a half moon pin fell off the cooling oil line going to raditior,all the oil came

What is your question?

out replace pin,add oil,the van never ran good again,loud knocking noise but not all the time,oil gage goes down when brakes are applied,up when gas is applied.sometimes it dosent make noise at all.do you think i should put in 10w-50 check gages light flickers when brakes are applied and oil needle goes down.ty