Coolant leak - coolant level steady

[vavavroom]

Vehicle loses maybe an ounce of coolant overnight from a leaky water pump. I caught the drippings and it is definitely coolant. The coolant level in the expansion tank has remained the same for a week. Should I call Mythbusters?

 

[TheLawnRanger]

Slight overfill?

 

[Rhymingmechanic]

Is the pressure cap on the expansion tank or the radiator? If it's on the radiator, check the level there. A leak could be preventing suction from the "overflow" style tank.

 

[vavavroom]

It's not overfilled. The coolant level cold is right between min and max marks on the expansion tank. The pressure cap is on the expansion tank. Coolant operating temperature is normal, heater works, so hopefully no huge air pocket.

 

[Lyman]

Expansion tanks don't always work when you have a leak. A leak takes away from the vacuum needed to pull the coolant back into the radiator.

 

[andyd]

Does the radiator have a cap? Open it when cold to get a better idea.

 

[maxdustington]

My car is leaking coolant, and it went a really long time between fillups. At least a few months, it was mostly short trips though so that may have had something to do with it. It went from needing a top off every few weeks to lasting from last autumn until a few weeks ago

It went so long I thought it had repaired itself.