well i have 278600 on mine, oil pump went out on it finally, ive used 530 1030 and 1040, doesnt seem to make a dif, but if its cold outside always use the 5 20 or 30 whichever yours calls for mine calls for 530, the lower number is startup viscosity, after that it warms up to the thinner 30 weight viscosity, the 40 weight i found actually caused a loss in oil pressure on my guage, so i went back to the thicker 530, then i couldnt get 530 in castrol gtx like i use (dad always put pennzoil in it and i didnt like the way it looked when i drained it) so i got the 1030, it was summer and it didnt drag the starter but when we got a good ole louisiana cold snap i noticed it was a lil slower starting even tho i had a good hot battery. my advice always stick to the oe viscosity. if your running a synthetic stay that way, if your running mineral oil and are thinking of going synthetic dont go mineral then syn youll have seal trouble, go mineral to semisyn or blend as its sometimes called and check seals, if no problems go full syn. i didnt see any dif performance between reg oil and high mileage oil and even had a manufacturer tech tell us its the same stuff dif bottle b4 if you have a question about that too. just stay away from quaker state as it was designed yrs ago to gunk up to protect aluminum blocks and still does which is never good for the oil pump!