Overheating: Why does my Subaru over heat sometimes and not at other times????

There are a number of possible reasons for overheating. Basic service should start with a visual check of the overflow bottle of your cooling system. This plastic bottle on the side of your radiator with a yellow cap holds the overflow coolant. There are 2 lines on this bottle a high and low line about 1/2 way down, the fluid should be in between these lines. The coolant should be free of any oily gunky material or heavy smell. 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. Next check the level of coolant in your radiator. NEVER NEVER remove the radiator cap when the motor is hot or the motor is running. Always wait until the motor has cooled. Once the radiator cap is removed the coolant should be visible in the radiator top tank.

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 check your electric fans by opening the hood starting the motor and listen for the electric fans to make sure these are cycling. 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. The a/c cooling fan is controlled by a sending unit in the a/c system. When you engage the a/c the fan will turn on.

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 an internally 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 part of the overheating problem. We always replace the radiator cap during our scheduled services as it is a wear and tear part working under high temperatures and high pressure.. 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 these low priced oil change guys selling you a low quality 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 use only 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, the dreaded 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 up to 150 pounds. If this higher pressure transfers to the cooling system the water pump cannot circulate the coolant and the motor will over heat. This condition usually leaves a slimy oily film in the overflow bottle. At times this added pressure can actually blow a hose off the radiator or heater core. If you continue to drive your Subaru with “blown” headgaskets, you risk very expensive damage to your cylinder heads and possibly the motor. This is a very serious issue and needs to be addressed quicky. The sooner you resolve the overheating problem the less it will cost you in the long run.