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From what I've found out about the synthetic oil being used on break-ins, here goes:
Using a full synthetic oil for break-in will not seat the rings. ie.....you'll burn oil for a LONG time.
GM has talked to Mobil about this so an additive was added to Mobil 1 to alleviate this problem. Mobil 1 has been the factory fill in Vettes since '92!
So if you WANT to use synthetic for break-in, ONLY use Mobil 1 or a synthetic you KNOW has the additives to alleviate the problem.
Good information. MTI did the 10-15 startup procedure on my 396. Then put in Castrol regular oil. They said I could change over to Mobile 1 between 700-1000 miles on the new engine.
Mine came back from LPE Broken In. I asked if I should be easy on it...my answer was "NAIL IT" :D I dumped the oil and switched to synthetic around 1000 miles....all's been well since. It's durable.
Just talked to the builder, he said he's got some dyno castrol he was planning on putting in it for about 15 minutes, change the oil, and then put the castrol back in. He said after 500-1000 miles that I could put what ever I wanted in it, but I should plan on putting in whatever I want to use the rest of the engine's life (synth. or dyno). I'm sticking with synthetic since GM recommends it.
I guess at like 750 miles I'll change it to Mobil 1.
I've always ran 20 minutes at about 2000rpms for break on 30wt dino oil. I make sure I have a water hose running in case the temp wants to go up although it never has. Change oil using the dino oil and a new filter. Then drove around varying rpms and load staying between 25% to about 75% of each until 2000 miles then went with the Mobil 1. After that I just drive it however.
This is another subject that is loaded with HYPE. Think about this....every car comes off the lot new and is never broken in. people been buying them and driving them off the lot with no changes in driving habits. Tons of old beaters still around today. Break it in the same way your gonna drive it....period.