[Y-Blockhead]

Originally Posted by GPierce

The bypass valve bypasses the filter if it gets stopped up preventing oil starvation. It reacts to the pressure drop across the filter media not the oil pump delivery pressure.

https://www.pgfilters.com/tech-tips/...ve-oil-filter/

Originally Posted by alexiskai

It's both, really. Per your link:
The valve is designed to open when the oil filter becomes clogged or when the oil is too thick.

Bottom line, the bypass/relief valve opens in any situation where the filter media restricts the oil flow enough to create that 8 psi pressure differential.

Finding the psi rating of the bypass valve can be kind of a pain. It's published for some filters but not for others.

For example, here is the oilfilterdata.com page for the Wix 51515, which is a common choice to use with the valve cover oil filter setup. You can see the bypass valve on this unit starts to open at 8 psi, and then is fully open at 16 psi.

But other filters are different. The Purolator L30257 opens at 20 psi and the Wix 51355 opens at 33 psi. That might be above some folks' comfort level.

I think we agree on the BYPASS valve. But that has nothing to do with the Model A oil pump having enough pressure to pump oil thru the filter or the anti-drainback "valve" (what some to refer to as a check valve).

I think you would have to be pretty negligent on your oil changes to plug an oil filter.