I agree with Tom that if the critter has a filter, use detergent oil, if no filter, use non detergent. The multivis oils were to give "more constant viscosity" over a greater range of temps. Multi viscosity oils are sort of misnamed as they're not really multi viscosity oils at all but exhibit similar characteristics at low and high temps as their wts designate. 5W-30 means it exhibits characteristics of "5" wt oil in winter and "30" wt in summer( about 100 degrees C)

You guys are correct, I sometimes confuse myself with my own ramblings. Straight weight does not mean non-detergent. As long as a detergent oil is used everything is okay. It just makes things a little stiff when the temp gets cold.

They change the designations of oils at times but when I was dealing with Cats for years the oil used in the engines was Series-3 #30 in your case. Today I don,t know what the name or type is for it & there also was #10 Series-3 oil back then too for cold weather or whatever. Today you hear of the 15-40 oil being used instead of the single grade now.