ivangene

I call BS - this is a bigger issue than something to just blow off.... YES - IF you drive the car, the moisture will be "burned off" however - ALL internal combustion engines trap water and IF NOT burned off, it will accumulate enough to be an issue -

I killed a car with this as I worked only 4 miles away.. and on my way to work i would drop the kids off after 3/4 mile, then go to my Mother in laws another 3/4 mile away, then the post office.... 3/4 mile, then the store... 1 mile, then work... 3/4 mile. - at lunch I would run out for a quick 2 mile trip, and back... then after work - I would stop at my hangout 1/2 way home.... I never thought I was killing the motor... but it got realy rusty inside... I mean really rusty! (changed oil every 3-4k miles) - over time it killed it -

Iit can happen and if you have a short drive to work and the car doesnt warm up - it WILL happen......

I dont know if that is over "exagerated" - but it is true and CAN happen

1999Porsche911

Isn't that exactly what I said?

smackboy1

The SAE viscosity grade is just brushing the surface. There are a lot of other factors that determine the optimal performing oil for a specific application. For example depending on the ambient temps the cold start viscosity of a 0W vs. 5W oil can be inconsequential to engine wear. IMHO the best way to optimize an oil for a particular engine application is through used oil analyses (UOA).

The forum for amateur (and some professional) tribologists is here

http://bobistheoilguy.com

For convenience I quoted these from the BITOG glossary:

centistoke (cSt)

The worldwide unit of kinematic viscosity.

VI (Viscosity Index)

An arbitrary scale used to show the magnitude of viscosity changes in lubricating oils with changes in temperature. Oils with low VI number such as VI=0 ("zero") have high dependence of viscosity change on temperature. They thicken quickly with decreasing temperature, and thin out quickly with increasing temperature. Oils with high VI number such as VI=200, will still thicken with decreasing temperature but not as rapidly, and also will thin out with increasing temperature, but again not as much as low VI oil.

VI number can also be "negative"

Tables found in ASTM Method D 2270 are widely used to determine VI number.

However, VI does not tell the whole story -- it only reflects the viscosity/temperature relationship between temperatures of 40°C and 100°C. Two lubricants or base oils with the same VI number may perform dramatically different at low temperatures in the -5°C to - 50°C range.

LVDell

So then if I am looking at comparing 2 oils (made up numbers) with cSt@40C of 75 and 125 respectively and cSt@100C of 15 and 20 respectively, what the hell does that mean?

Let's throw the viscosity index into the mix with them having 200 and 150 respectively.

How about HTHS of 3.5 and 4.5 respectively?

Tippy

I am far from an expert on oil and do not have a Fluid Engineering degree to back up my statements but a friend told me just use "racing" oil and you'll be fine.

They're loaded with ZDDP.

Being lower detergents, you do have to change it more frequently though.

The cats? Who cares, I would rather replace them than the valvetrain (in the M96).

1999Porsche911

What's so hard to understand?


The dynamic or absolute viscosity:

τ = μ dc/dy (1)

where

τ = shearing stress

μ = dynamic viscosity

Equation (1) is known as the Newtons Law of Friction.

In the SI system the dynamic viscosity units are N s/m2, Pa s or kg/m s where

1 Pa s = 1 N s/m2 = 1 kg/m s
The dynamic viscosity is also often expressed in the metric CGS (centimeter-gram-second) system as g/cm.s, dyne.s/cm2 or poise (p) where

1 poise = dyne s/cm2 = g/cm s = 1/10 Pa s
For practical use the Poise is to large and it's usual divided by 100 into the smaller unit called the centiPoise (cP) where

1 p = 100 cP
Water at 68.4oF (20.2oC) has an absolute viscosity of one - 1 - centiPoise.

Kinematic Viscosity
is the ratio of absolute or dynamic viscosity to density - a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with it's mass density

ν = μ / ρ (2)

where

ν = kinematic viscosity

μ = absolute or dynamic viscosity

ρ = density

In the SI-system the theoretical unit is m2/s or commonly used Stoke (St) where

1 St = 10-4 m2/s
Since the Stoke is an unpractical large unit, it is usual divided by 100 to give the unit called Centistokes (cSt) where

1 St = 100 cSt
1 cSt = 10-6 m2/s





Kinematic Viscosity will only determine how fast the oil will flow without pressure. Higher viscosity means oil will stay on components while engine is off, longer than a lower viscosity.

It is the Dynamic viscosity that determines how the oil protects the engine as it defines the extent of shearing while under pressure. Mayonaise has a higher Kinematic Viscosity than most oils yet its dynamic viscosity is lower.

Also look for a high HTHS rating.

ivangene

awe - yea... ^^^^^^^

this would be the part where I get blamed for sitting on my a$$ and not researching -

Hey look, something shiny !!
BTW fwiw - I too am planning this retrofit bearing -

medtech

1999,

I know it's difficult, by try not to be a total a@@. Charles is not some amateur shmo off the street, and he was kind enough to chime in on this thread. Those kind of assinine comments are exactly why respected experts refuse to participate in our threads.

1999Porsche911

You need to develope some thicker skin.

medtech

You need to hone your social skills...

LVDell

I can't believe nobody tried the "I'm rubber you're glue" defense yet.

Macster

Yes, a fully warmed up engine if driven long enough can boil off a considerable amount of water.

But of course this water didn't collect all during the previous fully warmed up engine run time of 30 minutes.

If the engine is started and driven until fully warmed up and for some time after the amount of water the engine crankcase accumulates will be minimal.

But dare I say this type of usage is not as common as the other kind, which involves short trips, alot of cold starts and the engine and oil seldom get up to operating temperature and stay there long or long enough.

Shortly after I first got my 02 Boxster in Jan of 2002 -- when I lived in the mid-west -- I had the oil analyzed and IIRC -- I have the analysis report at home -- the water content was nearly 7%.

Granted this is high, higher than I thought it would be cause I drove my Boxster approx 10 miles to and from work at speeds from 30mph to 45mph.

After the analysis I started paying more attention to the coolant temperature and noted that in the cold weather at that time of year the coolant temperature didn't hardly get above 180F (and I did *NOT* use the in-dash gage for this but used an OBD scan tool to monitor actual coolant temperature in real-time) even after 10 miles of moderate driving.

Once every couple of weeks I'd drive 70+ miles at freeway speeds to my parent's house using the car. Even during these drives the coolant would barely climb into the mid-190F range. If I had the autoclimate control set to auto to keep the cabin warm and dry to avoid window fogging in the cold weather the electric radiator fans would run and keep engine coolant temperature way below 212F.

Now I know engine oil runs hotter than the coolant but these engines equipped with an oil heat exchanger which works to keep engine oil temperature lower than it would be otherwise.

As a result the coolant has to get pretty hot before I assume the engine oil temperature is at least water boiling hot. What I use is if the coolant temperature 212F or higher I assume the oil is at least that hot and thus any water in the oil being boiled away. But in the meantime that water is present and doing its worst.

Which is one of several reasons why I decided on following a 5K mile oil/filter service interval.

Sincerely,

Macster.

medtech

Aw Dell! I was savin that one for my final cou de gras! Now ya ruined it.

Charles Navarro

The oil runs about 10 degrees over the coolant temp, maybe more if in traffic in a tip car when the ATF builds extra heat that gets shed into the coolant as well.