I have a 1998 nissan maxima. The temperature gauge started off by jumping around from cool (normal) to hot. If I tapped the dashboard the gauge would jump from normal to hot. Now the gauge will gradually rise to hot within a few minutes of driving. 10- 15 minutes. I have not seen other signs of over heating, or at least nothing a novice would see. The upper radiator hose gets hot quickly, the lower hose close to radiator will stay cool and the part of the hose attacked to thermostats gets warm. The radiator buffers were worn with caused the radiator to move around, so I replaced those. I have replaced the Temperature switch and sensor as well as radiator fan. I have a new thermostat at the ready. When I plug in my code reader it shows a coolant temperature of 190* all while gauge is at top line (overheating). I have a stored code, P0400 and a pending code P0105. The engine seems to idle and run fine, not loud or anything i would say would be an issue. The only issue i see is the temperature gauge. Although I am not sure if the entire lower radiator hose should be hot after driving. Can I trust the code reader, is my car really not overheating and the gauge is just broken? Is it safe to drive? I finally got my pre covid job back and really need to know my car is good to go to start on Monday and I can't afford a mechanic until paychecks start coming back in. Any advice would be greatly, GREATLY, appreciated.

As I recall, the thermostat opens at 190 degrees

you say that the temperature stays consistent based on what the code reader says.

I'd say that the car is operating as it should.
Not overheating.

Coolant temperature sensor.

Thermal Transmitter is the one which sends water temperature to cluster. This sensor sits next to ECTS on return coolant block line. ECTS is the one closer to firewall side, TT, closer to radiator side. Page EL-83 (97FMS) shows test for bad transmitter or loose ground in cluster.

P0105 is DTC code of Absolute Pressure Sensor which is bolted to the air duct snorkel. Some excessive voltage detected.

I would check wiring/harness (for short) around the same area first. You may find luck fix one could fix both P0105 and water temp issue.

Good luck.

Excellent information.

Thanks.

The part highlighted here is the ECT sensor.




Where is the Thermal Transmitter you’re talking about?

Virtually next to ECT like loving couple sitting in a park , TT is on the radiator side.

No problem JvG.
Hope Op gives feedback whether it fixes his car issue.

I'm sure it's your gage not the thermal transmitter (Thermo Bulb)

aka Coolant Temperature Sender.