67-69 Ralleye Temperature Gauge

[bc67barracuda]

Temperature gauge won't go past the first mark when at normal operating temperature. Replaced with new IVR, temperature sending unit, thermostat and when grounded pegs all the way to the far right. Not sure if there is additional testing or is the gauge shot?

 

[harrisonm]

OK, If the temp gauge pegs when the temp sensor wire is grounded (I assume that is what you meant), the gauge is working. However, is the proper amount of voltage going to the gauge? A properly working IVR will send about 5 volts to the gauge. So as the engine warms up, the temp sensor allows more current to flow through to the grounded engine. The warmer the engine, the more current. That current flows through the gauge (the gauge has 2 terminals on it; power in, and power out to the temp sensor. So the more current the temp sensor allows to flow through the gauge, the more movement there is in the gauge. The current inside the gauge flows through a bi-metal spring which provides the needle movement. So if the IVR is not putting out about 5 volts, then the gauge won't show much movement even if the temp sender is allowing max current flow. The gauge can be tested with a few flashlight batteries, if it is taken out. 3 volts will result in a needle movement of about 50-60%. Also, are you sure the engine is warming up? Could the thermostat be stuck open? You may neer an IR thermometer for this. They aren't that expensive, and you will wonder how you ever got along without it.

 

[RedFish]

We rarely read any background info, "It worked fine a few days ago" ? "Worked fine before... engine swap, inst' panel restore" ? Anyway.... 2 things you need to check;
You need zero resistance from the senders body and the neg' battery terminal.
And HOT water of course. A customer sent his temp gauge back because he refused to believe his engine was running a bit too hot. Is yours running too cool ? Hope this helps

 

[bc67barracuda]

We rarely read any background info, "It worked fine a few days ago" ? "Worked fine before... engine swap, inst' panel restore" ? Anyway.... 2 things you need to check;
You need zero resistance from the senders body and the neg' battery terminal.
And HOT water of course. A customer sent his temp gauge back because he refused to believe his engine was running a bit too hot. Is yours running too cool ? Hope this helps

Sorry Ben to bring you out of retirement and that you have answered this question many times before. As mentioned there is a new IVR gas guage, temperature sending unit and a 160F/71C Thermostat. I did however replace the electrical end piece on the temp sending unit with one that attaches to the back of the instrument cluster..so not sure if this is limiting the voltage??

 

[RedFish]

That little bit cut off of a noise cap' isn't a typical copper wire. Pretty sure its steel.
I dont think there is any resistance in it though. You could check from the terminal back to bulkhead.

 

[bc67barracuda]

That little bit cut off of a noise cap' isn't a typical copper wire. Pretty sure its steel.
I dont think there is any resistance in it though. You could check from the terminal back to bulkhead.

There was a break in the wire so I decided to cut it, directly place the wire end on the temperature sending unit and no change in the temperature reading.

 

[RedFish]

So is this a all new build ? Electric fans or anything that might prevent hotter water ?
One of the infrared heat gun things will give you an idea what the temp truly is.
As for your OEM gauges, Since there are 4 in a cluster, It's pretty common for a driver to tap on that glass as if that would effect a suspected faulting gauge. What does happen is the matting frame behind that lens breaks away from its pizzy plastic stakes and falls against the gauges. Everything from wrecked needles to sparks flying occurs.
Why I typed all this... I see what just might be paint broken from the needle in your oil pressure gauge. Could be that zero resistance can generate enough heat to move the needle through a full swing but normal range of resistance and generated heat cannot.
So much tongue wagging

 

[bc67barracuda]

Yes this is a new engine rebuild, 3 or 4 core rad upgrade with no electrical fans. Not overly concerned about the car overheating just annoying not knowing the normal operating temperature. Both upper and lower rad hoses are of equal temperature and the heater blows put warm air. I've even tried burping the system as well???

 

[bc67barracuda]

OK, If the temp gauge pegs when the temp sensor wire is grounded (I assume that is what you meant), the gauge is working. However, is the proper amount of voltage going to the gauge? A properly working IVR will send about 5 volts to the gauge. So as the engine warms up, the temp sensor allows more current to flow through to the grounded engine. The warmer the engine, the more current. That current flows through the gauge (the gauge has 2 terminals on it; power in, and power out to the temp sensor. So the more current the temp sensor allows to flow through the gauge, the more movement there is in the gauge. The current inside the gauge flows through a bi-metal spring which provides the needle movement. So if the IVR is not putting out about 5 volts, then the gauge won't show much movement even if the temp sender is allowing max current flow. The gauge can be tested with a few flashlight batteries, if it is taken out. 3 volts will result in a needle movement of about 50-60%. Also, are you sure the engine is warming up? Could the thermostat be stuck open? You may neer an IR thermometer for this. They aren't that expensive, and you will wonder how you ever got along without it.

A new gas gauge / IVR has been installed. Thought the thermostat may be stuck as well so I did replace with the same one(160F/71C Thermostat). Upper & lower rad hoses have equal heat and it does pump out warm air. I have taken the dash out several times so I consider an expert in this area...I might just try to find a new temp gauge on E-Bay. Thanks for you info!

 

[cudascott]

The upper hose should be hotter than the lower hose

 

[mopardude62]

I had this same problem. It wound up being the sending unit was the one for the idiot light not the gauge.

 

[bc67barracuda]

That might explain it. Worth looking into as it is a cheap part. Thanks

 

[AJ/FormS]

Temperature gauge won't go past the first mark when at normal operating temperature. Replaced with new IVR, temperature sending unit, thermostat and when grounded pegs all the way to the far right. Not sure if there is additional testing or is the gauge shot?

Old post I know, but I thought it was worth responding to, at least for the next guy hitting the search button.

So see if I understand this right;when you take the wire off the sender and ground it to the block, then the needle climbs to the top. Have I got that right?
And while the engine is warming up, the needle moves from somewhere on the bottom, up to about the first mark. Have I got that right?
If yes,and yes, then the answer is simple; the gauge is responding, and the sender is sending.
Now whether or not either of them is doing the right thing, I cannot say.
But I would suspect the sender, so
-Firstly I would check that the body of the sender is grounding to the engine with near Zero resistance. Some guys put sealers on the threads which don't always pass juice. No sealer is needed on brass senders.
-The next thing I would do is check for a signal coming down the wire. Previously 5 volts was mentioned. While this is sorta correct, you need to put an analog voltmeter on that wire. When you do this you will see a pulsed voltage. The stock dash VR is like a signal flasher, in that it sends battery voltage down that wire for a split second and then turns off. A split second or so later it repeats;just like a signal flasher. The result of this is that the sender interprets this as about 5 to perhaps 6 volts.That's why you sometimes see Dodge temp and fuel gauges doing a little tic-toc dance.
-Ok so we have a signal, cuz the meter climbs to the top.And you cleaned the sender off, or it is grounding right?
-Well the next thing to check is to be sure the sender is actually in the water. Some guys stack up 2 or 3 adapters to fit one in, and it takes 3 months to bleed the air out. These senders do not measure air temp; they have to be in the water.So the water temp has to rise, at the sender, from ambient, to near to the stat rating.
-Ok so finally; the water temp has to change the resistance of the sender from very high to very low, as it heats up.You can measure this resistance change with your ohmmeter. The range of change has to be compatible with your gauge requirements.Certain senders won't work the gauge.