Im about to change the oil in my new 383 for the 2nd time (1st was after cam break in), and I was wondering about a couple of things. Ive heard numerous times that you shouldnt run synthetic until after the first 500 miles. is this true for all motors or what? Mine is not a daily driver, so it will be a while before it ever has 500 miles on it. I was just wondering if I can go ahead and switch to Mobil1 or if I need to wait (motor has maybe 80 miles on it, I wanna change it because its lookin kina dark).

2nd, what is oil weight based on for each motor? I mean if you have stock tolerances with a hi-volume oil pump can you still use 10w-30? Im already regretting putting the hi-flow in since I still have the stock pan, so for now Ill have to deal with it. Anyone have any problems with using a hi-volume pump with stock tolerances? But either way I was just curious as to what its all based on.

 

1) It is said not to use synthetic during breaking due to parts not actually being able to break in (less initial wear) If the motor has had a few hours run time (being the 3rd change i would assume so) Their should be no problem going synthetic now.

2) Yes oil weight selection depends on what size bearing clearances it has to 'fill', i would say stick with 10w30.

 

i know that synthetic oil will not let the rings seat properly to the cylinder walls. as far as the tolerances that's a little out of my league

 

If you want to know whether the rings are ready for synthetic oil, do a leak-down test.

If the shop that did the final cylinder honing had any clue about what they were doing, the rings are most likely seated by now.

Any clue what the final bearing clearances were? If they were loose, use xW-40. If tight, use xW-30.

 

I cant remember the tolerances off hand, but I know they were close to factory specs.

BTW: would a compression test show the same as a leak down test? I remember that just about every guy in my shop's got a compression tester, but they all look at me funny when I ask for a leak down tester.

 

A compression test might help a little if you know what the compression pressures were before you fired it up.

You can get a leak-down kit from Harbor Freight.