I'm curious if any of you guys run synthetic in your 496's. I was reading the mercruiser manual and it does not recommend running synthetic! WHY????

I just switched my 496's to Mobil 1 15-50 during winterization from Mercruiser 25-40. I use Mobil 1 in every motor I own but still read the thread on Marine Lubrication here on this forum before the switch. I'm not sure why Mercruiser does not recommend synthetic other than after reading the above thread I learned that the lubrication properties of the Mercruiser 25-40 is like no other petro based oil and that there are large differences in the synthetics lubrication properties. I also learned that the fuel blow by & moisture in marine engines may effect the recommended lubrication.
Hopefully someone with some run time on their 496 with synthetic oil will chime in.

My Merc manual for my 496 HO's recommends Merc Synthetic 25X40.

What year? My 02 496 HO's manual states just like pachanga's, synthetics not recommended.

Mines an 03. Perhaps in later years they determined that synthetic is a better choice?

have run the M1 in my two '02 HO's for 200+ hours no issues.
40 hour change intervals.

Harley Davidson never recommended using a synthetic until they marketed one.
When did Mercury start to sell a synthetic 25w40?
Ken

I have the 2002 496Ho and I tries running Mobil 1 Synthetic oil in it , and I noticed lower oil pressures and a small oil leak near the front of the engine. I switched back to Mercury oil (non-synthetic) and the leak went away and the oil pressure returned to normal? I guess some engines like the synthetic oils and others don't? I run full synthetic oil in my diesel truck and in my car and never had any oil leaks or oil pressure issues.

Which Mobil 1 oil did you try ?

I run Mobil 1 15W-50 in my 496. Carries just as much oil pressure as 20W50 Kendall. There is NO reason not to run synthetic in a 496 MAG HO. At one time there were rumors of the roller tips on the lifters sliding across the cam lobes as opposed to rolling across them but that has proven to be a non-issue. Ilmor Viper marine engines come factory filled with Mobil 1.