The Inside of an 80 Series Oil Filter

People often wonder what goes into the factory oil filter for an 80 Series Petrol motor. There are a number of structures in there that do more than just filter.

For one, there is an anti drain back valve which assists in keeping the filter and oil galleries higher than the oil filter full of oil. This greatly assists in ensuring vital lubricating oil is available quickly at start up. Otherwise a good deal of wear would occur at start up whilst waiting for oil to be pumped from the sump, fill the oil filter and finally get up to where it's needed most.

Another structure is the filter by-pass. The filter medium is restrictive to flow. As the filter becomes clogged, or if high viscosity oil is used in cooler climates, it becomes difficult to pump the required volume of oil through the filter. In order to ensure adequate oil flow, the filter medium itself is by-passed when the resistance is high. It may come as a surprise to some that this type of filter is not a full flow filter (fuel filters are). At higher engine speeds and with high volume of flow, most of the oil by-passes the filter medium.

Many thanks to Norm of Traction4 for the following words and pictures.

Shows anti drain back. The outer edge of the red membrane seals against the top of the filter. It is forced aside by oil pressure when the engine starts and oil enters via the small holes.

Shows the belville type spring that makes the whole filter medium cartridge into the by-pass valve at high oil flow rates. High flow causes the spring to compress, forcing the whole cartridge down and allowing oil to flow past the inner edge of the red membrane.

Shows the primary by-pass valve (at the closed end of the filter under the belville spring) that will be forced open by oil pressure if the filter medium is blocked.