Originally Posted By: SteveSRT8
Facts. Relevant only to GMC fleet ownership.
All our 3500 Savanas have 3/8 inch oil cooler lines running above the filter mount. A ton of oil is in these.
Even after sitting for DAYS, if you remove the filter (with no ADBV) those lines will flow oil for many seconds and then drip for hours.
All the theorizing here is just wacky, there is no way a low mounted vertical thread filter is going to allow all the oil to drain back into a sump. It can only siphon if it is higher than the place it drains to.
Doesn't happen on 4.8/5.3/6.0 GM motors.
Who here has a vertically mounted filter threads up that drains itself dry when sitting? Anyone?
My Toyota suedo lawn mower engine in the Prius holds the oil over the vertical, low mounted, threads up, filter for at least 12-24 hours, as that is how long I drain the oil most of the time now. Lots of oil in the passages above the filter comes out when filter is taken off. There is just surface tension and the adbv to hold the oil above the filter. On The GM engines without filter adbv, I suspect there is a check valve between the oil pump and filter inlet, same effect as the filter adbv. I saw this described in an old auto mechanics book, not theory, not made up in an armchair. They described the two types, in filter, and in engine. They knew the dangers of dry running while the oil lines/filter fill up as well 50 years ago as we do now. From my armchair, without GM engine drawings, I bet there is a check valve holding the oil from returning to the pan.
