viscosity synth/mineral

[bcrazy]

I'm new to this forum and i have some questions regarding the next oil change on my 91 Volvo 940 B230FB (2.3L NA)

The engine has 177k on it and has some piston slap on cold startup and idle, but next to zero oil consumption, and no slap ones warm. I want an oil that will help keep my piston slap noise down, but still be thin enough for tempereatures down to -25deg C (-14 deg F)

So far i've been changing every 3k with cheap 10w40 mineral. I'll probaly go for a 0w30 or 5w30/40 this winter, but i have not decided on brand or mineral/synthetic.


I've heard people say that a 10w40 synthetic is thinner than a 10w40 mineral. I can not understand how this can be. Isn't that why the viscosity is printed on the bottle? Do they measure different on syntethic than on mineral oils????

I really don't want to spend the money on REAL synthetic, and also believe because of my 3k intervals it's not needed.

I need advice

 

[tmorris1]

There is no viscosity difference between a mineral and a synthetic. 10W40 is 10W40 no matter if it is mineral or synthetic. If you do go to a "Real" synthetic like you stated you wouldn't have to do the 3,000 mile change, you could go a little longer for starters, unless you are worried about warranty.

 

[mikemc]

A moderately priced 5w40 synthetic like Shell Rotella may be a good choice. As stated above, a 10wXX meets only the 10w cold crank standard no matter what base oil. A 0wXX or 5wXX would be better for your cold climate. What viscosities does your owners manual recommend?

 

[Patman]

quote:

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Originally posted by bcrazy:



I've heard people say that a 10w40 synthetic is thinner than a 10w40 mineral. I can not understand how this can be. Isn't that why the viscosity is printed on the bottle? Do they measure different on syntethic than on mineral oils????

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No, the viscosity is measured the same, in order for it to get the 40 designation on it, the oil must have a viscosity of between 12.5 and 16.3 cst at 100c.

 

[MGBV8]

Oil viscosities are accurately measured in units called “Centistokes” at exactly 100 degC. These fall into five high temperature SAE catagories:-

SAE No. 20 30 40 50 60
Viscosity Range 5.6 -
A decent quality oil usually has a viscosity that falls in the middle of the spec, so a SAE 40 will be about 14 Centistoke units, but SAE ratings are quite wide, so it’s possible for one 40 oil to be noticeably thicker or thinner than another.

 

[427Z06]

Here's another example to scramble your brain. Listed below is two synthetics, one is on the very low side of the specs for a 0w-30, the other on the high side of the specs for a 0w-30.

code:

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Mobil 1 Castrol SLX

SAE Grade 0W-30 0W-30

Viscosity, ASTM D 445

cSt @ 40ºC 54.8 68.4

cSt @ 100ºC 10.1 12.0

CCS, cP, ASTM D 5293 3800 @ -35ºC 5200 @ -35ºC

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So, if you compare a "light" 10w40 synthetic to a "heavy" conventional 10w40, one could state the synthetic is lighter for the same grade, and vice versa.

If I haven't totally confused you, let me know, I'll give it another go.

 

[Mickey_M]

quote:

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Originally posted by bcrazy:
I want an oil that will help keep my piston slap noise down, but still be thin enough for tempereatures down to -25deg C (-14 deg F) .....

I've heard people say that a 10w40 synthetic is thinner than a 10w40 mineral. I can not understand how this can be. Isn't that why the viscosity is printed on the bottle? Do they measure different on syntethic than on mineral oils???? ....

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A little piston slap doesn't hurt anything. I wouldn't choose an oil specifically to reduce "piston slap noise".

That said, a synthetic *may* reduce the noise because it clings to the metal after it is shut down and you don't have quite the "dry start" you have with a mineral oil. Many synthetics have some ester in them, and esters excel in sticking to metal surfaces.

The other issue is viscosity and low temperature performance. The two are related, but it's not a one-to-one correspondence.

Viscosity is measured at a specified temperature and it measures the time it takes for the oil to flow through a given aperture.

In the real world you're more interested in how the oil flows and pumps over a range of temperatures. Again speaking generally, a synthetic may exhibit superior low temperature flow and pumping properties compared to a non-synthetic.

I'd try a middle-of-the-road mass market synthetic and see what you think of the results.

 

[bcrazy]

i just bought some pemco 5w40 synth
Anyone who knows anything about this?