Just finished a full rebuild (crank, rods, pistons, etc...) how long should I wait before I switch to synthetic oil?

I have read that you should wait at least 5000 miles minimum for car motors. I would suggest doing an oil analysis to determine when the engine has broken in (less fines in the oil after break in period). Sometimes new engines use oil until broken in and then don't use any after that. If you were going to wait for the equivalent of 5000 miles for your boat motor that would be around 150 hours. The danger is using it too early. I think and oil analysis might be the way to go.

I think it's fair to say 150 hours in a boat is a he!! of a lot harder than 150 hours in a car . I switched to synthetic @ 15 hrs and never looked back. No problems

Oh, this was at the advice of the engine builder.

Yea, 150 hours is a long time. Tek-5 has oil analysis kits and they get back to you in around 2 days.

Mercury Marine used to consider a MerCrusier engine broken-in when it came back to the dealer for the 20 hr. check. --- Jer

The only thing you should worry about are the rings seating. If it was finish honed properly and your using good rings, a few hours is all it needs. 10-15 max, usually one weekend.

Dan

My builder tells me that rings will seat in 2-3 hours. In that time, vary the throttles a lot, and keep it under 4000-4500, with maybe a few SHORT spurts at WOT. Then suck out the old, in with the new and you're good to go.

Don't forget to change the oil filter with the oil change.

Life is good, eh?

Brian

The guy who just rebuilt one of my HP500s said the same thing. Run it for 2-3 hours and change to synthetic.

With todays technologies and their capability to get precision bores, 2-3 hrs are sufficient for break in.

Use it a weekend then replace with synthetic.