I changed the oil for the 2nd time last week and I noticed I didn't have any oil in the 5 qt jug. I had mistakenly poured the whole 5 quarts back during the 1st oil change at 10K+. The MPG seemed the same throughout the 10K+ to 20K+ with 5 quarts. This time though, I poured the prescribed 4 quarts into the engine. But now I'm wondering if I should pour in the 5th quart now since another quart would keep the oil cleaner until the next oil change at 30K+ miles. So the question for is, will having 5 quarts in the crankcase adversely effect anything?

 

Yes. Too much oil and it starts to foam, and foam doesn't lubricate well. You might have gotten away with it because it's a relatively new engine with little wear.

 

Please google this topic and see in general what happens when you overfill a car with oil. Sounds like you got lucky the first time, dont make the same mistake again... You would hate to incur out of pocket repair costs too (no warranty likely if you overfilled your crankcase)...

 

How about summarizing for us what you gathered from searching google?

 

Sure! At a high level, overfilling the oil is bad... Amazing, huh?

 

From your google search, at what point of overfilling would damage occur?

 

From page 367 of the Owner's Manual:

9. Pour the recommended engine oil into the engine.
Engine oil change capacity (including filter):
3.5 US qt (3.3 L)

IOW, you're overfilled now. The crankshaft whips the oil into foam, which doesn't lubricate well. You may've put 50,000 miles or more wear on the motor in the last 10,000 miles.

 

Engineers leave a certain amount of latitude for error and it's fairly common to design for overfill to 5 quarts since that is what Earl, the oil guy at Armpit Flats Chevrolet, will put into every car he services.

On the other end of the spectrum, as long as the pump is supplied with a constant stream of oil without air the engine will not suffer unduly.

This isn't to say you shouldn't stay within specs, but if you happen to be a bit above or below the lines on the dipstick it doesn't mean disaster at the next engine revolution.

 

In the middle of nowhere. At night. In the rain.

There are markings on your dipstick. Use them.

 

Overfilling can cause seals blowing out and oil leaking thereafter.
Wonder what led the OP to pour in 5 qts???

 

The OP stated it was a mistake.