Being quart low - would skew UOA?

dilettante · Jan 2, 2005

You BITOG folks are so smart - sorry if this question has been asked a million times before. My 330Ci has a 7 quart case - and I usually change her oil (M1 or Syntec) at 15k miles, and at least 1 quart low (why waste a quart when you're just going to drain it). Would being a quart low (6 qt vol) somehow skew the results of a UOA? Especially because everything is reported in units of ppm - or would it not matter so much since the vol. is so large.

Can't wait to take GC to 15k miles.

Cheers.

Gene K · Jan 2, 2005

Most of the guys around here are so nano picky that if their car got 100 ml low they would be adding from a graduated beaker.

You can just multiply your wear metals X 0.86% to get a more representative result. Of course if you add the Qt you could likely run 17,000 mi instead of 15,000 mi with close to the same numbers.

Whem you add the Qt you are essentially giving the oil in the engine an Additive and TBN boost.

Gene

haley10 · Jan 2, 2005

I like Castrol Syntec and Mobil 1.

I'm sure you know that only GC and M1 0W-40 meet BMW LL specs.

Running Syntec and other M1 products for this duration might not be a good idea.

I would not go beyond 7.5K in any car without uoa's telling me it's ok.

ruking77 · Jan 2, 2005

You are absolutely positively correct!! So if you ADD one quart to bring back the oil level, you have just made your previous 6 qt sample 14% better. So another way to look at it is you can now do a 17,000 mile oil change rather than at 15,000 miles. Or your oil analysis sample is really 14% better than it tests! (depending upon whether you add the quart before or after the sample) So the .86% makes all the sense in the world.

However, I have the same gig going on, and do not add before the change. I do 15,000 mile intervals and 2 of my vehicles (TLC's) consume 1/4 to 1/2 qt at app 14,000 miles. I just wait till I change and do not add.

Don Stevens · Jan 3, 2005

quote:

Originally posted by ruking77:
You are absolutely positively correct!! So if you ADD one quart to bring back the oil level, you have just made your previous 6 qt sample 14% better. So another way to look at it is you can now do a 17,000 mile oil change rather than at 15,000 miles. Or your oil analysis sample is really 14% better than it tests! (depending upon whether you add the quart before or after the sample) So the .86% makes all the sense in the world.

However, I have the same gig going on, and do not add before the change. I do 15,000 mile intervals and 2 of my vehicles (TLC's) consume 1/4 to 1/2 qt at app 14,000 miles. I just wait till I change and do not add.

I practice something similar....My 4.6 modular burns about 1 qt per 5000-7500 miles. I use the low oil level time to change my filter, take a sample and top up. I sample the oil before adding the new oil so as not to skew the TBN
number.

In dilettante's case, his wear metals are indeed more concentrated than if the car had not used any oil. Most of the UOAs we see here on synthetic oils in passenger cars are so good the 14% slightly less oil volume is not going to show that much more metals.

Don

Gary Allan · Jan 3, 2005

So, is the consensus that we're just diluting concentrated particles?? That is, the particles stay in the remaining oil? None of those particles are part of the consumption that enters the combustion process via the rings (vary depending on a few factors)? All of the consumption is assumed to be from volitilizing and vaporizing the oil, leaving the solid material behind??

What if the lost quart takes its share of stuff away with it? I would imagine that it would vary depending on how you consumed the quart of oil.

RJCorazza · Jan 3, 2005

quote:

Most of the guys around here are so nano picky that if their car got 100 ml low they would be adding from a graduated beaker

Oh no... I just bought a glass beaker for that very purpose. My bike is 8.4oz low at the center of the sight glass.

Al · Jan 3, 2005

Well..I think the answer is somewhere in between 14% and nothing. If it used that quart in the last 10 miles then it would be just like draining a quart of oil and taking a sample=zero difference if it burned the quart in the first 10 miles then it would be the entire 14% bc its running with a quart less the whole interval. Its some kind of intergral function between the two..but I'm not motivated to figure it out.

