As the season draws to a close I am thinking about fluid changes in my new
to me boat. I have 1987 Mercruiser 260s and the manual recommends straight
30W oil. Why not a 20-40W or a 20-50W? The manual says that's ok if
straight weight is not available but it is not recommended. Can anyone shed
any light on this for me? Thanks.-DanO

You do not have the huge temperature differentials that cars have. Most of
the time you are in the 40-75 degree ambient temperature range.
Bill

"Dan Olstad" wrote in message
ink.net...
As the season draws to a close I am thinking about fluid changes in my new
to me boat. I have 1987 Mercruiser 260s and the manual recommends
straight
30W oil. Why not a 20-40W or a 20-50W? The manual says that's ok if
straight weight is not available but it is not recommended. Can anyone
shed
any light on this for me? Thanks.-DanO

"Dan Olstad" wrote
the manual recommends straight 30W oil.
Why not a 20-40W or a 20-50W? The
manual says that's ok if straight weight is
not available but it is not recommended. Can anyone shed any light on this
for me?

Disclaimer: This is free advice and you get what you pay for.

My understanding is that the reason single grade oils are recommended for
boats is to reduce internal corrosion in your engine. Because a single grade
oil is thicker at lower temperatures than an equivalent multigrade oil, it
sticks to the bits and pieces inside your engine better after you shut it
down and things in there cool off.

Now, about those Ws. Your manual probably recommends an SAE30 and those
multigrades you're looking at are probably 20w40 and 20w50s, not
number-numberWs. The W stands for winter and what it's all about is the
temperature at which the viscosity rating applies. If there's no W, the
viscosity rating is measured at a high temperature, probably something like
212 degrees Fahrenheit. If there's a W attached, the rating is measured at a
cold temperature, like maybe zero degrees Fahrenheit. A 20W oil has 20
somethings (what that number actually means is kind of mysterious, at least
to me, so I like to just think of it as a relative thing) at zero degrees
and would be less viscous, ie lower number, at 212 degrees. An SAE20 (with
no W) oil would be more viscous, ie higher number, at zero degrees than a
20W. At any rate what 20w50 means in oil lingo is that at zero degrees
Fahrenheit it has the characteristics of a 20W oil and at 212 degrees
Fahrenheit it acts like an SAE50. They make all that happen by adding
polymers that wrinkle up or stretch out depending on the temperature, making
multigrade oils thin out less as their temperatures rise and thicken up less
as their temperatures fall than single ones do. This is great for cars,
especially in cold weather, because it gives you a relatively thin oil at
startup, so it circulates nicely around the cold engine, and then it stays
thick enough once the engine warms up to keep things nicely lubricated. And
since car engines are typically used frequently and seldom sit around in a
moist bilge, it's not a terrible problem that the oil drips off of the
innards relatively easily when the engine cools off.

All of the above may be total BS, but I did get it from a reliable source, I
think, but unfortunately that was so long ago that I don't remember who or
how reliable that source might have been.

All of the above may be total BS, but I did get it from a reliable source, I
think, but unfortunately that was so long ago that I don't remember who or
how reliable that source might have been.

I think its BS.
My Mercruiser manual says to use 5-40.

What the hell is that? so 10-40 isn't good enough? Real reason is to
cause F.U.D. to discourage boat owners from doing work themselves.

John C.

bill, knock it off. straight weight oil takes many, many, many seconds longer
to flow to all pressure oil bearings in a just started, ambient temp engine
than does multi-weight oil.

straight weight oils are proper only for engines that are started with proper
care to prelube and brought up to temperature before putting a load on it and
are run for extended periods of time before shutdown.

bill, you don't have a clew what the paragraphs above mean, so just knock it
off and don't post again on oils.

"Calif Bill"
Date: 9/18/2004 10:04 PM Eastern Daylight Time
Message-id: . net

You do not have the huge temperature differentials that cars have. Most of
the time you are in the 40-75 degree ambient temperature range.
Bill

"Dan Olstad" wrote in message
link.net...
As the season draws to a close I am thinking about fluid changes in my new
to me boat. I have 1987 Mercruiser 260s and the manual recommends
straight
30W oil. Why not a 20-40W or a 20-50W? The manual says that's ok if
straight weight is not available but it is not recommended. Can anyone
shed
any light on this for me? Thanks.-DanO

My Mercruiser manual says to use 5-40.

What the hell is that? so 10-40 isn't good enough? Real reason is to
cause F.U.D. to discourage boat owners from doing work themselves.

no, 5w-40 lubes better upon ambient temp engine startup that 10w-40 and much
better than 30w or 40w does.

however, the difference between 5w-40 and 10w-40 isn't all that great. In
past, 5w-40 didn't hold up as well under long service, and so was seldom sold.

"JAXAshby" wrote in message
...
My Mercruiser manual says to use 5-40.

What the hell is that? so 10-40 isn't good enough? Real reason is to
cause F.U.D. to discourage boat owners from doing work themselves.

no, 5w-40 lubes better upon ambient temp engine startup that 10w-40 and
much
better than 30w or 40w does.

however, the difference between 5w-40 and 10w-40 isn't all that great. In
past, 5w-40 didn't hold up as well under long service, and so was seldom
sold.

Thanks all. With all that, I don't see any reason that a 20w-40 or 20w-50
would not be a preferable choice to plain old SAE 20, 30, or 40 which are
all recommended in my 1987 manual.
-Dan O.
Minneapolis

With all that, I don't see any reason that a 20w-40 or 20w-50
would not be a preferable choice to plain old SAE 20, 30, or 40 which are
all recommended in my 1987 manual.

operating weigh above recommendations can harm seals. thus using 20w-40 in
place of 20w doesn't do any good for lubing upon engine startup and can do some
harm when the engine is warm.

some people are under the mistaken impression that multi grade oils "thicken
up" as they warm up. they don't. they just thin out less as they warm up.

Well jaxass, how come cars have successfully run for years with straight
weight? My Ford 351W in the boat calls for straight 30 weight. You again
show you are even dumber than asslicker and that is hard to accomplish.

"JAXAshby" wrote in message
...
bill, knock it off. straight weight oil takes many, many, many seconds
longer
to flow to all pressure oil bearings in a just started, ambient temp
engine
than does multi-weight oil.

straight weight oils are proper only for engines that are started with
proper
care to prelube and brought up to temperature before putting a load on it
and
are run for extended periods of time before shutdown.

bill, you don't have a clew what the paragraphs above mean, so just knock
it
off and don't post again on oils.

"Calif Bill"
Date: 9/18/2004 10:04 PM Eastern Daylight Time
Message-id: . net

You do not have the huge temperature differentials that cars have. Most
of
the time you are in the 40-75 degree ambient temperature range.
Bill

"Dan Olstad" wrote in message
link.net...
As the season draws to a close I am thinking about fluid changes in my
new
to me boat. I have 1987 Mercruiser 260s and the manual recommends
straight
30W oil. Why not a 20-40W or a 20-50W? The manual says that's ok if
straight weight is not available but it is not recommended. Can anyone
shed
any light on this for me? Thanks.-DanO

Around 9/19/2004 10:32 PM, Calif Bill wrote:

Well jaxass, how come cars have successfully run for years with straight
weight? My Ford 351W in the boat calls for straight 30 weight.


As does the Crusader 220 in my dad's Chris...



--
~/Garth - 1966 Glastron V-142 Skiflite: "Blue-Boat"
"There is nothing - absolutely nothing - half so much worth doing
as simply messing about in boats."
-Kenneth Grahame, The Wind in the Willows