Is it important for an Oil to stay in grade?

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I used to think so, but seeing people running all kinds of higher weight oils like 20w-50 in vehicles that should be running 5w30 weight oil and not having any issues makes me wonder what difference it really makes if any.
 
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Of course it is. When an oil thickens due to oxidation, you want to change it out. Letting it go can lead to sludge.

You seem to be confusing two different subjects. Running a 50 grade oil in an engine spec'd for a 30 grade has nothing to do with staying in grade. An oil's ability to stay in grade is based on it's oxidation resistance.
 
But if I get a 5w30 and it goes out of grade to a 40 or 50 weight and many people are running those weights anyway, what will it really hurt?

Or am I still not getting this?
 
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Originally Posted By: ZZman
But if I get a 5w30 and it goes out of grade to a 40 or 50 weight and many people are running those weights anyway, what will it really hurt?

Or am I still not geting this?


Originally Posted By: buster
...When an oil thickens due to oxidation, you want to change it out. Letting it go can lead to sludge.
 
So does that mean it is thicker than a 50 weight then? At what point is the oil so thick that it becomes sludge?

Are you saying the Oil grade is not important and that the oxidation level is?

A 50w of oxidized oil is bad but a 50w of unoxidized oil is not.
 
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Originally Posted By: ZZman
But if I get a 5w30 and it goes out of grade to a 40 or 50 weight and many people are running those weights anyway, what will it really hurt?

Or am I still not getting this?


Are you being serious?
 
Originally Posted By: buster

Are you being serious?


I am serious.

I am curious because of the high weight of oil many people run in their vehicles with no apparent ill effects.

Is it going out of grade itself that is the issue or the reasons behind it going out of grade that appears to be a problem?
 
Dino oils tend to shear a bit at first, and then as time goes on, they start to thicken back up b/c the lighter ends of the oil, basically, start to 'boil off'.

You SHOULD be changing dino oils before they start to thicken up - which is why most UOA's you see, the oil is slightly thinner than the specified grade.

Long drain synthetic oils are a bit different - they are built to be stout enough that they can 'take' some of this thickening, and still protect well. So you will see long drains of syn oil (10k+ miles) that are at the upper end of their visc. grade, or into the next one, and the oil is still good. That is why you want to stay in the specified grade for extended drains - you will most likely be going up one oil grade anyway.
 
Remember that lubrication has more to do with the Flow of the oil to the part that needs lube. If there is thicker oil there is less flow.

I say stick to what the manufacturer recommends, either what is on the fill cap, or what is in the manuel. The manufacturer sets standards for their lubrication for a reason.
That being said, I have gone 1 grade heavier, from 5w20 to 5w30, however it does get above 100 degrees here in the summer and it gives me peace of mind.

I will probably go back to PP 5w20 after my 2 Auto RX clean and rinse cycles, but that might be a year or so from now the way things are going.
 
Nice question! I always asked myself the same thing.

And on oil analysis, where can you see if the oil is thicker than what is suppose to be? the viscosity result I guess?

If so, for example, is it the test at 40 degres or 100 degres and how do you read if it has thicker or it is tinner?
 
I think what Zman is asking is if a spec'd 30 weight goes out of grade and becomes a 50 weight, and should then be drained, how can people BEGIN with a 50 weight and have it work for them?
 
Like previously mentioned, it's the shearing and thinning that I would be concerned about.
Any thickening would be from way overused and abused oil.
 
So shearing thins and oxidation thickens?

**Going back to what i said earlier, is the fact that a 30w thickens to a 50w the problem or is it the process of oxidation that caused it to become a 50w the problem? Are you guys saying that if a oil goes out of grade any amount or a tad that it means it is shot?
 
Hi,
ZZman - Taking the ACEA's Test protocols as an example they are mostly "stay in grade" for the testing process. That is they stay with the grade parameters they started at

Engine manufacturers set their own condemnation limits concerning viscosity when using UOAs (in use).

A typical criteria states:

Viscosity @ 40C cSt
% Max Increase - 40%
% Max Decrease - 15%

Note that the 40C test point is used and not 100C test point that you seen commonly on BITOG UOA reports. This provides for greater accuracy

Some engine manufacturers may require the lubricant to "stay in grade" for extended periods over and above the likes of the ACEA protocol before "Approval" is given and the lubricant Listed

In modern engines, loosing some viscosity is a LOT less important than gaining some viscosity. Many modern engine components depend on known flow and viscosity characteristics

This is why it is important to always use the viscosity recommended by the engine's manufacturer for the ambient range expected
 
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A used 30 cum 50 wt. and a new 50wt. are very different things, I think. The old stuff has gotten thicker from pieces sticking together, and the new stuff is still differentiated and looser. Also acidified and AW and other adds are used up. The only thing that may be better new vs. old is heat transfer, the extra soot will help the older oil carry more heat.
 
I'll keep my 'theoretically' higher temperatures, lol.
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You got it ZZman. As an aside, some base oils are better than others at keeping those enlarged, polar, oxidized oil molecules solubized. Generally, solubility of them goes as Group: V > I > II > III > IV.

That is, in general, for a given additive package effectiveness, a motor oil with more polar (higher solubility) base oil mix will hold "its own waste" better. Gross analogy intended. Varnish/sludge can be gross looking anyway so it seems appropriate.
 
In addition to what JAG said, dispersants are effective against sludge as well. Esters can be effective in dissolving varnish and preventing high temperature deposits. Detergents also.
 
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