Coolant in reservoir keeps dropping below the…

[Cory]

Hello,

One day I went to check my engine oil and noticed that my coolant reservoir tank was way below the “low” mark! The radiator was still full. This was on a cold engine that sat overnight, and the supply hosed (hose that goes from the radiator into the tank) was still submerged into the coolant.

I don’t know if I should be concerned; coolant keeps disappearing in the reservoir and I see no apparent leaks. The hoses still look really good. The radiator is always full. Coolant mixture looks blue (Honda coolant in use) and the oil/crankcase fill cap doesn’t have any junk on it.

maybe I’m being paranoid.

2005 Accord 4-cylinder – 150,000 miles
always drank Honda coolant

Is dropping levels in the overflow tank normal?

Topic

[dreamer2355]

If the reservoir is constantly empty, the coolant is going somewhere.

Here is Eric’s overheat video. It will show you steps you can also use for your scenario, particularly the block test and cooling system pressure test 🙂

[spelunkerd]

Coolant is going somewhere, even if you don’t see any leak. I would run the vehicle in one spot for a half hour and inspect really closely for leaks, especially where coolant and heater hoses enter and leave the engine block, and underneath the water pump. Tiny leaks of hot coolant near the engine block can evaporate away, leaving a discolored crystal residue. And, leakage usually happens when the system is under pressure, so you won’t necessarily see anything on the ground after turning the engine off. Sometimes a coolant drip will pool over structures underneath and then evaporate away without ever hitting the ground. Also, have a look at the carpet inside the cab to look for leakage that might come from a leaking heater core.

If you don’t find anything with that effort, you could pressure test the system, and then after that I would burp the system to be sure that air wasn’t introduced into the system when coolant level fell too low at one point. Air in the system can cause overheating, causing more air. Break the cycle by burping and keeping level topped up well above the minimum fill point.

[EricTheCarGuy]

It’s normal. 50% of coolant is water. As the water gets hot it turns to steam and goes into the atmosphere. Over time coolant levels will get low because of this action. This has more of an effect in warmer weather.

[Author]

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