Looking for some help with a temperature gauge that points all the way to the right showing hot. I have verified the engine is running at 180. I have replaced the sender twice and and the gauge still shows hot.The first replacement sender was from WCCC and the last sender was a genuine Motorcraft. Car is a 72 XR7 Conv. with a 351C. Car has 26K total miles. Any help would be appreciated.
You need a gauge tester to know for sure. You should unplug the sender first. It should drop below cold. Otherwise the wire may be shorted to ground
That’s the puzzling part. if I unplug the sender the gauge goes to zero. If I ground the sender the gauge goes to hot. It almost like the the sender is not matched to the gauge if that is possible.
Don sells a gauge tester at WCCC… sounds like the perfect candidate for one…
Is it possible that the sending unit and the gauge are not matched?
That’s the typical issue. Modern sending units are totally wrong values. The OEM ones are the only ones that work for me.
More here: Pet Peeve - Parts Store sending units
So the wire is not shorted. Be careful grounding that wire as it shorts out the gauge and it will burn up. Unless you know the gauge is accurate you can throw senders at it and never know what works.
The last sender I installed is a Motorcraft # SW-2328. According to my local parts store this is the sender that it call for.
If it was made recently it’s not even close to being correct. You have identified the problem.
Do you know what the correct sender would be?
You need to verify that is your problem first by using a temperature measuring device and an ohm meter. 99% I think that’s your problem but you shouldn’t buy anything until you know for sure.
Check ground wire from engine block to car body
Had same problem ground wire was loose!
Chuck, I will give that a try. This car has 26,000 original miles and has been stored inside for the last 35 years. I can run a temporary wire to the body and see if that helps. Thanks !
First… chasing the sending unit rabbit hole is useless…second…verify your voltage limiter is working…you will need an analog voltmeter for this…or attach a 12 volt low wattage bulb between the sending unit wire and ground…if it blinks…you are probably ok…(assuming you have an old style VL…if it’s a newer electronic style…a digital voltmeter will work…if all this checks out then the gauge is the culprit…it needs calibration…this is the preferred fix if you are not open to a short cut. If you are and I assume you have thought about it…read on…
You need to add resistance to the circuit…but how much??.. no worries…order a variable resistor from Amazon…0-25 ohms…they come in packs of 2 for about $14. They have 3 terminals but you are only concerned about the center one (to sending unit… although it probably doesn’t matter) and one of the side terminals (gauge wire in). The beauty of this is that you can test it under the hood then in stall it under the dash. Get the engine to operating temp…verify it’s not running hot then dial in the resistance you need to bring the pointer to the appropriate position. If your outgoing coolant is 180 and lower hose temp is145ish then shoot for mid position or scantly lower…sorry I was so long but I just went through this with my latest project.
If the fuel and oil pressure gauges are reading more or less accurately then the instrument voltage regulator is working as it feeds all of the gauges.
This leaves us with two possibilities. The gauge is out of calibration or the sender is mismatched to the gauge. The highest probability is the sender, but you have already thrown money at that with no success.
This is like solving an equation, you have to have at least one known quantity. This is where the gauge tester comes in. It will supply the correct resistance in place of the sender so you can see what is actually the problem. From testing a large sample of gauges, a little less than 30% are off. Some more than others. The gauge tester is $30 including free shipping in the US.
If the gauge is off, send it to Rocketman RCCI for calibration. It’s only $15.
If it is the sender get an original off of Ebay.
Redxr7 you are right that the resistance is too low causing the gauge to read high. However the problem is that the senders are non linear. So on either side of the point you are adding resistance to, the gauge will be even less accurate. The temp sender is a thermistor and the shape of its resistance curve is not a straight line. At HOT it should be 10 ohms or slightly less. When you add resistance at the middle it will no longer get down to 10 at the high end so the car can be overheating and the gauge is still reading cool. If you want to see this in action, use the variable resistor to sweep the gauge through its range. You will see that very small changes produce big changes in reading at the high end and it takes big changes in resistance to change things on the bottom end.
check your connections. I installed an aftermarket one and it was doing the same thing. Turned out my I was plugging it incorrectly. Soon as i figured out were it should really be connected it worked perfect
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I’ve had more than 50 of these '67 and '68 Cougars - none has ever had a bad instrument voltage regulator. I don’t doubt that one could fail but from my experience it’s not likely.
You have to start by knowing something - the temperature when the engine is hot or cold is the first thing that you need to establish. A meat thermometer, infra red thermometer, candy thermometer - someone you know has one and will loan it to you for free. Buying random stuff is never going to do it.
I have tried two different temperature senders with both giving incorrect readings. The newest sender being a Motorcraft from SW .The Oil, Gas and Voltage gauges read correct. I have installed a 180 degree thermostat. When the engine comes up to operating temperature which I have just recently verified with two different infared measuring guns taking a reading at the top of the radiator. When the engine comes up to operating temperature the gauge goes to full hot. After a few minutes it settles back to just past the full hot mark on the gauge.
I have doubled checked the wiring and found no flaws. If all the other gauges are reading correct can we eliminate the Voltage regulator as being the problem?
If the fuel gage reads properly then the sender is the problem. If you buy the right one instead of multiple wrong ones then you will only have to buy one. basic 10884 This one:
[Temp Sender - scroll down it is listed as “1970” but will work for 1967 - 73.](https://basic 10884)
Have you tested the gauge? You have to know that one part of the circuit is good. You are correct that if the other two gauges are correct then the IVR is good