What Is This Hole In Oil Filler?

[Fly Boomer]

This is what my oil fill looks like (TSIO-520) with the dip stick out:

 

What is the hole near the bottom that isn't the dip stick hole?

 

[jetdriven]

whats with all that rust

 

[PeteMc]

4 hours ago, jetdriven said:

whats with all that rust

As I understand it, it comes from the moisture and slightly acidic oil (as you put hours on after the oil change) that comes out of the engine.  Also from the ambient heating and cooling of the engine as it sits on the ground.  In most places there is always some humidity that makes its way into the engine and the tanks...  Which is also why they always say to have full tanks to keep the air out and cut down on the condensation.  

Is the top of your oil cap not rusted at all?  New plane or new cap?

 

[RLCarter]

My guess is any oil that gets in the filler neck that is not blown out the breather drains back to the sump through that hole

[carusoam]

Water likes to condense on the metal filler cap…

Indoors, some people loosen the cap to allow steam to escape…

The pic looks a bit more like cooked oil collecting on the surface…(?)

PP thoughts only, 

-a-

[RLCarter]

25 minutes ago, carusoam said:

………The pic looks a bit more like cooked oil collecting on the surface…(?)

Thats what I think as well

 

[carusoam]

Interesting that the dip stick scratches through all the build-up…

Best regards,

-a-

[Hank]

2 hours ago, carusoam said:

Interesting that the dip stick scratches through all the build-up…

That comfir,s to me that's its old, cooked oil and not rust.

[buddy]

To solve the condensation problem just pull the dip stick out a few inches after each flight until the engine cools down a bit, that should solve a moisture problem.

[PeteMc]

6 hours ago, buddy said:

To solve the condensation problem just pull the dip stick out a few inches after each flight until the engine cools down a bit

In the winter when I don't fly as much, when we go to lunch I'll pull the Oil Filler Cap and lay it on the cowl and fold over the oil door to keep things from getting blown into the filler neck.  You see a lot of moisture coming out if the planes been sitting for a while and has boil it all out of the oil during the flight.

 

[Rjfanjet]

22 hours ago, buddy said:

To solve the condensation problem just pull the dip stick out a few inches after each flight until the engine cools down a bit, that should solve a moisture problem.

I've been doing this for over 30 years. Don't know when CFI's quit teaching this technique.