now work perfectly.

http://www.lectriclimited.com/
Thank you MikeN... I ordered a sending unit and a horn relay from these guys today.
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Old 05-22-2012, 11:55 AM   #9
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Re: Engine temperature gauge

let me know if that fixes the problem, if so i will buy one.
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Old 07-17-2012, 01:14 AM   #10
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Re: Engine temperature gauge

I dont have a issue with the guage reading to hot. Mine doesnt work at all. When I turn the key on the guage needle moves. But it doesn't work after that, I replaced the sending unit with one from napa, still nothing. Any suggestions?
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Old 07-17-2012, 02:17 AM   #11
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Re: Engine temperature gauge

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let me know if that fixes the problem, if so i will buy one.
Well I put the sender in a few weeks ago with teflon tape and it seems to be reading more accurately. I might pull it back out and remove the teflon tape and see if this makes any difference. But overall it seems to be more accurate. I also bought a horn relay from Lectric and now I have a working horn. Good luck....
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Old 07-17-2012, 08:28 AM   #12
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Re: Engine temperature gauge

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Originally Posted by amccomb View Post
I dont have a issue with the guage reading to hot. Mine doesnt work at all. When I turn the key on the guage needle moves. But it doesn't work after that, I replaced the sending unit with one from napa, still nothing. Any suggestions?
Probably the guage. Is it a factory guage? If so PM me, I have a couple.
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Old 07-18-2012, 06:06 PM   #13
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Re: Engine temperature gauge

I have the same problem on my 64' Suburban 4x4 with a 350. Gauge shows hot when on freeway- right at the end of the green. If it's a hot day, the needle will just start to touch the white line below hot.

This is the temp when running around town.

Because it seemed to only get hot when running high RPM's I thought it might be caused by my lower radiator hose collapsing, but the hose is fine.

Heat gun shows around 180 at the block freeze plugs, the heads run about 5 degrees higher.

I replace the sender twice- once from Napa and once from Brothers, still the same problem.

I never thought about the Teflon tape concern, I will check and remove if I applied it.

If not, I will buy one from the link.
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Old 07-18-2012, 08:18 PM   #14
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Re: Engine temperature gauge

I have this issue with my 61 and I read somewhere the auto parts store senders will not work right. Someone posted a GM part number that is correct for these guages. I dont have the number handy and have not bought one myself yet, but would like too.
I also have a mechanical guage under the dash that works fine so Im good for now and I know im not over heating.
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Old 07-18-2012, 10:08 PM   #15
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Re: Engine temperature gauge

I was told years ago not to put anything on the threads of the sending unit as it interferes with the grounding of the sender and will affect the gauge reading.
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Old 07-19-2012, 08:42 AM   #16
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Re: Engine temperature gauge

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Originally Posted by Greg63 View Post
I was told years ago not to put anything on the threads of the sending unit as it interferes with the grounding of the sender and will affect the gauge reading.
Greg.
I was doing some research on this recently and read this a lot of places, as well.
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Old 07-19-2012, 11:26 AM   #17
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Re: Engine temperature gauge

I put in a sending unit from classicparts and it read really hot so I installed a gauge directly on the motor and it turned out that my motor was actually running hot. After a rad and fan change the motor stays between 180-190 according to the motor mounted gauge and the dash gauge stays right around the middle.
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Old 05-17-2017, 04:27 PM   #18
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Re: Engine temperature gauge

Has anyone found a sensor for stock gauges that is a 3/8 X18NPT?
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Old 05-17-2017, 04:40 PM   #19
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Re: Engine temperature gauge


https://www.lectriclimited.com/faq/
The correct one: https://www.lectriclimited.com/elect...ing-unit-86912
Some info: http://67-72chevytrucks.com/vboard/s...d.php?t=587190
Found in the FAQ section: http://67-72chevytrucks.com/vboard/s...d.php?t=646002
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Old 05-17-2017, 05:55 PM   #20
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Re: Engine temperature gauge

Internet type in 3/8 NPT heat sensor. Summit sells them.
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Old 05-17-2017, 05:56 PM   #21
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Re: Engine temperature gauge

An in line resistor will fix the issue. My truck took about a 13 ohm one.
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