Electric Thermostat
| ITEM | DESCRIPTION |
|---|---|
| 1 | Coolant pump connection |
| 2 | Engine coolant outlet tube connection |
| 3 | Heater element electrical connector |
| 4 | Radiator lower hose connection |
| 5 | Coolant expansion tank connection |
The electric thermostat is a multi-stage device, located in front of the cylinder block, beside the coolant pump inlet to provide fast response and control of the engine outlet temperature. The electric thermostat comprises a thermostat and a resistance heated wax element in one housing, which is not a serviceable item and it can be replaced as an assembly.
The thermostat housing has 4 connections. The lower connection receives a quick fit connector which receives coolant from the radiator lower hose and the ATF cooler. The upper hose connection is connected to the engine coolant outlet tube. The flow from this connection is governed by the thermostat. The larger connection at the side provides coolant flow to the coolant pump and the smaller connection at the side receives coolant from the heater core and the coolant expansion tank.
The thermostat allows rapid engine warm-up by preventing coolant flow through the radiator and by limiting coolant flow through the cylinder block when the engine is cold. During warm-up and at engines speeds above approximately 1800 RPM, a by-pass valve opens to control the coolant flow and pressure, to protect the engine components. When the thermostat opening reaches 6 mm (0.24 in.), the by-pass flow is shut-off. When the thermostat opening exceeds 6 mm (0.24 in.), the radiator coolant flow is further controlled up to the point where the thermostat is fully open. At this point maximum radiator coolant flow is achieved to provide maximum cooling.
The thermostat begins to open (with ambient temperatures of 15-35°C (59-95°F)) at 98-102°C (208-215°F) and is fully open at 108°C (226°F).
The electrically heated thermostat is used to regulate the engine coolant temperature by the powertrain control module (PCM). The increased wax temperature provides higher coolant temperature during part load conditions and at low speed cycles. The increased coolant temperature results reduced friction in the engine, improved combustion in the cylinders, and reduced fuel consumption and emissions. An electric thermostat heater element assembled within the wax element to regulate the engine coolant temperature during high load conditions and speed points to protect the engine from thermal overload.
Operation of the electric thermostat is controlled by the PCM upon the following inputs:
- Engine load
- Engine speed
- Vehicle speed
- Coolant temperature
- Intake air temperature
The electric thermostat has a battery feed from the right engine junction box (EJB) located in the right front of the engine compartment, a switched power supply from the PCM relay, located in the left EJB a hardwired connection to the PCM and a ground connection. If the PCM starts to regulate the system, the PCM supplies a ground path for the heater element in the electric thermostat. This causes the element to expand and increase the opening dimension of the thermostat.