I don't know what Merc recomends but my builder with ProCharged 720 HP 454's says VR1 50 only.
My $.02

Its still a 50 weight. Period. People on here are so stuck on whether its a 5w, 10w, 15w or 20w. As long as the protection is still a 50, it will work just fine.

Only at 210 F.

Ken

what stands for the 5? and i ask here in holland about the 20w50 that is a semi shyntetik oil and the 5w50 a full,

wil the 5w50 be to low when the oil is cold? does the oilpump not suck up the oil?

please can anybody explane?

thanks

let me ask differend

why is there a full a semy and a non syntethic oil?

The bigger the spread between the small (5W) and big (50) numbers the more viscosity enhancers that are needed.

Viscosity enhancers shear and the oil reduces viscosity faster.

20W-50 has much less enhancers and is much preferred for marine engines.

The 5w is the cold temperature, therefore the oil will be able to pump quicker at startup, therefore providing better lubrication protection. The 50 is the operating temperature rating, a 50 is preferred for the high output, racing type engines, i.e. marine applications.

Maybe this little caption will help too.....

Viscosity Improvers
Mineral oil lubricants become less effective at high temperatures. The drop in viscosity with heat reduces their film-forming ability. Unbelievably, to try and counter this problem, seasonal oil changes used to be the norm for some applications! Fortunately, with the advent of viscosity improvers, this is no longer the case.

Viscosity improvers are polymers added to low viscosity oils to improve high temperature lubrication. They effectively thicken the oil as temperature increases. This means that the lubricating effect of mineral oils can be extended across a wider temperature range.

A balance between thickening efficiency and shear stability is important when selecting a polymer for use as a viscosity improver. Higher molecular weight polymers make better thickeners but tend to have less resistance to mechanical shear. Lower molecular weight polymers are more shear resistant, but do not improve viscosity as effectively at higher temperatures and therefore have to be used in larger quantities.

Polymer additives can also undergo thermal and oxidative degradation, unzipping back to smaller monomers, which reduces their effect. The highest possible degree of thermal and oxidative stability is desirable in addition to the features above.

Viscosity improvers are primarily used in multigrade engine oils, gear oils, automatic transmission fluids, power steering fluids, greases, and some hydraulic fluids.

Here is one more real good explanation, also not biased......
http://www.oil-shop-uk.co.uk/acatalo...ear-stable.pdf

Basically, you get what you pay for

Ask a Merc certified mechanic about using 5W-50 in say Florida and see what he says...

Just because he is certified, doesn't mean he knows JACK Sh## about oils.

I believe you will not find many (if any) marine engine builders who will recommend 5w50 oil. I will not risk an expensive engine with something out of the norm.