Suprised you switched to syn so early. I would have ran dino for at least 2K miles. Seems like a hell of a lot of oil consumption
initially but I see it's calmed down now which is good. I'm almost suprised the plugs didn't initially foul
Per writings by a number of automotive and lubricant engineers, all suggest the requirement of break in of a motor on dino oil is a myth. The synthetic is not too slippery, per Shell's and Mobil 1 engineers. Notwithstanding, I understood, the preparation of the wet cylinder liners with the piston rings only requires a few hundred miles at most. Some writings suggest, it is accomplished more quickly than that. I think I ran closer to 300 miles before changing to Rotella. And I picked Rotella because of its parafin derived synthetic base, thinking this would be a good break-in synthetic.
The motor was initially set up with a pretty rich idle, and I did foul the first set of plugs by about 1500 km. These were Lodge 2HL plugs. I then went to NAPA and picked up NGK 6 and 7 ES, Autolite, and Champion plugs. At the same time, I adjusted the idle richness, and have been watching the plugs coloration, periodically.
I ran the Autolites briefly, while I ran some Techron through a tankful of gas, then switched to the NGKs. On the street, the colder of the NGK plugs weren't happy, and I changed them after about 30 minutes of around town driving. I've been running the hotter of the two (I think the 6's, but could have the number mixed up). I haven't run the Champions yet, but they were what I ran in the 70s, and I've got a set of the cross referenced part number that is available today. The Champions are in the trunk, in the event I need a swap... along with material to fix hose leaks, a set of accessory belts, a fuel pump, and tool kit.
The motor seems to really like the NGKs.
On consumption, when I used Rotella before the rebuild, the 1300 would consume this at about the same rate as the rebuilt motor. When switched to Mobil 1, the consumption diminished significantly on the older motor.
I'll be interested to see what consumption is like after the next tank.