![]() When the air flow through the condenser or radiator is restricted by organic debris, use soap and low-pressure water to remove it. Photo 4: This Subaru A/C condenser is relatively clean. Following Subaru’s coolant maintenance schedule will drastically reduce radiator clogging and leakage. Although the service lives of most OE coolants extend well past 100,000 miles, the coolant additive packages designed to prevent both chemical and electrolytic corrosion eventually become degraded to the point that the coolant itself can corrode the radiator core. Most Subaru radiators, as with most import radiators, use cooling tubes with very thin cross sections that easily clog with scale or even some types of granular cooling system sealants. The diagnostic solution for this condition is to install either an OE thermostat or a reliable aftermarket brand of thermostat. While we’re discussing coolant flow, be aware that some cheaper aftermarket replacement thermostats can restrict coolant flow on Subarus because their physical dimensions are too small, or their opening temperature isn’t calibrated correctly. ![]() If a Subaru’s overheating problem is symptomatic with highway speeds or climbing a steep incline, it’s usually because coolant flow is restricted through the radiator. Photo 3: Thoroughly inspect the space between the radiator and A/C condenser for accumulations of leaves and inspect for coolant leakage around the tank gaskets, as well. Allowing for some technical inaccuracies, both readings should be within 10 degrees of each other. Use a non-contact pyrometer to compare actual water outlet temperatures with the PID values displayed on the scan tool. One of the most important PIDs is the engine coolant temperature (ECT) sensor data. While scrolling through parameter indicator in display (PID) values displayed on the scan tool, check for trouble codes, observe applicable data streams and, if available, use the bi-directional feature to manually activate both low- and high-speed operating modes. But the most direct and accurate method for diagnosing any modern cooling fan system is to connect an enhanced-level scan tool. ![]() The easiest test for cooling fan function is to activate at least one fan by turning on the air conditioning (A/C) system. In other applications, the cooling fan speed is controlled by the PCM, which activates low- and high-speed fan circuit relays. On many modern import applications, a fan module that pulse-modulates the fan motor circuit controls the cooling fan speed. An overheat problem symptomatic with slow driving indicates that the cooling fans aren’t activating or aren’t running at full speed. Photo 2: The 2.5L Subaru engine is known for the cylinder head gaskets failing between 100,000 and 150,000 miles of service. ![]()
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