BellePlaine wrote:So you are saying that thicker oil requires more filter surface area then thiner oil. Makes sense. Does this mean that the target oil pressure at the filter should remain constant?
Yeah, thicker oil needs quite a bit of "paper" (although it's not really paper exactly) to let a good flow through at any given temperature. Of course, as the oil warms up, it gets easier to pass. And there is always a pressure operated bypass valve in the vehicle's oiling system or the filter depending on the filter model and vehicle to let some oil go around the filter media when it is cold and thickest, or at higher than normal engine RPM when the oil pump is really spinning. This prevents oil starvation downstream from the filter.
For example, my truck and Bus both need a filter with a bypass built in, because the truck (like most) does not have a bypass valve built into its oiling system, and my Bus has an aftermarket oil filter set-up as it is an early Bay with no original filter.
Late Bays, I'm told, (and many GM engines) have a bypass built in to the oiling system, but can also use a filter with one in it with no ill effect.
As for the second part of the question, the pressure at the filter will always vary with oil viscosity, temperature, and RPM, but cannot be allowed to exceed the pressure limit of the filter. That's what happened to me.
The ACVW engine regulates system oil pressure maximum (not the same as the filter bypass thing) downstream from the filter. Most engines (modernish) do it upstream at or near the pump.
My oil pressure was OK downstream from the filter, but upstream, the cold, thick oil was pressing hard between the outside of the "paper" media and the metal canister. My gauge doesn't read that area.
That spring loaded bypass valve inside the PH16 I was using was probably fully open trying to let oil get by the media, but it wasn't enough, and I blew the gasket out of the filter. My OP warning light came on, and I shut it down to find a stream of oil on the ground behind me.
I wonder if it would have happened if I had been using a "better" filter with more media?
Anyway, I think the Fram here was kind of a rip-off for the size. Hardly any guts in there compared to the Purolator which only cost about $1 more. Buyer beware.