I bought my truck a month ago. To check the health of the engine and to insure the block wasn't toast, I sample the engine oil when I replaced it. According to the dealer records which they faxed me, there was less than 1800 miles on the oil.

My results showed that in less than 1800 miles whatever oil the dealer put in it, I am sure as cheap as possible, went from a 14.6 viscosity at 100 degrees to 14.07 viscosity at a 100 degrees. The lab stated that the oil was still good for use. That is a loss of 3.7 percent viscocity in 1800 miles.

I will report back and let you know how the synthetic matches up.

BTW I e-mailed shell and asked them if the Rotella started from a synthetic base stock. There first answer was that it was a synthetic priprietary blend of oil. I then wrote them back and asked did the proprietary blend was all synthetic. They have refused to answer over the last couple of days. The Rotella is a hydro-cracked dyno oil, further refined, so I would not use an extended drain interval with this oil (Amsoil recommends only 7500 miles max for a car on this type of oil). It sucks that the US government ruled that they can market this stuff as "real" synthetic.

 

I'm curious how you were able to determine the initial viscosity of the oil when you don't know what brand was used.

Also, could you please post the other results of the UOA - it would be interesting to see this info.

 

Bottom line I don't know the initial viscosity, however I good new oil is usually is only 14.6. So I use that number for my comparison, it the oils initial viscosity was less than that why would you buy it?

 

Well, for it to qualify as SAE 40 the viscosity can be anywhere between 12.5 and 16.3 cSt at 100*C, so I don't know how anyone could tell, without testing, what you were starting with. 14.6 is only slightly above the middle of the allowable range - I'm not sure how you have determined that that means it is "good".

Remember, just because it lists a particular viscosity on a spec sheet doesn't mean that is exactly what you're getting. There are variations between batches.

 

I think that a 3%-4% delta in viscosity is well within manufacturing variations batch to batch. That is why the spec for a 40w has such a wide range.