[Huskymaniac]

Here are the results based on some data and some estimates gathered from the service manual and oil filter data. The oil assumed was a generic, but high quality, 5W30 oil. The filter assumed was an oversized Purolator P1 or equivalent. Pressure and flow were calculated for 0C and 80C oil temperatures. Three different bypass pressures were used for the oil filter.

In the first plot you have the oil pressure (filter plus engine) and oil flow at 80C. The oil pressure never exceeds the maximum pump pressure so the flow shown is full flow as specified for our oil pump. Since the filter differential pressure never exceeds even the lowest bypass pressure, there is only one curve for pressure and flow. The second plot shows what happens at 0C. Notice that the pressure is above the maximum pump pressure at all RPMs, regardless of bypass pressure. The result is a greatly reduced flow which is well below the design flow rate for the pump. Compare to the first plot. Also, the filters do go into bypass at 0C. The only difference is at what RPMs they go into bypass. The result is that the filter which bypasses at a lower pressure will result in a higher flow rate. But you can see how minor that impact is. It is much less important than the oil temperature. The last plot compares oil flow for 0C and 80C. I had to use a log scale to even make it look reasonable. Each horizontal grid line represents a 10X increase in flow rate. Clearly the engine is starved for oil at low temperatures! I am going to re-do this for a 0W40 oil I am toying with using.