mga bossing, need help.

i'm getting an elf isuzu truck either 4bc2, 4be1, or 4hf1 engine. nagpunta na ako sa mga surplus trucks dealers and direct importers but haven't decided yet. i want to make sure that I get the best engine condition yung hindi blow by (of course) or about to blow by in a few months or so. how to check the engine? wala kasi akong maisamang mekaniko so I need tips on how to check. meron nga akong tiningnan medyo may usok (itim) peros sabi nung mekaniko ay hindi pa daw kc nachange oil. from japan pa daw ung unit. okay na man tunog nung engine. meron din akong tiningnan na 4hf1 engine dami talsik na oil sa oil cap at dip stick kapag pinaandar makina. sabi nung mekaniko normal daw sa 4hf1 dahil ohc engine type daw cya unlike sa 4be1 and 4bc2. hehehe... tulong naman mga bossing experts on diesel engine.