Why does antifreeze overflow from the reservoir?
2 Answers
Antifreeze may overflow from the reservoir for the following reasons: 1. Damaged reservoir cap: Check if the reservoir cap is damaged. When the temperature inside the reservoir is high, antifreeze will leak out if the cap is damaged. 2. Overfilled antifreeze: If the antifreeze level exceeds the marked line on the reservoir, it may overflow during driving. No overflow will occur when the antifreeze level is appropriate. 3. Thermostat malfunction: A faulty thermostat can cause the engine temperature to rise too high. When the coolant cannot enter the engine water passages for major circulation due to high temperature, the antifreeze will undergo minor circulation in the radiator, leading to overflow.
The other day while driving, I noticed antifreeze overflowing from the reservoir, leaving green liquid all over under the hood. I immediately turned off the engine to check and found the main issue was excessive pressure in the cooling system. It might be due to a faulty radiator cap that failed to regulate pressure properly, causing the fluid to expand and spill out when hot. Another common cause is engine overheating, such as when the fan isn't working or the thermostat is stuck, leading to high temperatures and expansion overflow. Once, I carelessly added too much antifreeze, exceeding the MAX line, and it seeped out when parked. If this happens frequently, be cautious about internal issues like a leaking head gasket allowing exhaust gases into the system, which spikes the pressure. It's advisable to check the fluid level after the car cools down—if it's too high, remove some. Replace the cap or inspect the hoses for blockages and leaks. Don't ignore it; fixing it early saves big trouble and won't cost much. Regular maintenance should include monitoring fluid levels and system seals—safety first.
