Originally Posted By: fpracha
Originally Posted By: Gokhan
Originally Posted By: fpracha
So back to the 15W-40 again... do these oils leave VII deposits or much more of other types of deposits?
In your experience are these deposits mainly generated during much extended drain intervals or even during shorter drain intervals ?
And will these 15W-40 oils cause the sluggishness and poor fuel economy due to original viscosity being thicker, OR due to the deposits they leave in engines?
With synthetic oil, deposits could only be a worry in turbocharged engines.
Coming back to my experience, switching from 15W-40 HDEO to first 5W-20 dino and then 0W-20 synthetic, I am seeing the best performance with the 0W-20 synthetic. I think the thinner synthetic has really cleaned the engine and it's also giving better performance due to lower HTHS viscosity. The engine is certainly running smooth, but in most part it's thanks to good maintenance, especially of the carburetor and emissions. Note that I wouldn't be able to make the switch to a thinner oil if I hadn't replaced the valve-stem oil seals because the oil consumption would be too high. Before then I was adding about 1 quart every 1,000 miles and with 0W-20 I would have to add about a quart every 250 miles. Now, the oil consumption is almost zero.
OK thanks
But are the Synthetic 5W-20's not good enough in comparison to the synthetic 0W-20's ?
I was looking at the below, seems really close to a synthetic 0W-20 oil but put forward as a 5W-20 by the manufacturer:
Monolec® Tetra-Syn™ Engine Oil 8521
SAE Grade .......... 5W-20
Density(60ºF/60ºF).. 0.850
Visc 100°C, cSt .... 8.46 typical
Visc 40°C, cSt .... 44.72 typical
Viscosity Index ... 171
FP °C(°F) ......... 215.6 (420)
PP °C(°F) ......... -42 (-43.6)
Acidity mg KOH/g .... 2.55
TBN ................. 7.59
LINK:
A full synthetic SAE 5W-20 gasoline engine oil passenger cars and light duty trucks
Does this look like a 0W-20 to you ? All comments welcome, thanks!
Well, the x in xW-y only refers to the really cold temperatures (such as -20 C, -40 C, etc.) and the y refers to 100 C. The temperatures in between (such as 40 C, 20 C) are not part of the SAE xW-y viscosity specs. Therefore, you cannot really tell anything by looking at the 40 C number.
That said, 0W-20 oils should usually run thinner than 5W-20 at temperatures such as 20 C, 40 C, etc. because they usually have a higher viscosity index. In fact, the definition of the viscosity index is a look-up table involving the 40 C and 100 C viscosities (you can use online calculators to calculate the viscosity index from the 40 C and 100 C viscosities). Having a high viscosity index oil, such as Toyota 0W-20 SN, Eneos 0W-20, etc., will ensure that you have an oil that runs still as thin as possible when the engine is cold, which is always a good thing.
All said, this oil doesn't have a high viscosity index. It certainly looks like a 5W-y, not 0W-y, but again only the really cold specs can tell that. But then the pour point looks like a 5W-y as well. Toyota and Eneos 0W-20 are well over 200 in viscosity index.
This is not to say that 0W-20 is superior to 5W-20 in all ways. It's definitely superior in viscosity characteristics -- you want the highest viscosity index possible for best fuel economy and engine protection with a cold engine. But then 0W-20 is more volatile than 5W-20 because it uses thinner base oil, which could increase oil consumption and high-temperature deposit formation.