switch to synthetic ?

[Quint4]

I should know better than starting an oil thread but here goes anyway..... I am thinking of switching my 1992 7.4 merc with 700 hrs from dino to synthetic oil. Synthetic is at the top of Mercs recommended list. I have heard you may cause trouble (ie. leaking seals) by switching from dino to syn on an older motor.
My 7.4 runs great and I want to do all I can to keep it that way. Opinions ?

 

[NorCal Boater]

I switched a year ago on 7.4s with 500 hours and have had no problems with leaks. My goal was to be able to go a bit longer between changes as oil changes on my 340 are a pain.

 

[Hampton]

Merc says that it is approved for use in all of their engines, new and used. It is a synthetic blend. Maybe very little synthetic oil, but a lot more profit.

 

[chris41483]

There are very few true synthetics readily available. Most are man-doctored dino oils. They have few advantages over dino, don't waste your money. However, a true synthetic has many benefits, do your research before you spend your money.

 

[tdappleman]

As has been posted - most 'synthetic' oils on the market are actually synthetic blends. Keep in mind - Synthetic oil is engineered dyno oil - the idea is to have the molecules be of consistent shape and size to ensure better flow and lubricating qualities. The better the base stock which the company starts with, the better the end product will be. You can do some searches on that one and then formulate your own opinion. One thing to keep in mind is to ensure you have the correct certifications on the oil you end up with - primarily FC-W or Four Cycle - Water. This is key as it shows the oil can handle the moisture and control corrosion in your engine.

This link shows the current oils which have met the FC-W certification: http://www.nmma.org/certification/programs/oils/fc-w.asp


You wont run into problems by switching to a synthetic at this point - they are not going to make your engine leak or consume oil any more than you would if you were using dyno oil. I recently switched from the Mercruiser 25w40 to Amsoil 10W40 Marine which is FC-W rated. I've noticed more consistent oil pressure between the two engines after the switch but no other significant differences yet.