WaIIy wrote:
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?

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

On Wed, 06 Oct 2004 05:40:04 GMT, WaIIy
wrote:


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?

Karen has pretty much hit it. Straight 40 weight if that's what the
manufacturer recommends.

However, you might want to discuss with him the age of the motor and
if it's lasted this long on the 30/40 combination, then why not stick
with it?

Later,

Tom
-----------
"Angling may be said to be so
like the mathematics that it
can never be fully learnt..."

Izaak Walton "The Compleat Angler", 1653

ignore K's advice in its entirety, for K's has shown herself to be utterly
ignorant in the subject with this line:

The multigrade oils only thicken up when they get really hot

read the whole thing if you can stomach it.

"K. Smith"
Date: 10/6/2004 5:48 AM Eastern Daylight Time
Message-id:

WaIIy wrote:
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?

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

mercruiser does not build engines, it assembles marine systems. ask the
manufacturer of the engine for its advice, and then go with the 20w-40 it
recommends. Then replace your mechanic, or be prepared to spend some money
with him

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?

I'm using Amsoil 15-40 marine diesel in my 1987 5.7 liter and am happy
with it so far. Ask me whether I'm still happy in 2500 hours.

Capt. Jeff

On 06 Oct 2004 12:04:58 GMT, (JAXAshby) wrote:

mercruiser does not build engines, it assembles marine systems. ask the
manufacturer of the engine for its advice, and then go with the 20w-40 it
recommends. Then replace your mechanic, or be prepared to spend some money
with him

Where did you find GM's reccomendation of 20w-40 oil for a marinized
engine in a marine application? Can you substantiate that or did you
just pull it out of your ass?

Go with Mercruiser's reccomendation. And Karen's advice is correct.

WaIIy wrote:
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?


Mercury recommends 25W-40 oil for Mercruiser engines, back in '89 they
rcommended straight 30 weight. In '89 Mercury sold 30 weight and warned
against multi-viscosity oils, now they recommend and sell it.

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

Short Wave Sportfishing wrote:




Karen has pretty much hit it. Straight 40 weight if that's what the
manufacturer recommends.


Tom

Multigrade oils do not "thicken up" when they get hot, hotter, or really
hot.

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.