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#4652324 - 01/31/18 04:43 PM UOA additive level is much higher than the VOA ?
Cressida Offline


Registered: 10/16/02
Posts: 474
Loc: Joplin
I just got my UOA back on a 4k mile sample of Rotella T5 10w-30 (this is the prior version CJ-4/SM) that I'm using in an old Toyota (gas engine). Overall it's a very good report that I'll post later. However, I note the zinc on my UOA is showing 1,540ppm and the VOA of this oil is never more than ~1,200ppm. This lab is normally good so I would doubt it's an error and will not be asking them to re-run it.

I believe additives like calcium, phosphorus are used during the oil run and often see them lower on the UOA. How does my zinc level increase over 300ppm (1,200 > 1,540) during the sample period? I don't recall seeing anything like that in the past.

This was my first use of the Rotella T5, so is this an example of the oil "cleaning" or leaching old zinc that had been deposited on the metal surfaces? confused
---------------

In addition, I see sodium showing up at 200ppm and this Rotella has no sodium in the VOA. Before we guess coolant, I'll mention the lab checks for glycol (Schiff’s reagent method - ASTM D2982) and reported "negative antifreeze detected"; and there is no confirming potassium or silicon that might point towards coolant. Furthermore, Oxidation doesn't seem to be an issue and was reported at 18%.

After looking over all my data, my best guess is the sodium could be left over from prior oil because I see my prior oil was with a Smitty's brand that shows 400ppm sodium in the VOA. I did use a small amount of Hylomar gasket sealer in the corners of a new valve cover gasket during this run but can't tell if Hylomar could be a contributing factor...

Would this seem reasonable to have this amount of residual sodium from the prior oil, and does prior sodium normally take time to come out ?

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#4652414 - 01/31/18 06:07 PM Re: UOA additive level is much higher than the VOA ? [Re: Cressida]
MolaKule Offline


Registered: 06/05/02
Posts: 19042
Loc: Iowegia - USA
Yep, it's called "additive carryover."

What did the current oil's VOA show?

Formulae do change.


Edited by MolaKule (01/31/18 06:10 PM)

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#4652486 - 01/31/18 07:17 PM Re: UOA additive level is much higher than the VOA ? [Re: MolaKule]
dlundblad Offline


Registered: 09/30/13
Posts: 10012
Loc: Indiana
Originally Posted By: MolaKule
Yep, it's called "additive carryover."

What did the current oil's VOA show?

Formulae do change.


That, or somebody somewhere was wrong.
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#4660673 - 02/09/18 08:24 AM Re: UOA additive level is much higher than the VOA ? [Re: Cressida]
weasley Offline


Registered: 03/13/13
Posts: 749
Loc: UK
Originally Posted By: Cressida
I believe additives like calcium, phosphorus are used during the oil run and often see them lower on the UOA. How does my zinc level increase over 300ppm (1,200 > 1,540) during the sample period? I don't recall seeing anything like that in the past.

Additive elements don't go away, they generally stay in the oil but in different forms. Zn and P levels shouldn't really change much over time, although the structure of the molecules they are in does.

Two ways to see higher UOA than VOA elemental numbers:

1. Carry-over, as Molakule says
2. Volatility; base oils will tend to evaporate more readily than additives and so with a really hard-used engine you can see additive concentration through volatility.
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