multi-wt. mtr. oil viz incr..~

the scuttlebutt was at one time that as multi-weight motor oil in the crankcase aged,

the viscosity increased. fact or fiction, and if the condition existed at one time - does it still apply?

it stands to reason that as the oil becomes saturated with impurities and a portion of

the additive package becomes depleted - that the viscosity would increase.

back to square one, why does the viscosity increase - in the beginning?

and how does the "synthetic rubber" polymer in multi-wt. motor oil affect the viscosity?

mho v=83e

Reply to
fiveiron
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In a gasoline engine, normally the oil will thin because it gets diluted from the gas that gets past the rings. In a diesel engine, the viscosity stays pretty close to the same. In a propane or natural gas burning engine, the viscosity will slightly increase, or in other words, thicken. I'm sure somebody will give some exceptions.....

Reply to
Kruse

I sent in a sample of 5W-30 synthetic for analysis after being in the engine for 13,000 kms and it showed to be 8W-30, still acceptable according to the lab. Semi diesel trucks can get a gadget that monitors the viscosity while in the engine. When the TAN (Total Acid Number) and TBN (Total Base Number) levels intersect on a graph, it's time for replacement. The Noack Volatility also affect the viscosity.

Reply to
rudyxhiebert

I've had several oil analyses done over the years, and the fuel content reading has always been below the threshold (0.5%) and was likely lower. This included the factory fill from a new engine as well as a 12K mile extended drain experiment.

The fact is that multiweight oils with VI improver tend to drop viscosity when the VI improver breaks down. The typical conventional 5W-30 will test in the high 20 range after 5-7K miles. However - a typical API sequence test is supposed to result in thickening due to volatility burnoff and oxidation.

One of most interesting motor oils I've heard of is Mobil 1 0W-40. The whole idea is that Mobil has geared it towards both meeting fuel economy tests AND extended drain requirements.

1) It starts off on the low end of the 40 range. 2) VI improver breaks down such that it's in the 0W-30 range for most of its useful life. 3) Eventually it thickens via oxidation such that it tests at 40 weight at the end of the extended drain test. The measurement points are only at the beginning and end. 4) The fuel economy test is over the entire life of the oil, so being thin most of the time helped.
Reply to
y_p_w

Go here, and read your brains out:

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Reply to
EatMe

Fact. All long-term oil analyses that get posted to the Bobistheoilguy website show some viscosity increase with age. I don't think its just the viscosity improvers that cause it, either.

Reply to
Steve

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