Oil change question

daz

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We know there are a lot of holdover ideas from days gone by that are no longer valid because certain things have changed. This seems like a stupid idea but it DOES seem to make sense. I like everyone have always changed my oil with a hot engine, waiting just long enough so that i don't burn myself. But back in the day when that idea was first born out of what seems obvious, oils were single grade. With today's multi grade it just hit me that draining oil cold with say 10w-40, the oil would be 4 times thinner ! Seems crazy to even consider a cold change, but why doesn't that make sense? What am i missing?
 
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You are missing that even at ambient air temps all motor oils will be thicker than when at normal operating temp. Here are the properties of Mobil 1 high mileage oil, note they are all more than 5 times thicker at 40C than they are at 100C
Code:
Typical Properties
 	        5W-20	5W-30	10W-30   10W-40   
SAE Grade	 	 	 	 
Viscosity (ASTM D445)	 	 	 	 
cSt @ 40 ºC	50.1	69.2	78.1	95.9
cSt @ 100 ºC	8.6	11.7	12	14.71
 
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Oil is always thinner when hot - the measurements (the 10W & the 40) are taken at different temperatures. The W # is relative to other oils all measured when they are cold too. Does it hurt to drain oil when it's cold - I personally don't think so.
 
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Nothing. Draining the oil hot just allows you to get it drained faster and to get more of it. Probably get more contaminants out too. I have noticed that I can only get about two or three ounces more of oil when I use the one drip every twenty seconds. That takes more than two hours. Drain it cold if you want to. I'm sure everyone does it differently. Regards
 

daz

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Not sure i get this. At operating temps the weight is far lighter than when cold? So the weight is nothing more than a way to compare oils, and working weight never approaches the listed weight because thats spec'd when cold? is that it?
 
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I have always drained my oil from an ambient temperature engine. Did it again just yesterday in fact. I've never had a lubrication issue with any vehicle I've owned over the past 36 years. I guess some might call me crazy, but keep in mind "normal" is synonymous with "average". I typically fall at one end or the other of a statistical Gaussian distribution curve (bell curve). Usually to the right.
 
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Originally Posted By: daz
Not sure i get this. At operating temps the weight is far lighter than when cold? So the weight is nothing more than a way to compare oils, and working weight never approaches the listed weight because thats spec'd when cold? is that it?
The first number, followed by the "W", is the comparative weight (To a single weight oil) when cold. The second number, following the "W" is the weight when hot, (Think 100C) comparable to a single weight of that number, when hot. So, a 5w/30 acts like a 5 weight oil when cold, but as a 30 weight oil when hot. A 30 weight single grade oil is a whole lot thicker at 30 degrees than a 5 weight........But a 5/30 is thinner at 100C than a 5W is at 30 degrees. Read that half a dozen times......It will start to make sense.
 
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Originally Posted By: 4wheeldog
So, a 5w/30 acts like a 5 weight oil when cold,
No it doesn't. The first number is just a representation of how an oil will behave at a measured temperature which happens to be at -35C for a "5w". But it's a pumping viscosity, not to be confused with kinematic viscosity that is represented by the second number in the oil grade. Saying that it acts like a 5 weight oil is inaccurate. http://www.upmpg.com/tech_articles/motoroil_viscosity/
 
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Draining when hot means that contaminates are still in suspension and far more likely to be removed during drainage. Fluid flow is greatly increased during hot drainage making for a more complete evacuation.
 
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Originally Posted By: Quattro Pete
Originally Posted By: 4wheeldog
So, a 5w/30 acts like a 5 weight oil when cold,
No it doesn't. The first number is just a representation of how an oil will behave at a measured temperature which happens to be at -35C for a "5w". But it's a pumping viscosity, not to be confused with kinematic viscosity that is represented by the second number in the oil grade. Saying that it acts like a 5 weight oil is inaccurate. http://www.upmpg.com/tech_articles/motoroil_viscosity/
Read it again.......I don't think that article says what you think it does. It only acts like a 5 weight oil, when cold, as I stated. It may not be exactly like a 5 weight, but it is labeled 5Winter for a reason.
 
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Settling velocities for really, really small particles (smaller than my oil filter is removing) in the Stokes regime are quite high, even in less viscous fluids, and 'cold' oil is even more viscous than 'hot' oil . . . I remember calculating settling times for such particles of metals in a short column of water back in college; they would often be measured in years by the time you got all the scientific notation off the seconds of settling time after cranking through the equations. A 'cold' drain evacuation is fine for me. I'm happy with keeping my oil pump's pickup primed and such.
 
