Can you run synthetic in a freshly overhauled engine

You can use either synthetic or mineral based oil in any engine. Whether you should change or not mid engine would really depend on what was done in the overhaul. Something I recently learned, from an engine mechanic, is that you should not change engine oil brands mid way through the engines serviceable life. All oils contain an additive package and there is a real risk that one brand's package will strip out all of the previous package's parts protection and begin to add its own to the turning parts. This will, for a period of time, leave your turning parts with only the base oil itself to protect it.
If you have had a new crank, bearings, cam, and valve train installed, it would be my opinion, that now would be as good a time as ever to switch oils and brands. On the other hand, if there was only pistons, liners, and bearing installed, I would keep using what has always been used in it. Again, that's just my opinion ... good luck with your choice

 

Assuming you have warranty with that overhaul, I would be confirming the breakin requirements with the shop that overhauled it before you do that. I know some manufacturers want minimum hours/miles with conventional oil before you switch to synthetic. It's a two minute phone call.

 

An article in Overdrive suggested mineral oil changed at 3000 and again at 10000 miles. Then put your synthetic in. I think the author was Mallison. His reason was to use the cheaper oil to get the metal filings that will happen while breaking in.

 

I'd wait and see how much make up oil it needs in 10,000 miles. If it doesn't need any your rings are seated. If it needs oil it's gonna take more time for the rings to seat. I'd think synthetic would only prolong that time.

 

I have always been a fan of changing out the initial fill oil on a new or rebuilt engine before 10,000 miles. There is a lot of early wear metals floating around in that stuff. I don't use a synthetic on the first oil change, but have no problem going to synthetic at the second oil change. Break in is more dependent on how the engine is operated right out of the gate than a long period of time. Most all of break in is going to happen within the first 15,000 miles. The old days, it could be argued it took longer. But with the closer tolerances of engines of the last 15 years, most break in occurs early on. An operating the engine properly in that time frame has as much effect as anything on how it settles in. You don't want to be abusive, but you don't want to baby it either.

My present factory rebuilt 12.7, I did what I just mentioned above. Just about ready to turn over 300,000 with it, and it uses, maybe, around a half gallon of oil in 25,000 miles and averages high 7 mpgs year round. Oil samples are some of the best I have ever seen from any heavy diesel.

 

I know with all the new technologies out there and laser machining etc they say the tolerances in new engines are so bang on that they no longer need a break in and can run synthetic right out the gate.

That being said I don't know if that goes for old engines made new again.

The only reason they tell you to not run synthetic is because of the loose tolerances there used to be, you had to give time for your rings to seat properly and synthetic oil is too good and would keep that from happening.

I know I didn't exactly answer anything but hope it's better than nothing haha

 

X2 I know guys that will spend 20K on a car racing engine-but will break it in on conventional oil. I've did a few this way before going to synthetic. On my new diesel I went to semi synthetic on the first oil change.