A few years ago, during the ATRA seminar, we discussed the additional coolant temperature sensors added to numerous vehicles and why that change was implemented. As we discussed, the change included adding 3-8 coolant temperature sensors across various engine applications.
The cooling system is not only used to control the temperature of the engine, transmission, and power steering system, but also some of the electronics on several vehicles. When manufacturers discuss the cooling systems in today’s vehicles, they refer to the system as an “Active Thermal Management control system” (ATM) rather than a cooling system, because it is not as simple as a thermostat, water pump, coolers, and some lines. Today’s systems separately regulate the temperature of the components as well as the volume of flow through each component. This means that how you diagnose an issue related to temperature control has dramatically changed.
Let’s look at a couple of systems as examples: the GM 2.0L (RPO LSY) and the 2.7L (RPO L3B). The system prioritizes when and which components receive coolant. The updated system is quite different from other cooling systems you have dealt with in the past.
Changes include:
A split cooling system, including the exhaust manifold, is integrated into the cylinder head. The new manifold design can direct heat to different components. The coolant flow can be individually controlled for the transmission and engine heat exchangers, other areas of the engine, and the passenger compartment heater cores.- Electric variable speed/flow water pump (Figure 1).
- Coolant flow control valving and valve position sensor (Figure 2).
- A coolant bypass system, as these applications do not use a thermostat
- The engine and transmission heat exchangers utilize three modes of operation: No flow to the heat exchanger, Hot coolant flow to raise the temperature of the fluid/oil, and cool coolant flow to reduce the heat of the fluid/oil (Figure 3).
- 8 different coolant temperature sensors are used: Engine block, Engine cylinder head, Engine Inlet, Engine Outlet, Engine oil 1 and 2, Transmission Fluid, and Radiator outlet
- The ECM, BCM, and TCM share the input information from various sensors to determine the operation of the system.
Like conventional systems, these applications use a radiator with a built-in transmission cooler, variable-speed radiator fans, variable-flow air shutters, and a coolant surge tank.
The center of the system redesign is the ECM-controlled “Coolant Flow Control Valve Assembly”. The valve is bolted to the side of the engine and is used to direct which components receive coolant, as well as the volume of coolant fed to each area. The valve consists of a “Main Rotary Valve” and a “Block Control Valve”.
The Main Rotary Valve controls the flow to the radiator, bypass port, and the oil/fluid heat exchangers. The Block Control Valve controls which areas of the block and head are fed coolant. The water pump is located on the bottom right side of the engine on the 2.7L and on the bottom left side of the engine on the 2.0L. The pump is a modulated electric motor that can operate at speeds from 300 to 6250 RPM. The speed of the pump is controlled by the ECM via a Local Interconnect Network (LIN network). The pump speed is strictly based on ECM inputs rather than engine speed, unlike the previous design systems.
The updated design means that the cooling system may be working correctly for one portion of the system, but yet malfunction for another portion of the system. For example, if the oil/fluid flow is limited, you may have oil or fluid temperature issues even though the system appears to be operating normally elsewhere. This means a scan tool and a handheld temperature gun are essential for diagnosing this system.
Another service-related area has also changed with the advent of this system: the coolant filling procedures. These systems are more difficult to fill than a conventional system. Most active thermal management systems have an ‘Automatic Service Fill” procedure that utilizes a scan tool or on-board controls to activate the process. This procedure will cycle the pump and valves to eliminate air from the system after cooling system service or after adding coolant.
Well, as you can see, this job is not getting any easier, and that is why it is important to stay up on the changes that are happening. Until next time, remember: “A car is not just metal, it is a dream on wheels.”
