Oil filter level

[Toolguy]

(07-30-2021 )JimT Wrote:  So, this may be an odd question. Dr. Google suggests it's fairly normal, but I'd like a second opinion.

Changed my oil tonight. Got home, shut the truck down, went and ate dinner. About an hour later I came out and drained the oil. When it's hot it drains so fast that it nearly overflows my catch pan so I purposefully don't open the oil cap or dipstick to let any extra air in. Once it was empty I went and spun off the oil filter to find it no more then half full! Every other time it's been so full I spill a little as I tip it to get it out. Not this time.

Google search suggests this is common, if you let it sit for a while after shutdown some oil will syphon out... It's a first for me. Any thoughts?

Oil pressure has been normal, maybe 1 psi +/- at most. Oil darkened up a little faster than normal this time around, but fuel mileage has been a little lower due to operator abuse ;) Overall still no darker than normal oil changes, smelled normal, about 14,000 miles.

Possible vacuum draw, from the hot oil draining fast and not letting air into the block?