10w20 is to thin if thats what you have in it. try some 20w50 the car is old enough and the tolerances are larger it can handle it. just dont try this on some new import.
the first number when choosing oil dont mean shit unless your in a cold enviroment. and the higher the number the thicker the oil.
i pesonally use amsoil 5w-30 in the camaro. 5w-20 in the dailly beater and shw sae 60w in the drag toy (basically rear gear oil)