1999 Volvo Penta "WT" Models Workshop Manual, Page 281Get this manual
Normally, all engine oil passes from the block through an OEM filter adapter If the remote oil filter or lines become restricted, spring loaded bypass valve opens in the adaptor and circulates oil back into the blockInspect bypass valve spring and valve disc for proper operation or damageIf replacement of bypass valve is necessary, remove bolts and adaptorClean valve chamber in block and replace adaptor
Oil Pan _
Removal
1Remove timing chain coverSee Timing Chain, Cover and Seal in this section2Remove oil dipstick and withdraw oil using suction pump3Remove oil dipstick tubeRemove screws, oil pan and gasket4Remove oil dipstick tube fitting from oil pan
Installation
1Thoroughly clean all gasket sealing surfaces