Can Synthetic oil cause oil leaks?

JLAS

Hey guys, 
I have Volvos 5.0 on my 320, and am about to make an oil change.  Apparently, the previous owner has been using Quicksilver 25-40.  I would like to make a change and Mobil 1 Synthetic 15-50.  The guys at the shop where I got the oil told me that often synthetic oils will cause a motor that has been using conventional oil to leak.  Has anyone experienced that?  Should I continue with the Quicksilver brand?

Thanks in advance.

frodo13056

Actually, there are quite a few articles on-line about using synthetic vs conventional oils for automotive applications - everything from engines, transmissions, differentials, etc. 
Seems like a lot of folks agree that if you have equipment that is around 10 years old or has lots of miles (or in a boat's case - lots of hours) that using synthetic will cause older seals to start leaking. Most companies that make synthetic oils say that they design the molecules, etc. to create less friction, fill gaps and things like that. What they don't mention is the potential negative impact to older or high mileage equipment seals.
If it were me, I'd stick with a known good scenario and stick with the conventional at this point. If you were dealing with a newer boat then synthetic would be a good option. I've had my 2008 320 since new and have always used the conventional engine oil recommended by Mercury Marine. 

[Deleted User]

I've used synthetic oil exclusively in my 2003 Sierra Denali pickup with 155K miles. No signs of oil leaks. It isn't even "weeping" oil from the valve covers. Are there "articles" on this topic or just "forum posts?" Big difference.

Andy

Handymans342

I tried synthetic on my Suburban one time. Leaked like crazy. Had to go back to high miles oil. 

Handymans342

Same thing happened in my buddies 4 runner

brandonmayberry

I worked many years in an auto parts store and this came up fairly often. I have always been told and lead to believe that you can use synthetic or conventional but don't use conventional for a long period and switch. The reason is that the conventional oil soaks into the seals and O-rings and causes them to swell and seal up and when you change to synthetic it will lose that conventional oil in the seals and they will begin to leak. Im not sure of how accurate the claims of this are, but its what i was taught by mechanics who have been in the industry for many years.

BellevilleMXZ

No Ive never seen it, and i'm an auto tech......thatsaid I'd stick to the quicksilver, or rotella T6, both are a HD, "newer" design and formulated than the mobil. That mobil is an old formulation. Both of them do very well in oil tests in boats

JLAS

Thank you all for the nice info. The boat has 27 hrs and originally had Volvo oil which I believe is synthetic. Then, the marina apparently changed it to Quicksilver a couple times. I guess we will see what happens.  I will keep you updated.  Volvo is calling for synthetic so  I will keep my fingers crossed. :-)