I just today put Amsoil 15-40 marine diesel in that 1987 260 hp 5.7
Mercruiser as I have been doing for a couple years now. I'll know in
2500 hours whether it was a good move or not!

Capt. Jeff

K. Smith wrote:


Use the 40, if that's the recommendation.

The multigrade oils only thicken up when they get really hot
(various additives, plastics etc expand & change as the temp rises, but
the base oil is the lower claim, so a 20-40 is actually 20 grade oil
with additives to help when it gets hot), as in a properly thermostatted
car engine.

The trouble or one of the troubles:-) with raw water cooled engines
is they can't run the normal high (near boiling temp) thermostats, so
the engine & therefore oil might not get really hot & if it were
multigrade it "might" not thicken enough to give the engine proper
protection when worked hard.

Other end of the scale; some boat engines, skiing or heavy cruisers
can really put the engine to work & although the raw water low temp
thermo cools the block, still & all the oil can get hot, again 40 is
better than 30 in that case too.

K

I am sorry, but whoever "penned" the above obviously knows nothing about
lubricating oils & films.

K. Smith...: please post back and tell us this was some kind of joke or
flame...

Multigrade oils do not "thicken up" when they get hot, hotter, or really
hot. You can demonstrate this in your kitchen today with a quart of
your favorite 10W-40 and a candy thermometer.

As to the OP, straight 40 weight oil would be fine, espescially with the
older engines with seasonal use on Lake Erie, but for the high costs
involved with the ownership, maintenance, & possible replacement of
marine power, I recommend, and follow, that you use a multigrade Mobil 1
product for maximum protection - and Purolator Pure 1 filters.


Rob

On Wed, 06 Oct 2004 10:03:11 -0400, trainfan1
wrote:


Multigrade oils do not "thicken up" when they get hot, hotter, or really
hot. You can demonstrate this in your kitchen today with a quart of
your favorite 10W-40 and a candy thermometer.

This has been a source of endless debates between my friends and i. I
think most people understand multi-viscosity oils on some level, it's
just the terms are confusing. As long as you get that even though the
viscosity rating of a multi-weight oil increases as it gets warmer,
both straight and multi-viscosity oils are actually "thinner" when hot
you've got it.

On Wed, 06 Oct 2004 11:15:38 -0400, Slambram
wrote:

On Wed, 06 Oct 2004 10:03:11 -0400, trainfan1
wrote:


Multigrade oils do not "thicken up" when they get hot, hotter, or really
hot. You can demonstrate this in your kitchen today with a quart of
your favorite 10W-40 and a candy thermometer.

This has been a source of endless debates between my friends and i. I
think most people understand multi-viscosity oils on some level, it's
just the terms are confusing. As long as you get that even though the
viscosity rating of a multi-weight oil increases as it gets warmer,
both straight and multi-viscosity oils are actually "thinner" when hot
you've got it.

There you go.

Later,

Tom

OMG... Here we go again.
-Dan

"WaIIy" wrote in message
...

I have Mercruiser 5.7's 1989 and boat on Lake Erie near Cleveland.
My mechanic recommends straight 30wt oil and that's been fine, today he
said a new bulletin came out from Mercury and it was something like 30
wt up to 60 degrees F and 40 wt for over 60 degrees F.

Now my mechanic says to use straight 40 weight.

What do you think?

"K. Smith" wrote in message
...



The multigrade oils only thicken up when they get really hot (various
additives, plastics etc expand & change as the temp rises, but the base
oil is the lower claim, so a 20-40 is actually 20 grade oil with additives
to help when it gets hot), as in a properly thermostatted car engine.


K: Either you have just enough information to be dangerous or you badly
mis-stated what you were trying to say.

All oil, single or multigerade thin as they heat up. Multigrade oils just
don't thin out as fast.

If by "plastics" you meant "polymers" then part of what you said is correct.
A multigrade starts with a base that is comparable to the lower weight
number and adds polymers that react with heat. This reaction slows down the
thinning action, it does NOT reverse it.

What most people do not realize is that the two numbers are given from
entirely different tables. There is a range of viscosities that is covered
under the "W" range and another range of viscosity for non-W. An oil rated
at 75W has about the same viscosity as an oil rated at 10.

Another important aspect of the rating is the fact that SAE motor oil is
rated at 100 degrees C. When you need the viscosity this is the
temperature that you oil is likely to be at.

A multigrade oil allows you to have a higher viscosity oil at 100 degrees C
that you can still manage to pump out of the oil pan when the temperature
drops well below freezing. It comes at a price, however. The polymers tend
to be fragile, and can be damaged by excessive heat or contamination. A
20W-40 is a much more robust oil than a 5W-40 because it started with a
heavier oil and doesn't need as much treatment to stretch it out.

