Hi, the original correct capacity for a Cat 3126 with shallow pan (stamped steel) is 22 quarts but that may cause blowby. Cat reduced the 22 to 19 as acceptable .... generally, 22 is fine if not blowing any oil out the breather ... try 20 if it's blowing oil ... Cat seems to think anywhere between 19 and 22 is OK. My old 3126 was most happy at 20 quarts and that's where I marked the stick. I suspect your guy did NOT add 3 gallons .... maybe 3 QUARTS. BTW, the reason Cat tried 22 (from 19) was to obtain a longer change interval. Didn't work well on all engines so they came up with the 19-22 range.
