Oversize filter and MDS

[detroit54]

I hate to dredge up an old topic, but...

I've read about the benefits of oversized filters and would like to use one. I have a 2005 Dodge Magnum with the 5.7L Hemi with the multi-displacement system. From what I've read, this MDS relies pretty heavily on the oil system (anything heavier than 5w20 and the system won't work) so I don't want to do anything that could cause a problem.

From Popular Mechanics ( MDS article ), the MDS is supposed to be active between 18 and 75 psi. If overall oil pressure were to drop due to a free-flowing filter, the MDS might engage for longer and help gas mileage a bit, although I doubt a better filter would be worth more than 1-2 psi.

Should I expect the oil pressure to drop after installing an oversized filter? Does anyone know if using an oversized filter is a bad idea with MDS? Or should I just assume that Chrysler designed this engine to use a PH16 equivalent for a reason and stick with a short filter due to lack of info?

 

[slalom44]

Since oil pumps are positive displacement, you get essentially the same flow regardless of flow restriction through the filter. If the media was less restrictive (assuming this is the case with an oversized filter), this could reduce the oil pressure upstream from (before) the filter but it won't change the pressure seen downstream from (after)the filter.

You might want to read another thread on this forum started by Gary Allan. He has rigged up his car with oil pressure gauges before and after the filter. His experiment has shown this to be true.

 

[labman]

About oil flow and pressure. The volume coming out of the oil pump may not vary with the viscosity, but the volume going to the engine will be reduced at high pressures by what goes out the pressure relief valve. No matter how big or small the filter, the pressure drop will be limited by the filter bypass. The total flow will only drop slightly on a more restrictive filter. A better flowing filter, with the same bypass, just flows more of the oil through the media. If it shows less pressure before the filter, it will have more pressure after the filter.

So a bigger filter should give you cleaner oil, especially later in an OCI. Watch your clearances and don't fall for a big empty orange can.