Temperature gauge fluctuating

[72turbojet]

Recently the temp gauge in my 72 has been fluctuating from normal temp to a hotter reading. My first instinct was the thermostat so I replaced it yet still had the same problem. I checked the temp with a temp gun when the gauge showed both hot and normal reading and the engine is staying at a consistent upper 180s. I also tried a new sensor and have had no success so far. Any ideas what could be causing this? I know it's not my headers because it was fine for a long time until just recently and nothing looks out of the ordinary under the hood

[Andy4639]

Have you checked the water level lately?

[1968aj]

if your temp is normal the only thing left is the gauge itself. some peope say a 160 thermostat does not help but I put one in mine and temp never exceeds the 1/4 mark and heater still works.

[special-K]

If coolant was low the actual temp will fluctuate. But, you say the gun said the temp is consistent. I'm thinking you have a short or a ground issue. If you ground out the sensor wire it will spike all the way up. I would start with pulling the instrument panel, check printed circuit for general condition first. while in there check to see if panel is grounded well to body metal.

[leftybass209]

Originally Posted by special-K

If coolant was low the actual temp will fluctuate. But, you say the gun said the temp is consistent. I'm thinking you have a short or a ground issue. If you ground out the sensor wire it will spike all the way up. I would start with pulling the instrument panel, check printed circuit for general condition first. while in there check to see if panel is grounded well to body metal.

It is possible it's a ground issue, but usually things with a common ground all go faulty together. In this case, dash lights will cut in and out, or not work at all, and the fuel gauge could have issues, and also the Tach if equipped.

By fluctuating, do you mean it's slowly dropping and climbing, or is it spiking low or high and returning? A spike would almost certainly be a ground issue, but slowly fluctuating could be an intermittent high resistance from a poor connection, low coolant, faulty gauge, or incorrect temp sender.

Where did you purchase the temp sender, and do you know the ohm rating on it? Parts stores RARELY ever carry the correct sender.

[72turbojet]

Originally Posted by leftybass209

It is possible it's a ground issue, but usually things with a common ground all go faulty together. In this case, dash lights will cut in and out, or not work at all, and the fuel gauge could have issues, and also the Tach if equipped.

By fluctuating, do you mean it's slowly dropping and climbing, or is it spiking low or high and returning? A spike would almost certainly be a ground issue, but slowly fluctuating could be an intermittent high resistance from a poor connection, low coolant, faulty gauge, or incorrect temp sender.

Where did you purchase the temp sender, and do you know the ohm rating on it? Parts stores RARELY ever carry the correct sender.

It slowly fluctuates, its never had a quick spike. It seems to like rise a little the higher the speed I drive which sounds like a header issue but it has been fine for a long time before this and I still catch the needle going back down on the freeway once in a while