Why is my engine overheating rapidly

On a Nissan D21 (Hardbody), the coolant temperature sensors are typically screwed into the intake manifold near the thermostat housing, toward the front of the engine.

There are usually two sensors in this area, and it is easy to mix them up:

• For the ECU/Engine Computer: This sensor has a 2-wire electrical connector.
• For the Dashboard Gauge: This sending unit has only a single wire (often yellow and red) attached to a male spade terminal.

Note: Depending on your exact engine (like the V6 VG30i), there may also be a separate cylinder head temperature sensor on the driver's side of the engine.

So, like any problem it could be a number of things. First, u must verify that the engine is really overheating. Check the water level, check the temp of the water, use an IR sensor or other device to check the engine temp. Bottom line is one of the above snesors could be bad = if the dash guage is the indicator, there is one sensor specifically for that, so check the temp via the ECU since it uses a diff sensor.