Oil drain question

[gfh77665]

I pull my '97 Chevy Pickup up on the ramps. Slide under the V6 and remove drain plug, stream of oil shoots out vigorously, lands in pan about 12"-18" away, just like it normally does. Stream starts to slow, then I slide pan up directly under dain hole to let it drip a while.

After getting out from under the truck, I noticed I did not remove the fill cap or even the dipstick. Question: why did the oil drain quickly, with the same stream force as it normally does with fill cap and/or dipstick removed? I would have thought there would have been slight a bit of a vacuum, and oil would have burped out slowly. Any explanations for the "fast as always" drain even though the engine was still sealed?

 

[chubbs1]

I have done it both ways and I don't think it is a big deal, how warm was the oil? If it was pretty hot it will shoot out fast.

 

[ChrisD46]

I have drained both ways - with and without removing the oil fill cap and it seems to flow out strongly either way . I will remove the fill cap in the top of the engine (eventually) where I pour in another half a qrt. of Super Tech to clean out any left over dregs from the oil pan . I would say it's always best to remove the oil fill cap before draing the oil underneth - but it seems to work ok either way for me .

 

[willix]

The PCV system has a fresh air vent usually to the TB or air cleaner or somewhere in between.

 

[ltslimjim]

Yeah, and gravity is gravity.

Though, I do remove the oil filler cap and pull out the dipstick, in case some air tight pocket needs relief. Other than that, most of the oil comes out regardless of engine. Sometimes doing the extra helps on some vehicles. You may get an extra 'belch', if you will. Also, I leave the pan draining and remove the oil filter with the plug still off on the pan. I deliberately take my time and it turns into a 2 hour job max. I just like to see as much of the old crud leave as possible.

 

[gfh77665]

Originally Posted By: chubbs1
I have done it both ways and I don't think it is a big deal, how warm was the oil? If it was pretty hot it will shoot out fast.


Full temp. I had just driven 40 miles, and plug was pulled within 5 minuets of shutting engine off. I did remove the cap and dipstick five minuets later, but at that point only a dribble was still coming out. I feel the drain was real good regardless, since I let it drip for a half hour. Thank you all.

 

[mechtech2]

Like mentioned, the fast flow is provided by the vent for the PCV system [some sort of breather inlet].