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Originally Posted By: Nyogtha
I typically fall at one end or the other of a statistical Gaussian distribution curve (bell curve). Usually to the right.
*goes to look this up as such fancy words aren't usually found here on BITOG*
 
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Try changing the oil without warming the engine and see how it works for you. If you are OK with the extra time it takes to drain the oil, then go for it. If you are like me, and can't stand the extra time wasted while waiting for the oil to drain, then you will never do it again. A few oil changes ago, I decided to try an oil change with a cold engine. My reasoning was that all the oil would be in the pan, and not up in the galley, etc. Thus, a cold oil change would get more of the old oil than a warm change. My typical routine is I start the oil draining first, then remove and replace the filter. By the time I get the filter taken care of, the oil is done draining, and I can close the Fumoto valve and refill the oil. Works quite well. Well, the time I tried changing oil with a cold engine, when I was done with the filter, the engine was still draining. And so I waited. And waited. Then I went in the house and fixed a snack. By then, the oil had stopped draining, and I was able to move on with the rest of my routine. Oh, and have I mentioned that I run with 0W-20? I'll never do it again. But hey. Give it a try. If it works for you, that's all that matters.
 
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Originally Posted By: 4wheeldog
Read it again.......I don't think that article says what you think it does. It only acts like a 5 weight oil, when cold, as I stated. It may not be exactly like a 5 weight, but it is labeled 5Winter for a reason.
If you don't like Quattro Pete's [correct] explanation, then read SAE J300.
 
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Originally Posted By: Quattro Pete
Originally Posted By: 4wheeldog
So, a 5w/30 acts like a 5 weight oil when cold,
No it doesn't. The first number is just a representation of how an oil will behave at a measured temperature which happens to be at -35C for a "5w". But it's a pumping viscosity, not to be confused with kinematic viscosity that is represented by the second number in the oil grade. Saying that it acts like a 5 weight oil is inaccurate. http://www.upmpg.com/tech_articles/motoroil_viscosity/
This
 
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Originally Posted By: Chris Meutsch
Originally Posted By: Nyogtha
I typically fall at one end or the other of a statistical Gaussian distribution curve (bell curve). Usually to the right.
*goes to look this up as such fancy words aren't usually found here on BITOG*
thumbsup A humble example of my truth in advertising - I'm clearly an abberation cool As Popeye always said, "I Yam what I Yam!"
 
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By the time I get the car situated on the ramps, it's warm enough to drop the oil. That also gives the oil an opportunity to circulate through the engine and get a good oil film everywhere. I'm not so much about getting all the old "bad" oil out.
 
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No. You are wrong and are ridiculous if you want to argue further.
Originally Posted By: 4wheeldog
The first number, followed by the "W", is the comparative weight (To a single weight oil) when cold. The second number, following the "W" is the weight when hot, (Think 100C) comparable to a single weight of that number, when hot. So, a 5w/30 acts like a 5 weight oil when cold, but as a 30 weight oil when hot. A 30 weight single grade oil is a whole lot thicker at 30 degrees than a 5 weight........But a 5/30 is thinner at 100C than a 5W is at 30 degrees. Read that half a dozen times......It will start to make sense.
I found this to be the best and simplest:
Originally Posted By: OVERKILL
You are completely confused as to how the viscosity system works. The number in FRONT of the W is the "Winter" rating for the oil and is the measure of the oil's RESISTANCE to thicken as the temperature plummets. The number AFTER the W is the SAE grade of the oil as measured at 100C. Both a 0w-20 and a 5w-20 thicken as the temperature drops. This goes for any oil. They are both heavier at 90C than they are at 100C. They are both significantly heavier at 0C than they are at 100C. The difference is that the 0w-xx has to meet the CCS and MRV requirements for -35C and -40C whilst the 5w-xx has to meet the CCS and MRV requirements for -30C and -35C respectively. Ergo, the 0w-xx has better extreme low temperature performance.
 
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Originally Posted By: Oil Changer
No. You are wrong and are ridiculous if you want to argue further.
Originally Posted By: 4wheeldog
The first number, followed by the "W", is the comparative weight (To a single weight oil) when cold. The second number, following the "W" is the weight when hot, (Think 100C) comparable to a single weight of that number, when hot. So, a 5w/30 acts like a 5 weight oil when cold, but as a 30 weight oil when hot. A 30 weight single grade oil is a whole lot thicker at 30 degrees than a 5 weight........But a 5/30 is thinner at 100C than a 5W is at 30 degrees. Read that half a dozen times......It will start to make sense.
I found this to be the best and simplest:
Originally Posted By: OVERKILL
You are completely confused as to how the viscosity system works. The number in FRONT of the W is the "Winter" rating for the oil and is the measure of the oil's RESISTANCE to thicken as the temperature plummets. The number AFTER the W is the SAE grade of the oil as measured at 100C. Both a 0w-20 and a 5w-20 thicken as the temperature drops. This goes for any oil. They are both heavier at 90C than they are at 100C. They are both significantly heavier at 0C than they are at 100C. The difference is that the 0w-xx has to meet the CCS and MRV requirements for -35C and -40C whilst the 5w-xx has to meet the CCS and MRV requirements for -30C and -35C respectively. Ergo, the 0w-xx has better extreme low temperature performance.
I am not sure why you think what I said is different from your position, but there is no point in arguing. All I said was that a 5W acts much like a 5 weight, when both are (very) cold. Do you actually think this is untrue?
 
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