Gauge Reading hot but its not.

[68 Greenie]

Okay guys its Greenie again with the same issue. I bought a thermostat housing with a hole in it to put my temp. sensor in it. I bought a new temp sensor at Napa its a Proformer one its one for our year and its still making my gauge go nuts. I installed a new Edelbrock 750 (had a 600 performer) because I thought it might just be running lean and the shop that built my 383 recommended i step it up to a 750. My radiator cap that has a temp gauge in it says its at 150 along with the gun it shows 152 but my gauge just climbs up and up and up. I have a new aluminum radiator with cooling fans and it worked great along with my gauge with my stock motor. Please someone help me.

[AussieinNC]

The new sender is most likely the wrong one...

Check the cross references at NAPA for an equivalent to 1993369

Also ACDelco G1852 is the correct replacement that seems to be readily available.

Also, make sure the sender unit has a good earth contact to the housing...if the unit has a poor ground, it will read high...if you remove the wire and turn the ignition on, you will see the gauge go to Hot...

[68 Greenie]

Okay Aussie thanks. I will check and see if they have one of those. Im so frustrated with this thing. New motor and can't drive it until I get this figured out.

[HO455]

Originally Posted by AussieinNC

Also, make sure the sender unit has a good earth contact to the housing...if the unit has a poor ground, it will read high...if you remove the wire and turn the ignition on, you will see the gauge go to Hot...

This means the block must have a good ground path to the negative post on the battery. As well as the sensor must make good contact to the housing and the housing to the intake manifold. Too much Teflon tape can give you a poor ground connection as can bolting a well painted housing down with rusty, crusty bolts. Try running an test wire from the sensor body to the negative post when the engine is hot and have someone watch the guage to see if it makes a difference. Remember these guages were never really mention to be accurate but to be used a reference as to what is normal and if you watch it diligently it can give you a heads up that you have a problem. The auto manufacturers prefer you to have an idiot light so you shut the vehicle down if it comes on and then they don't have to replace an engine under warranty. They spent the least money possible so they could charge premium money for the guage upgrade.
Do you have a coolant overflow tank? 150 is an awfully low temperature for your engine to be running at. Where are you measuring the temperature with the gun at? I'm not familiar with a radiator cap for our trucks that have a temperature guage in it. How long of a probe does it have? Is it fully immersed in coolant?

[frank69]

Try putting the sender in the head or in the intake

[Shinysideup]

Originally Posted by frank69

Try putting the sender in the head or in the intake

x2 doesn't belong in the thermostat housing. I also agree its a grounding issue as well.

[67 chevelle]

Did you shoot the temp gun at the block , or thermostat housing ?

[geezer#99]

Your temp sensor won't be accurate on the downstream side of the thermostat.
You got pics of your motor?

[demian5]

Didn't we just go through this?

http://67-72chevytrucks.com/vboard/s...uge+hot+engine

[68 Greenie]

Today I placed my original sensor from my old stock motor (it registered normal with this motor) in the intake of my new motor and I have the same results, gauge just keeps rising. I think it has to be either the printed circuit or the gauge. I guess next on my list will be buying new gauge and circuit. I will try what HO455 said to do and see what I get. Thanks to all for your help.

[68 Greenie]

I do have a coolant overlow HO455. The level pretty much stays the same in it. I bought and aftermarket rad. cap at Oreileys that has a temp gauge built in. I will just buy a better gauge. Do they have one with numbers that will working in the factory gauge cluster? Thanks HO455 you have been a big help. All you guys have been. This site has really been helpful. Thanks.

[HO455]

OK. That's good with a overflow tank the radiator stays full as does the upper hose. With the upper hose full of water then the common issues with using a sensor in the thermostat housing go away. It's how my Burban is set up. You can convert to an aftermarket guage in the bezel but it is not a simple bolt in affair. There are quite a few threads with ways to do it.

[Ed F]

Just for kicks, put a volt meter on your battery with the engine idling and watch it for a few minutes. My '70 had a bad voltage regulator that was allowing up to 17-18 vdc at the battery. I changed the regulator out and it cured several problems including a temp gauge that was reading hot. The longer it idled the higher the voltage got and the higher voltage caused the temp guage to read higher and higher. It also cured a problem with light bulbs burning out prematurely.

[67 chevelle]

Originally Posted by Ed F

Just for kicks, put a volt meter on your battery with the engine idling and watch it for a few minutes. My '70 had a bad voltage regulator that was allowing up to 17-18 vdc at the battery. I changed the regulator out and it cured several problems including a temp gauge that was reading hot. The longer it idled the higher the voltage got and the higher voltage caused the temp guage to read higher and higher. It also cured a problem with light bulbs burning out prematurely.

This has happened to myself also

[demian5]

Originally Posted by 68 Greenie

Today I placed my original sensor from my old stock motor (it registered normal with this motor) in the intake of my new motor and I have the same results, gauge just keeps rising. I think it has to be either the printed circuit or the gauge. I guess next on my list will be buying new gauge and circuit. I will try what HO455 said to do and see what I get. Thanks to all for your help.

Check if the resistor is blown instead of blowing money. Then send me the $250 you would have spent on a gauge and circuit board.

[68 Greenie]

Okay guys update on the gauge reading hot. I read TBone1964 thread about placing the ground wire on the the back of the gauge cluster and it seems to have fixed my problem. I drove it further then I ever have with my new motor and just stayed on the normal mark. Hopefully this is a permanent fix (on my hands and knees praying right now). Thanks to all the members for your help. Much appreciated. If anyone else needs help with this just search "gauge cluster fix its the one by TBone1964.

[HO455]

Excellent work! Glad to hear this issue is behind you. Now go drive the wheels off it