• 2018

Cool Runnings

Thermostat Replacement – 2.4L MultiAir® Engine

The 2.4L MultiAir® engine, commonly referred to as the Tigershark® engine, is the base powerplant for several FCA US LLC models. This leading-edge 4-cylinder engine combines both power and economy for the 21st century. Compared to a traditional engine, the special characteristics of the MultiAir system offer better combustion control and a faster response to torque requests at each cylinder and at every power stroke. The net result is reduced fuel consumption and CO2 emissions. Plus, more power, torque and responsiveness.

The Cooling System

As in other engines, the cooling system regulates engine operating temperature, while also providing a means of heating the passenger compartment. The cooling system is pressurized and uses a centrifugal water pump to circulate coolant throughout the system.

The thermostat helps move the coolant through the engine block. When the engine is cold, the thermostat is closed, allowing the coolant to collect heat. At a pre-determined coolant temperature, the thermostat opens, allowing the coolant to flow through the engine and into the radiator to dissipate engine heat.

The cooling system and its components hold up well over time. It’s not unusual for the water pump, thermostat, radiator and hoses to be serviceable past 100,000 miles, although system maintenance (coolant flush, for example) is recommended. When problems do occur, one of several components might be at fault. For instance, a leaking water pump will lead to engine overheating. A blocked radiator will result in the same condition. Damaged hoses will cause loss of coolant, which is usually easy to see. Thermostat problems, though, are generally easy to detect.

Thermostat Failure

When the thermostat fails, one of two things occurs. One, it stays open. This will increase the time required for the engine to reach operating temperature and closed loop operation. Two, it stays closed. When this occurs, engine coolant cannot circulate and overheating can occur. The temperature gauge on the instrument panel will indicate this with some type of visible warning indicator.

When the thermostat stays open, the driver probably won’t be aware of the delay in reaching closed loop operation. Engine control systems allow near-normal engine performance during the engine warm-up period. This particular problem only comes to the attention of the driver when the engine warning lamp illuminates. The driver is able to fully understand the problem once the vehicle is brought to the dealership and a scan tool reads the Diagnostic Trouble Code (DTC).

The DTC that indicates an issue with the thermostat is P0128, Thermostat Rationality. First, check if there are other DTCs. If not, check the coolant level. If the coolant level is good, check the
thermostat.

Note: Do not perform this test if the engine temperature is above 149°F.

Start the engine. Check the cooling system for proper operation while the engine warms up to operating temperature. Be sure to check the radiator cap, flow through the radiator and anything else that can cause a lack of system pressure or lack of coolant flow. If the cooling system is operating normally, the problem is with the thermostat. Replacement is required.

Figure 1. Thermostat/Housing Assembly

Thermostat Replacement

On most vehicles, the thermostat is contained within a housing, which must be removed to access the thermostat. The design is a little bit different in the Tigershark® engine. In this engine, the thermostat is a part of the housing (see Figure 1). So, when the thermostat is replaced, the entire housing has to be replaced. This includes three components to replace, including the Engine Coolant Temperature (ECT).

Before the thermostat replacement procedure can begin, perform the following tasks:

1. Remove the negative battery cable, engine cover, battery and battery tray

2. Remove the engine cover

3. Raise and support the vehicle, then remove the belly pan

4. Drain the cooling system

Now, let’s get started. Some ancillary components have to be disconnected and removed in order to access the thermostat housing.

1. Remove the three bolts that attach the Power Distribution Center (PDC) to the body; reposition the PDC out of the way

2. Disengage the wire harness retainer from the upper radiator inlet hose at the thermostat housing

3. Loosen the CLIC E® type clamp using tool P/N 10288, then remove the upper radiator inlet hose from the thermostat housing

4. Remove the engine vacuum pump

5. Release the lock holding the shift cable; remove and reposition the shift cable

Figure 2. Thermostat Removal

Now, we have clear access in order to remove the thermostat housing. Refer to Figure 2.

6. Unlock and disconnect the ECT sensor harness connector (4)

7. Disconnect the quick-connect coupling and remove the degas hose (5) from the thermostat housing

8. Remove the two bolts (2) from the intake manifold upper support bracket (1)

9. Loosen, but do not remove, the bracket nuts (3); loosening the bracket (1) will allow the bracket to be repositioned in order to remove the housing

10. Disconnect the quick-connect coupling and remove the heater core inlet hose from the thermostat housing

11. Remove the bolt, then reposition the coolant return tube loop clamp

Now, with clear access to the thermostat housing, the housing can be removed. Refer to Figure 3.

12. Remove the remaining thermostat housing bolts (2), then remove the housing (1) (a swivel socket or ratcheting wrench might be helpful for this task)

Let’s install the new thermostat housing in the engine.

1. Rotate the coolant return tube loop clamp at least 45° away from the thermostat housing mounting surface

2. Pull the intake manifold upper support bracket slightly away from the engine and install the thermostat housing

3. Rotate the coolant return tube loop clamp back into position against the thermostat housing

4. Install the four thermostat housing bolts hand tight

Refer to Figure 2 to complete the installation of the thermostat housing.

Figure 3. Thermostat Removal

5. Install the two bolts (2) to the intake manifold upper support bracket hand tight

6. Tighten the intake manifold upper support bracket nuts (3) to the proper torque spec

7. Tighten the intake manifold upper support bracket bolts (2) and the three other previously installed thermostat housing bolts in a criss-cross pattern to the proper torque spec

8. Connect the ECT sensor harness connector (4)

9. Install the degas hose (5) and connect the quick-connect fitting

10. Bend the coolant return tube loop clamp end tab to secure the thermostat housing bolt

11. Install the heater core inlet hose and engage the quick-connect coupling

12. Install the shift cable and engage the lock

13. Install the engine vacuum pump

14. Install the upper radiator inlet hose using the CLIC E® type clamp using tool P/N 10288

15. Engage the wire harness retainer

16. Install the power distribution center

17.Install the ancillary components, then fill the cooling system

A quick note is in order regarding engine coolant for the Tigershark engine. This engine requires Mopar® OAT (Organic Additive Technology) coolant (it has a purple color). This coolant has a service life of 10 years/150,000 miles. Do not mix any other coolant with OAT coolant. Engine damage and decreased corrosion protection can result.