As far as I can figure out, switching to synthetic right away will just make the break-in period take a little longer. By break-in, I mean the period for everything to seat properly and start sealing well. It still breaks in just as well but the period of poor mileage due to a new engine lasts a bit longer.

Looking at torn down engines which have started with synthetic, they still break in just as well, there is no long term damage.

 

Infedel it is a good ideal to break your vehicle in on petroleom oil . An as a general rule it takes longer to break in a diesel . Which can depend somewhat on how your useing it . If your really working it hard an useing them for what they were designed for breakin will come sooner . That being said I would not hesitate to put it in anything with 15000 on it .

 

Funny how these threads keep going on. wilson already changed his oil (I assume to Amsoil).

I used to think the no synthetic on a new engine was a leftover rule from the old days. Recently, after dealing heavily with John Deere on engines I decided the rule is still valid. JD went a step further and requires their 10W-30 petroleum with a very high level of ZDDP additive on all new and major rebuild engines. The high ZDDP packs extra zinc into the scuff areas (cam lobes, tappets, piston walls, lifters, etc.) Reminds me of the very old days of using #10 non detergent on an engine rebuild.
IIRC, the first oil change on JD must be conventional oil. After that you can use synthetic.