I would like to change to synthetic oil, but I am wondering how to get the old oil out completely as I understand you should not mix the two. I have to suck the oil out the dipstic so I do not get it all. I also don't think you drain the oil cooler and lines completely. Is it necessary to get it all out? I know there are a number of you out their that have changed to the synthetic oil, so what did you do?

I've broken new engines in with reg. oil and then switched to syn. with no problems. If it really worrys you , only run it a few hours and change it (and filter) again. What's left at that point won't be worth worrying about.

ttt

should you use the same weight oil with synthetic? I have stock 502's 425hp am thinking of switching to mobil 1. is any one syn better than the other? Also, does the frequency of oil changes differ?

No need to sweat about getting the old oil out. They'll mix with no problems.

Yes, use a synthetic with the same "weight" as conventional oil. Synthetics are actually different in the way their viscosity behaves at different temps and such than conventional oils, so they just stamp on the can what conventional oil the synthetic behaves like.

(synths remain pourable when cold and do not lose lubricating properties at the same heat ranges as conventionals).

In a boat, your oil change interval is set by the need to remove contaminants in the oil from blowby and combustion byproducts that get in the oil and remain in suspension by the detergents in the oil - not from oil breakdown. Therefore, the fact that synth oil will last far longer before breakdown is not a concern, you gotta change out the contamination on the same schedule. This means that oil change intervals remain the same.

Use cheap oil for your change before winter layup and then change it again after a couple of hours in the spring to your good stuff.

Use Mobile 15-50 -- look for the red stripe on the container and would suggest a Fram HP4 oil filter.

Not A Problem.

I ran the Merc stuff in a Baja 212 with 454, a 272 with 502 and the 36 with 500's until 20 hours on each.

Then I switched to Mobile 1 15W50 in each, using the Fram HP4 filter and sometimes the Merc Racing Filter.

I have received VERY good service out of all these engines.

Don't worry about making the change.

Why does my merc manual say not to use synthetic oil & multi visc?

You beat me to it. The Merc website specifically states that you should not use synthetics. Anyone know why?

I run the M1 15/50 with no problems. There might be better oils out there and cost more money but M1 is the best bang for the buck.

Dock Holiday, What's your experience w/ those Vortec filters? Any better performance than w/ the K&N's? It's time for new one's for me and am deciding if they're worth the extra $$$$. Found the K&N's on Eddie Marine's site for around $60.