Does the radiator need to be … read more May have dropped 1/2inch over the last 3 months when the engine is hot. Engine coolant is vital to your vehicle's function. How to Check Engine Coolant Level. Honda Civic 2003, 112k miles. The coolant is meant to absorb high temperatures from the engine and as such your radiator is going to be under pressure and the fluid inside will be extremely hot. Hot coolant expands into the overflow reservoir, and some vapor may escape. Never refill your coolant when your engine is hot. Engine overheats occassionally and heater takes time to supply hot air, and gives cold air when car is overheating. If you were to open the cap when the engine is still hot, you're going to suffer some serious burns as a result. I assume you are referring only to the Low-Coolant warning light and not the coolant reservoir under the hood. Always check coolant levels in a cold engine. If you open a radiator cap when the engine is still hot, you could be burnt by escaping steam or hot coolant. Yes. I would have suggested using a Block Test to check it (with blue fluid turning to yellow indicating gas in coolant) but as the first post says, this has been checked already. Always wait for it to cool down. Not only does it keep your engine cool and protect it from overheating, which can cause a number of detrimental and costly problems, but also allows your engine to function at its optimal level. Even after opening the cap, pouring cold or room-temperature coolant into your hot system could crack a hot engine block. Another symptom of a problem with the coolant temperature sensor is an overheating engine. Finally, the coolant level on my 2006 Sienna, 1993 Caprice, and 1995 Dakota does not drop between changes (~3 years). The coolant level drops when the engine get hot (coolant level low warning comes on), it seems to fluctuate and the warning light goes on/off during a trip. Last week, when I got back from a trip (45 min), the level was below the tank, then the next morning it was back to around the min mark. The coolant level should be at the tank's MAX or HOT line when the engine is hot, and lower when it's cold. The coolant temperature sensor can also fail in a manner that causes it to send a permanently hot … I would have the oil checked for any coolant contamination, it might not hurt to replace the radiator cap if it’s not holding pressure. High engine compartment temps. 3.2. Coolant level is at Max. Draining out the coolant and refilling the system removes dirt and rust particles that can clog up the cooling system and cause problems in winter and summer. 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