Overheating: Why does my Subaru over heat sometimes and no others????????
Well there are a number of possible reasons for overheating. Basic service should include a visual check of the overflow bottle of your cooling system. This plastic bottle on the side of your radiator holds the overflow coolant. There are 2 lines on this bottle a high and low line the fluid should be in between these lines. The coolant should be free of any oily gunky material. Coolant today comes in various colors, yellow, blue and green. The color is not as important as the contamination of the fluid and bottle. There should not be any residue either on the fluid or on the sides of the bottle.
Now to the what’s and whys of overheating. We have checked the coolant overflow bottle and the coolant is at the proper level and it is not gunky in the bottle. As you are driving you notice the temperature gauge heading to the top. Stop driving pull over and have the car towed to a service facility, continued driving can cause you to ruin the motor beyond repair!!!!!! You can test your electric fans by opening the hood starting the motor and listen for the electric fans, to make sure these are running. During regular operation the fan should cycle off and on. Now you notice there are 2 electric fans mounted on the motor side of your radiator. As a rule the one on the driver’s side is for engine cooling, the one on the passenger’s side of the car is for extra cooling while the a/c system is in operation. These fans are controlled by sending units installed into the cooling system turning the fans on and off with coolant temperature.
There are other reasons for your Subaru to overheat, some simple and some more complex. The radiator over time can become restricted internally and slow down the flow of coolant causing the motor to run hotter. If you have not replaced your radiator hoses during regular services you may have a collapsed hose restricting flow. Hose manufacturers recommend cooling hoses be replaced from 18-24 months depending on driving habits. There is always the possibility of a thermostat failure, this usually causes an irregular overheating pattern, sometimes sticking closed and not allowing any coolant flow and pegging the temp gauge.
The Subaru water pump is rarely the cause of overheating. This pump is operated by the smooth side of the timing belt and is under constant side load due to the belt routing. This style of pump is well designed and hardly ever fails to pump coolant. The pump will leak and loose its ability to keep the cooling system pressurized but as a general rule will not stop circulating coolant. That said I never say never, it’s a man made mechanical device and can always fail, but it is very rare.
The radiator cap is often over looked and can be an overheating problem. We replace the radiator cap during our scheduled services as it is a wear and tear part. If not replaced on a regular basis it can become weak and ineffective and allow coolant to push out of the sealed system. The coolant will fall below Subaru’s accepted minimums and allow the motor to overheat. We also see some of the quickie low priced oil change guys selling you a radiator cap as they tell you yours has failed. That is a distinct possibility, but what they sell is a universal fit all cap not specifically designed for your Subaru. These fit all caps may not be rated at the correct operating pressures for your Subaru and may cause loss of coolant and add to your overheating problems. We ONLY use genuine Subaru radiator caps engineered and designed for your Subaru.
Now we have worked down through the least expensive overheating issues. There are some more expensive possibilities for overheating, head gaskets. Head gaskets are another wear and tear part of your Subaru motor. When a head gasket fails it can allow internal compression to transfer from the cylinders to the cooling system. Cooling system pressures run between 7-16 pounds. Compression can run to 150 pounds. If this higher presser transfers to the cooling system the water pump cannot circulate the coolant and the motor will over heat. This usually will leave a slimy oily film in the overflow bottle. At times this added pressure will actually blow a hose off the radiator or heater core
