Help - 5.7 Coolant Drain Question

Quick question, I drained my coolant from the radiator to do a few things and noticed some time later that the overflow tank is still full. Isn't this supposed to empty when I drain the radiator via the petcock?

 

You empty the overflow with a pump or baster or undo the hose and let it drain down. There's also block drains on either side of engine.

 

Not necessary. If it happened so that petcock burped air bubble in, air will travel up the radiator and disrupt flow from the overflow tank.

 

Thanks, had me worried. Trying to diagnose an overheating issue that points to the fan clutch but the clutch seems fine, thought maybe it might be a clogged radiator for a minute

 

Check thermostat. If it stuck closed, you'll be overheating.

 

Putting a new one in just as routine, but it only overheats when idling for some reason, thought it should be the clutch but its plenty tight with no play. Haven't been able to observe the fan when running though (for complicated reasons). I think I'll fill with water so I can check the fan before I replace all the coolant.

 

Check the fuel trims, too. If the engine runs learn, it will be overheating. It can run lean even if the trims are good, that would be an old and tired upstream oxygen sensor(s). They are up for replacement every 100k miles in theory.

 

Check radiator cap. The rubber seal falls apart and creates clog. Fairly frequent issue.

 

Well that turned into a small fiasco. I pulled the old tstat out to find that some hack had used black FIPG on it previously. Took forever to clean it all up in that tiny space.