Temperature gauge is jumping, every time rpm goes up 300zx N

[FindJunksCom]

Hello Everyone!

First of, I want to say that I am moderate to expert mechanic, but a newbie when it comes to performance cars.

I just acquired a new project 300zx NA 5spd 1990. It is in the worst possible shape, although I did get a good deal on that. The only thing that worries me, is my temperature gauge always jumping from normal operation temp to 60-80% of the gauge. I noticed that temp(or gauge) rises when I rev up an engine. I do have an OBD2 computer that shows me live coolant temperature, but 1990s using OBD1, which I don't have.

I think it is a faulty cluster, but was wondering if anyone else had this issue and what they've done to resolve it.

Here's the sequence of my actions:

1) Warm up the car to normal operating temperature
(gauge arrow is sitting half way to the HOT)
2) I try to accelerate or rev up without driving
(gauge jumps up as RPM go up, and arrow comes down when I let go of the gas pedal)

[FindJunksCom]

I posted in General section by accident. I created another post one under 300zx. Need to delete this one

[Rogue One]

I posted in General section by accident. I created another post one under 300zx. Need to delete this one

That's ok, I accidentally deleted the one you wanted to keep. Moved this to replace it.

[itsa300zx]

Coolant may be low, air pockets in the cooling system or the sensor and connections are faulty.

check out the z32 wiki site for pics and locations of the sensor.

[ThisIsSparTTa]

I'd start with the wiring diagrams in the FSM and start testing out that circuit. Doubtful the cluster is bad. Also, you can get a Consult to USB connector off Ebay for ~$30 and use ECUTalk for free to pull codes and read all of the sensors. Totally worth it for troubleshooting. You can also spend $100 for ConZult, which is a great program.

Also, know that that there are 2 sensors (look for them on the coolant bypass pipe in front of the timing belt covers). The 2 wire one is for the ECU, and the 1 wire one is for the cluster.

[FindJunksCom]

@ThisIsSparTTa great advice on the 2 sensors by timing belt covers. Will definitely do that first. All my suspicion was that it is faulty or broken cluster, because speedometer and odometer do not work, I think previous owner tried to mingle with the miles.

Good advice, I'll post back my results later