The engine on your Subaru Impreza generates significant heat when in use. To prevent it from overheating and suffering damage, the coolant system pumps a mixture of water and antifreeze through the radiator and around the engine to cool it. Check the coolant regularly to make sure that the levels are high enough, and that it contains the right percentage of water and antifreeze. It should contain a 50/50 mix, ideal to prevent freezing in winter and boiling in summer.
Open the bonnet. Locate the black metal radiator (just behind the front grill) and the translucent plastic coolant reservoir just to the right of it. Open the plastic cap on the coolant reservoir and check the fluid level, which should be at the line marked "Full."
Remove the radiator cap. Insert the tube of an antifreeze tester in the radiator and squeeze the bulb to draw coolant into the tester's chamber. Read the results using the manufacturer's instructions, which will vary between testers.
Add a mixture of 50 per cent distilled water and 50 per cent antifreeze with an anti-rust agent to the reservoir if the level is below the full mark and the antifreeze levels test as normal. Add straight antifreeze if the antifreeze levels test low; add distilled water if the antifreeze level tests high. Start the engine and run it for a few minutes, then allow it to cool and use the antifreeze tester again to confirm that the antifreeze level is correct.
Drain coolant from the radiator if the system is full, but the antifreeze tester indicates the mixture is off. Raise the vehicle and support it on jack stands, then place a large container under the drain tube attached to the bottom of the radiator. Loosen the wing nut on the bottom corner of the radiator with a pair of pliers to open the drain plug.
Tighten the wing nut to close the drain plug when the coolant has drained out. Pour the drained coolant into a resealable plastic container and clean up any spills, then dispose of it as household hazardous waste. Fill the radiator slowly with a mixture of 50 per cent water and 50 per cent antifreeze.
Fill the coolant reservoir to the "Full" mark. Run the engine for a few minutes, turn it off and allow it to cool. Check the coolant level and add more coolant to the reservoir if necessary. Repeat, adding more coolant as needed, until the level remains at the "Full" mark.
Ethylene glycol-based antifreeze is highly poisonous and its sweet smell and taste may induce pets to consume it, often with fatal results. Propylene glycol is much less toxic.
Never work on the coolant system when the engine is hot. The coolant will be under pressure and may cause serious steam burns. Wait at least 20 minutes after turning off the engine.