I mean that just about every engine has an oil pump inside it, otherwise there would be nothing to create oil pressure to pump the oil around the engine. To fit an oil cooler you need to tap in to a place with high oil pressure and a place with low oil pressure. I don't know much about your engine but assuming that the strainer works in the same way that my engine's filter works you could block off the return hole where the strainer is, get oil from the strainer compartment and return it via the oil filler hole by drilling and tapping holes in the oil filler cap and oil strainer cap and attaching hoses to them. This is just guess work by the way, don't start drilling holes in your engine based on what I just said ;)