Gary Allan · Jan 3, 2005

quote:

Most of the guys around here are so nano picky that if their car got 100 ml low they would be adding from a graduated beaker

What's your point

quote:

I just bought a glass beaker for that very purpose.

What took you so long? Every BITOG member should have a Pyrex® 1000ml beaker for accurate measurements and heating/cooling experiments. A 100ml is useful as well.

dilettante · Jan 3, 2005

quote:

Originally posted by Al:
Well..I think the answer is somewhere in between 14% and nothing. If it used that quart in the last 10 miles then it would be just like draining a quart of oil and taking a sample=zero difference if it burned the quart in the first 10 miles then it would be the entire 14% bc its running with a quart less the whole interval. Its some kind of intergral function between the two..but I'm not motivated to figure it out.

Don't think too hard, please

Actually, she burns about a quart every 2500-3000 miles (M1 especially), so a quart low situation occurs through the last 2500 miles.

Thanks all for the thoughtful responses. About what I thought. 14% better numbers. That will make the GC 15k numbers look even better. Something about green oil really appeals to me. Although purple oil is good too.

Not to re-hash old controversies - but with a 7 quart case full of synthetic (probably any group and brand), a make-up quart at least every 3k miles, and 99% highway miles, our UOAs are bound to look good!

Cheers.

dilettante · Jan 3, 2005

quote:

Originally posted by haley10:
I like Castrol Syntec and Mobil 1.

I'm sure you know that only GC and M1 0W-40 meet BMW LL specs.

Running Syntec and other M1 products for this duration might not be a good idea.

I would not go beyond 7.5K in any car without uoa's telling me it's ok.

Don't get too sucked in to the LL or A3 spec. There's plenty of other oils out there that can go the distance. For example see Paradise Garage M1 5-30 Oil Study - not LL and not even A3.
Actually, I'm gonna start testing various ones starting with RP.

Cheers.

Pablo · Jan 3, 2005

Yes it would skew the results. Consistency for your own purposes is the key, IMHO (just so I don't get a soap box gremlin).

IOW - your top-up adds should be the same timing for meaningful comparisons.

So basically you add around 4-5 qts per 15K mile OCI?

JohnnyO · Jan 3, 2005

Which is why Blackstone asks you how much make-up oil you've added. They allow for it, i.e. my mother's 2-stroke Caddy Northstar got an outstanding UOA at 6 or 7000 miles (I forget) but then we added 3 quarts over that time and it was low when I drained it.

dilettante · Jan 4, 2005

quote:

Originally posted by Pablo:
Yes it would skew the results. Consistency for your own purposes is the key, IMHO (just so I don't get a soap box gremlin).
IOW - your top-up adds should be the same timing for meaningful comparisons.

So basically you add around 4-5 qts per 15K mile OCI?

Ya, about 4 quarts with M1 0-40. Something about that oil - it crawls right up the cylinder sleeve and out she goes.

I think I know what you're thinking - why bother even draining the pan - it's all practically new oil in there! I'm sure this topic has been beaten to death...
Syntec is better in not burning off so fast - but of course, it's not Group IV. Thus, my new hobby of trying to find just the right oil to go the distance and not burn.

Cheers.

Pablo · Jan 4, 2005

Have you considered the Amsoil 5W-40?

I can say one thing about this oil it seems to be a very low consumptiom oil.....I'll be commenting on this when I do my first UOA on this oil, but so far the level has not budged on the wife's car...and this car has always used some oil.

Norm Olt · Jan 5, 2005

Oil Analysis results (+ or minus "x" percent)
TIMES a possible
"Zero to +14%" increase in oil volume of (+ or -)?

= What?

Apples & Oranges!

Cheers!
Norm

Gary Allan · Jan 6, 2005

quote:

Thus, my new hobby of trying to find just the right oil to go the distance and not burn.

Rotella T® 5w-40 or Delvac 1® ..I'd lean toward Rotella just because of your consumption. Gallon constainers would appear to work for you.

Being quart low - would skew UOA?

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