Why this sensor matters
Your ECU uses coolant temperature for cranking fuel, warm-up enrichment, idle speed, ignition corrections, thermo fans and overheat protection. A sensor in the wrong place, or one sitting in an air pocket, will give a reading that lags or lies, and the engine will start and warm up badly no matter how good the tune is.
Haltech's sensor is an industry-standard thermistor with a solid brass tip. It screws into a threaded hole so the tip sits in the flow of coolant. Many engines already have a port that suits it.
Choosing a location
- Before the thermostat. Mount the sensor on the engine side of the thermostat, where it sees the engine's own coolant temperature even while the thermostat is closed. After the thermostat, the reading stays cold until it opens.
- In real flow. The tip needs to be in moving coolant, not a dead-end pocket.
- Use an existing hole if you can. Most engines have factory sensor ports, and one of these is usually the easiest option. Drill and tap a new hole only after confirming you'll reach the coolant passage.
Picking a thread
| Sensor | Thread |
|---|---|
| Small thread (HT-010300) | M12 x 1.5 |
| Large thread (HT-010302) | 3/8 NPT |
| 1/8 NPT (HT-010304) | 1/8 NPT |
Air-cooled engines
No coolant? You can mount the sensor directly into the engine block to read metal temperature, or use it to read oil temperature instead. Either way the ECU still gets a useful engine temperature for warm-up and protection.
Fitting it
- Drain enough coolant to get below the sensor port if needed.
- Fit the sensor with a suitable thread sealant. Don't over-tighten into an aluminum head.
- Refill, then bleed the cooling system using the method in the factory service manual. Trapped air around the sensor gives false readings.
- Run the engine up to operating temperature, let it cool, and top up the coolant if the level has dropped.
On a cold engine that's sat overnight, coolant and air temperature should read close to each other. If they don't, check the calibration and pull-up settings in Coolant Temperature Sensor setup. The matching install guide for air temp is Inlet Air Temperature Sensor.
