Temp. gauge fluctuates when revving

[Dimorphic]

I recently noticed whenever I start the engine and when I rev then I noticed that temperature gauge goes down and back up after releasing the gas pedal. So when the engine is cool, it is ideally dropped to the bottom, when I rev it would even go lower then when you release the gas pedal, it would go back to the the starting temperature.

As the temperature rises, I keep on revving then it would also simultaneously go down a little every time I step on the gas pedal and when I release the gas pedal it would rise back up again. But when the temperature is stabilized (just below half of the gauge, the normal temperature) it seems pretty normal when I rev.

What at are your thoughts in this issue?

Thanks!

Note: This is in neutral and idle mode on a flat road.

 

[HeX]

What car is this? What engine does it have? When was the last time the thermostat was changed? It may just be a faulty thermostat thats stuck open. If not...

Does it have an engine or gauge cluster swap? Have you inspected any wiring pertaining to the cooling system?

 

[Dimorphic]

What car is this? What engine does it have? When was the last time the thermostat was changed? It may just be a faulty thermostat thats stuck open. If not...

Does it have an engine or gauge cluster swap? Have you inspected any wiring pertaining to the cooling system?

----

Car: Honda Civic 1993 LX ESI
Engine: PH15 carb type
Thermostat: As for the status when it was changed is unknown. But as from previous car seller, the thermostat is OPEN all the time.
Engine Swap?: No, I believe this is the stock Engine as stated on the papers. PH15
Gauge Cluster swap: When I opened the gauge cluster and checked the back, it had no wires/cables. As per technician, he said it was a digital type which has no cables to it.
Wiring for cooling system: As for the wiring, it has been bypassed and the radiator fan has been rewired directly when you start the ignition.

Best regards,

 

[HeX]

I would think the thermostat must be the issue because it should not be open always. Thats a cheap fix so I suggest you do that anyways & see if it eliminates the issue.

Test your coolant temperature sensor because that failing seems to be one of the common reasons why people rig up the radiator fan wiring instead of just changing the sensor.

In regards to you saying "the wiring has been bypassed", does that refer to the rig we just covered or something else?