I noticed recently the coolant reservoir was nearly empty in my 2008 Civic. Checked radiator, and could just see the coolant at the bottom of the neck, which I understand to be normal. Temp gauge reading normal. Thought I had a possible leak, so I added some coolant to the reservoir last night and …

The radiator cap controls coolant leaving and returning to the reservoir. Try replacing the cap. Tester

Interesting, ok. A bad radiator cap would mean loss of pressure, which would lead to the car wanting to pull all the coolant into the radiator?

The pressure cap is on the expansion tank. If the cap is weak, it can allow coolant to escape as a vapor. Tester

The radiator should bee completely full, reservoir is usually around half. There normally marks on the reservoir indicating cold and hot levels. Follow Testor’s advice, replace the pressure cap, add the appropriate coolant to the reservoir to the “cold” mark. Then drive the car. Level should sta…

Ok. I think I may have just been low on coolant then. I think I misunderstood what a “full radiator” meant - I didn’t realize it meant that the fluid should be near the top. I actually pulled my reservoir out and there was fluid in there actually just below the min level. It was just hard to see be…

If coolant recently replaced and full, entrapped air can eventually work its way out as you drive, which will cause coolant level to drop in expansion tank. As long as radiator is full, there’s no immediate coolant emergency. After about 100 miles of driving any entrapped out has had a chance t…

If the radiator is not full coolant will not flow back to the res but simply stay in the radiator. Fill the radiator and res and try again. Leaks in res are not unheard of either.

Also make sure the heater is set on Hot. That opens the valve between the engine and the heater core so coolant is making a complete circuit. That can help expel air that might be in there, as well as assure the whole system is filled with coolant. Top up the radiator and reservoir after a complete…

Radiator FULL, but reservoir nearly EMPTY after adding coolant

Maintenance/Repairs

Cavell December 13, 2022, 2:00am 10

Does reservoir have fill line? If so, fill it to that line.

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Radiator FULL, but reservoir nearly EMPTY after adding coolant

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