Re: How often should i change the oil?
 

I use Castrol 20w50 conventional oil. It looks like golden honey when it is new and I change it when it begins to get dirty which works out to be something like every 25 hours or so. Conventional or the super sophisticated, expensive Synthetics .....when it's dirty none of it is any good!

Re: How often should i change the oil?
 

Mercruiser no longer does not recomend semi-synthetic, because they now have a semi-syn out under their label. :D

I saw a Merc service video once and the guy from Merc said the reason they said no synthetic was that synthetics did not have the anto corrisive additives needed in the marine environment.

I think:
1) if you're changing the oil every 20 hours, that won't matter
2) At least Amsoil had and has an oil specificly for Marine and Diesel applications which does contain the anti corrisive additive. I'm sure others do now too, but like I said, if you're changing the oil often, it doesn't matter.

In the 7.4 MPI I ran Amsoil 15w-40 HD Marine and Diesel but in the new motor I've been running 50w Valvoline Racing Oil and changed it at about 10 hours then ever 20 after that. Since March when she was first fired, I have about 45 hours and 2 oil changes with one due now.

Re: How often should i change the oil?
 

Change it!

Re: How often should i change the oil?
 

Good question. Can anyone comment? I don't think I would be comfortable running oil that sat in the crankcase all winter, even if it was changed in the fall.

Re: How often should i change the oil?
 

I'll run it 5-10 hrs in spring and then change.

The small amount of condensation will burn off.

Good point above re: acidity in the used oil sitting over winter.

Will do more damage than condensation.

Re: How often should i change the oil?
 

Eggzackly!! I use conventional oil as well. IMHO...it's a waste of $$$ to use synthetic if you are going to change it every 25 hours.

Re: How often should i change the oil?
 

In honor of all you conventional oil users I hereby post this.. :D

Re: How often should i change the oil?
 

20 hours period. Conventional all the way... until someone proves that synthetics do anything better than conventional at normal temps and 20 hour changes... :rolleyes: :rolleyes: :stupid:

Re: How often should i change the oil?
 

Has anyone done any kind of oil analysis to determine that 20 hours is the limit? At 50 bucks and a good hour an oil change, i don't want to be doing it every two weeks unless i absolutely have to. It takes forever to suck all that oil out through the dipstick tube.

Re: How often should i change the oil?
 

I've done a couple of oil analyses, and I probably could have gone longer. The oils I used (Kendall & Mercruiser) were hanging in there very well. But I think if I were pushing it longer I might go synthetic. These motors are pretty tough on oil...

I've never seen an oil analysis on synthetic posted.