How is the 40 degree C measured, confused.

[Drewie]

I am trying to understand how the low temp cSt readings are measured, I have been comparing a couple of oils I am thinking of trying, one is a 15w40 oil and the other is a 10w50 oil.
The confusing thing is that looking at the manufacturers specs the 15w40 oil has a reading of 112 cSt at 40 degrees where as the 10w50 oil has a reading of 132 cSt at 40 degrees, I realise the 10w50 will be thicker at operating temp ie 100c but why would the specs on a 10w appear to be heavier than a 15w oil at the 40c reading? When cold would the 10w mentioned above be thicker than the 15w mentioned above.

 

[Rand]

you need the VI to do that calculation
or the viscosity at 40c and 100c

 

[Zako2]

The 10W and 15W ratings are for below freezing flow properties, not at 40C. 50 grade is thicker than 40 grade at operating temperatures as well as in a pretty wire range below 100C.

 

[Drewie]

Thanks for the replies, I have a car with a slight bit of piston slap when cold and I was going to try a slighly heavier oil when cold.
The 15w40 oil was listed as 14.4 cSt at 100c and 112 at 40c.
The 10w50 oil was listed as 19.2 cSt at 100c and 132 at 40c.

I did not realise the 10w and 15w were for below freezing flow rates and could not understsnd how the 10w appeared heavier at the low temp than the 15w. So from those specs above would the 10w be slightly heavier at start up when the ambient temp was say around 20 degress C.

 

[Ran23]

Changing your oil viscosity will not help your piston slap. Piston slap occurs when piston cools and the metal shrinks and the is more gap between the piston and cylinder wall. So oil will not keep you piston from shrinking. I believe manufactors do this to cut costs on materials. Your best thing to do it let it slap. Wont hurt a thing!

 

[mechtech2]

A thicker oil will help with piston slap [or any other loose parts]. The amount of help will vary car by car. But it is in the right direction - don't go nuts with high viscosity.

How can it NOT help/address this situation?
Answer: Who would recommend a LIGHTER oil for piston slap?

 

[SteveSRT8]

I've owned many a GM "slapper" and oils made no difference.

One is still a-slappin' at 400k + miles!

 

[A_Harman]

I've experimented with using thicker oils to quiet my LS1 piston slap. Couldn't hear any difference going from 30 to 40-weight.

 

[ProfPS]

Don't forget that 40°C = 104°F & 100°C = 212°F

 

[Coprolite]

Originally Posted By: A_Harman
I've experimented with using thicker oils to quiet my LS1 piston slap. Couldn't hear any difference going from 30 to 40-weight.

So it didn't go from thwack thwack thwack to thwock thwock thwock?

 

[A_Harman]

No, it's pretty much just clack, clack, clack for the first few minutes on a cold start. I have found that revving the engine up to 1500 rpm eliminates the slapping noise.

 

[Hounds]

Originally Posted By: Ran23
Changing your oil viscosity will not help your piston slap. . . Your best thing to do it let it slap. Wont hurt a thing!

QED

 

[Hounds]

Originally Posted By: Coprolite
Originally Posted By: A_Harman
I've experimented with using thicker oils to quiet my LS1 piston slap. Couldn't hear any difference going from 30 to 40-weight.

So it didn't go from thwack thwack thwack to thwock thwock thwock?

LOL

 

[SteveSRT8]

Originally Posted By: A_Harman
No, it's pretty much just clack, clack, clack for the first few minutes on a cold start. I have found that revving the engine up to 1500 rpm eliminates the slapping noise.


Anyone with an LS type engine and high miles should consider some Kreen in the oil and gas first if they have startup noises. I have now taken three extremely high mileage examples from noisy start up to near silent with Kreen.

These engines are known for 'carbon knock' which many confuse for slap or a bad lifter, etc.

 

[A_Harman]

The car has had cold-start piston slap since I took delivery on it new. I was all torqued off about it originally, but the dealer said it was normal. I thought; "OK, so I'll see you at 35,000 miles for a new engine under warranty." But it never came to that.

I do run quarterly treatments of RedLine's fuel system detergent, and it doesn't affect the noise.