Coolant Loss Over Time

Given the cooling system is a sealed system, can a small amount of coolant be lost over a period of time, merely being "used up"?
I have noticed the level in the radiator overflow tank changes with altitude.

 

Because my truck is a 2005, I monitor the cooling system very closely. I don't believe I'm losing coolant but was curious if any of it is lost in regular use over time.

 

Based on direct observation through the many vehicles I've owned/driven over 35 years ... no, coolant does not burn away or get absorbed. If you start losing coolant it's gonna be due to a leak somewhere in the system - that includes head gasket failure, heater core, radiator, water pump, hoses, ruptured radiator-transmission fluid reservoir, etc...

 

The radiator/overflow tank hose has minimal seepage where it connects to the tank. Never seen any moisture, just a little white powdery residue. Perhaps on continous exposure to the air, a small amount of coolant is evaporating or oxidizing and leaving the residue.

 

Yep...evaporation. I lose about an oz. or two in between oil changes.

 

I had a similar problem with slow loss of coolant in my 1994 4 cylinder pickup. It also had a slight rattling noise from the front of the engine, only at idle. I had 2 mechanics check the noise and misdiagnosis it. At almost 200,000 miles, at 70mph on a Sunday night the rattling intensified abruptly, the check engine light came on and the temp needle pegged on H. I had no coolant. The mechanic who did the teardown said the cam chain tensioner had worn out and the chain was loose and gradually wore a hole into a coolant passage. So, you might want to put that on a list of things to check>

 

One simple thing to eliminate first is to buy a new radiator cap. When they get old, they can lose their ability to hold pressure.
Put a new cap on it and keep an eye on it. Rule out the simplest first.

 

Good idea. I should have changed it when I drained and replaced the coolant not long ago.

The only thing I am really worried about is the known issue with the 2005 head gaskets.