Putting additives in a multigrade oil is also taking a risk for the simple
matter that it may be impossible to tell how the additive might react with
the various polymers in the oil. I doubt that the additve manufactures
fully test against every possible brand and weight of oil, and even if they
did I doubt even more that they would let you know if they discovered a few
brands that reacted badly with their additive.

If you live in Florida then you really don't need to worry about multigrade
oils. Run 40 weight and you are fine. If you live in Bismark North Dakota
in the winter time a multigrade oil is exactly what you need.

Rod McInnis

rmcinnis wrote:
"K. Smith" wrote in message
...




The multigrade oils only thicken up when they get really hot (various
additives, plastics etc expand & change as the temp rises, but the base
oil is the lower claim, so a 20-40 is actually 20 grade oil with additives
to help when it gets hot), as in a properly thermostatted car engine.



K: Either you have just enough information to be dangerous or you badly
mis-stated what you were trying to say.

Yes & I apologise, sorry I was trying to show that a low temps multi
grade oils stayat their lower "grade", good thing you blokes are keeping
an eye on me:-)


All oil, single or multigerade thin as they heat up. Multigrade oils just
don't thin out as fast.

Yes

If by "plastics" you meant "polymers" then part of what you said is correct.
A multigrade starts with a base that is comparable to the lower weight
number and adds polymers that react with heat. This reaction slows down the
thinning action, it does NOT reverse it.

Yes again

What most people do not realize is that the two numbers are given from
entirely different tables. There is a range of viscosities that is covered
under the "W" range and another range of viscosity for non-W. An oil rated
at 75W has about the same viscosity as an oil rated at 10.

Another important aspect of the rating is the fact that SAE motor oil is
rated at 100 degrees C. When you need the viscosity this is the
temperature that you oil is likely to be at.

Yes & there is the rub with raw water cooled boat motors.

A multigrade oil allows you to have a higher viscosity oil at 100 degrees C
that you can still manage to pump out of the oil pan when the temperature
drops well below freezing. It comes at a price, however. The polymers tend
to be fragile, and can be damaged by excessive heat or contamination. A
20W-40 is a much more robust oil than a 5W-40 because it started with a
heavier oil and doesn't need as much treatment to stretch it out.

Putting additives in a multigrade oil is also taking a risk for the simple
matter that it may be impossible to tell how the additive might react with
the various polymers in the oil. I doubt that the additve manufactures
fully test against every possible brand and weight of oil, and even if they
did I doubt even more that they would let you know if they discovered a few
brands that reacted badly with their additive.

If you live in Florida then you really don't need to worry about multigrade
oils. Run 40 weight and you are fine. If you live in Bismark North Dakota
in the winter time a multigrade oil is exactly what you need.

Rod McInnis



Thanks Rod

K

rmcinnis wrote:

Another important aspect of the rating is the fact that SAE motor oil is
rated at 100 degrees C. When you need the viscosity this is the
temperature that you oil is likely to be at.


"K. Smith" wrote in message

Yes & there is the rub with raw water cooled boat motors.



One thing to keep in mind is that inboard and stern drive engines run with
hotter oil temperatures than their automotive cousins, even though their
coolant temperatures are around 140-165 vs. 180-210. An automotive engine
normally operates at a much lower power output and rpm (2500 rpm @ 70mph)
and air flow is constantly flowing over and around the motor while running
down the road. That air from the car's volocity and/or the radiator fan
absorbs the operating heat emitted from the engine and the oil pan.

In a boat, an engine is located in a cramped area and also is sometimes
insulated to reduce sound and heat transfer to the other areas of the boat.
There is no 70mph air flow helping to cool the motor or the oil pan. A
marine engine is cruising at a much higher rpm and power output for hours at
a time. The internal parts of the engine, pistons, rods, bearings, etc. run
at a much higher temperature than the 140 degree cooling water, and the oil
has to asborb that extra heat. The combination of limited air flow and
higher power output in a confined space make the oil in a marine engine run
quite a bit hotter than in cars. You can test this out by using an infrared
temp gun on your boat and your car if they use similar engines. It is
especially true if you run the car and the boat at the same speeds for
several hours.

In a previous post, Karen was correct in a way. When a multi grade oil gets
severely overheated, the oil can thicken up depending on its additive
components. Today's mulit grade oils are much more heat tolerant than the
ones from years ago.

Bill Grannis
service manager

When a multi grade oil gets
severely overheated, the oil can thicken up depending on its additive
components.

that is also true of single weight oils, but you knew that didn't you (you
being a service manager and all)?

petro lub oils usually get pretty damned gooey at about 300F, hence one of the
advantages of syn oils, which make it usually to about 500F.

petro oil can cause exhaust valve sticking in high performance engine of long
ago designed to run on leaded fuel (which lubed the valve stems and seats) that
now try to run unleaded.

"JAXAshby" wrote in message
...
..

that is also true of single weight oils, but you knew that didn't you (you
being a service manager and all)?




The discussion that you interupted concerns mult-grade oils.

Bill Grannis
service manager