Engine temperature gauge

[Touchdown67]

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?

[spacedebris]

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.

[markeb01]

I’m wondering if you have the correct sender for gauges. According to the offerings at Classic Parts, there’s one sender for gauges and a different part for idiot lights. If you’re running the off/on type for lights that might produce the full hot reading. Here’s 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/

[MikeN]

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/

[m455sx]

Here is my mark for 180 degrees. I used my digital heat sensing gun at the thermostat and sending unit.

[ChevySixty6]

Originally Posted by MikeN

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.

[Touchdown67]

Originally Posted by MikeN

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.

[m455sx]

let me know if that fixes the problem, if so i will buy one.

[amccomb]

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?

[Touchdown67]

Originally Posted by m455sx

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....

[m455sx]

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.

[sandmerchant]

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.

[61_FL_Apache]

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.

[Greg63]

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.

[Breadstick]

Originally Posted by Greg63

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.

[creep]

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.

[dylan1970]

Has anyone found a sensor for stock gauges that is a 3/8 X18NPT?

[The Rocknrod]

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

[vince1]

Internet type in 3/8 NPT heat sensor. Summit sells them.

[shp4man]

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

[sixty4bigwindow]

Reviving this thread.. I have a sensor in my 64 that is from an equus temp gauge, (buddy had the gauge, didn't need the sensor.) Same issue, wired right to the stock gauge, buries on hot.

So if I throw a 13 ohm inline resistor, this should fix my issue of not reading right?

Originally Posted by shp4man

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

[Captainfab]

Why not just get the correct sending unit for your factory temp gauge?

Originally Posted by sixty4bigwindow

Reviving this thread.. I have a sensor in my 64 that is from an equus temp gauge, (buddy had the gauge, didn't need the sensor.) Same issue, wired right to the stock gauge, buries on hot.

So if I throw a 13 ohm inline resistor, this should fix my issue of not reading right?

[The Rocknrod]

https://www.lectriclimited.com/vehic...del/56?cat=734

Temperature Sending Unit $25.00
Part #: 01513321
-original 1/2 x 14 N.P.T.F.-, with factory gauges (correct resistance and connection, produces accurate gauge display) more information

Temperature Sending Unit $34.00
Part #: 01993561
-original 1/2 x 14 N.P.T.F.-, with warning lights Note: Requires a double 56 series female terminal connection more information

[sixty4bigwindow]

Because that would just be too easy lol! Thanks for the links. I am still learning about engines and making things work correctly. I just wasnt sure if it was the sender or the gauge. This makes more sense!

[stsalvage]

Most of the guys that don't like working with the factory gauges are not that smart.They might be old But they like to cut corners.I had this same problem did the same thing.I found out that some time throw the years you have a internal wire fail got hot and burned one of the wires in your fuse block harness.Now you could fend the nest 3 weeks unraveling the back tape to find the problem.But if you install in new factory M&H harness and fuse block that will Fix your problem.I like the factory gauges from 1964--66 Chevy trucks only.I've log more miles on one truck then most of these guys have owned there trucks.Being in the one business that tears up trucks.Mine survived.I have a 1965 3/4 ton 2 speed power glide with a 4.10 gear ran that truck for 17 years and still have it.I have changed almost every part on this truck.The gauges did the same as yours do.But i had a fire in my cab when i was 17 a wire fire.So i only had to deal with the High temp for 1 year when i replaced my full harness with the re pop M&H harness All my problems went away I even got my hi beams back.I was told by the old Farts back when i was a kid never hook up the volt meter.It was a problem child from the start.But i loved my gauges.Never blown a head gasket on my later 1986 350 that i put over 750,000 miles on.I even wore out the fuel pump lobe on the cam.So ya i do be leave i have room to talk about these trucks.I fixed the high reving problem with my 4.56 gear i had i swapped a 4.10 punkin in and put the 235/85/16 tires on i could cruise at 70 only tacking 3000 RPMs Improved my gas mileage as well by going up to 13 from 8 miles per gallon.I even got a guy that was 70 year old put in something extra on my truck that the 1977 1 tons had.When you carrying a load there is a leaver under the bed on the rear end that intensifies the rear brakes.Ya I've done a lot of testing over the last 20 years.Been hit by 3 drunk drivers from behind.So glade i installed a heavy duty hitch and left that heavy bumper.So ya I like factory stuff some times i really works.Plus when you do the maintenance your suppose to do instead of drinking your parts away.