There are TWO temp sensors on the 4.0L: one for the gauge (single wire) and one for the ECU (two-wire). Confusing each other causes diagnostic chaos.
The 4.0L has two coolant temperature sensors and they serve different purposes. The single-wire sender on the thermostat housing drives the dash gauge only. The two-wire sensor (or two single-wire sensors on Renix) on the front-passenger side of the head feeds the ECU for fueling and timing. Symptoms of a failed ECU coolant sensor: hard cold start, poor fuel economy, rich/black smoke, P0117/P0118 codes. Symptoms of a failed gauge sender: incorrect or pegged-cold dash gauge while engine actually runs at normal temp. Sensors are cheap ($10-25). Mopar 56027872 is the two-wire ECU sensor for HO; the single-wire gauge sender is Mopar 56027873. Both are 3/8 NPT thread. Drain a quart of coolant before pulling so you do not lose much. Apply thread sealant or use a sensor with sealant pre-applied. Torque to 10-15 ft-lb - they are straightforward to crack.
| Part | Vendor | Est. price |
|---|---|---|
| ECU CTS Mopar (two-wire) | Mopar | ~$25 |
| Gauge sender (one-wire) | Mopar | ~$20 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.