What happens to oil during a warm start?

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Let's use 0-20 Honda Accord V6 as example.

On a cold start, the oil is at 0. As the engine warms up to operating temperature, the oil is now at 20. The oil starts at 0 thin on a cold engine because it needs to be thin, to move faster, squeeze through, to protect all the parts (correct?).

What happens to oil on a cooled down engine and restarted 3 hours later. Would the oil weight be somewhere, let's say at 10 weight?

If it's at 10 weight now, somewhat warm, then how does it able to squeeze through and move around fast enough to protect the engine during a start up?

Thank you.
 
The first and second numbers in an oil's weight have no relation to eachother. Oil is thinner while hot and thicker when cold, a 0w20 vs a 5w20 at cold start up just means that the 0w20 is thinner when cold than the 5w20. A half warm 0w20 isn't at a 10 weight, the 2 numbers aren't directly related, think of them as separate.

Maybe they should have used letters or something on one of the numbers for oil?
 
Hi Cabanalane,

The number before the 0 is a "winter" specification. It is not the weight of the oil. In general, oils become less viscous as the temperatures increase, up to a certain point (then they evaporate and/or sludge, etc.). It certainly can seem confusing, as one would be led to believe that it's a 0-weight (but it actually is 0-winter) when cold and a 20-weight when warm, but the oils actually get thinner as they warm up, not the other way around.
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Someone else can probably explain it better than me.
 
Oil is always thicker as it gets colder. A 0w20 on average will just be less thick than a 5w20 when cold.

A popular 0w20 Mobil 1 AFE 0w20 has a viscosity of 44.8 cSt @ 40C but thins out to 8.7 cSt @100ºC. If you start warm in between those temperatures you would be between those two figure's somewhere.
 
If the temperature where you live never gets below 32 degrees (freezing) it won't matter if you use a 0 weight or a 5 weight.
 
There is some wrong information posted in this thread. Let's take a 0w-20 for example. The 0 does NOT mean it is thinner or that it's a 0w oil. It means that at the proper tempratures it has the flow properties established to be a 0w20. A 0w20 does not mean it is thinner than a 5w20 when cold but at a given temp, usually very cold temps, the 0w20 will flow better. Oil is actually thicker cold than at operating temp.
 
Originally Posted By: simple_gifts
Oil gets thinner as it gets hotter.

That is the guiding principle when considering such matters.

"0 thin" isn't thin in cold temps.
It would be thinner than a straight 30 at the same temps.
 
To quote myself:

Originally Posted By: OVERKILL

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.
 
Overly simplistic and not entirely accurate but close enough for you to understand:

For ALL oils no matter if they are 0w30 or straight-30 weight or 15w50:
Cold=Thick
Hot=Thin

5w_ _ oil will not thicken more than a 5 weight oil when cold.
_w30 oil will not thin more than a 30 weight oil when hot.

Any multi-grade oil is going to flow like ketchup below freezing and flow like cream when hot...

For example:
0w20 is going to flow like runny store brand ketchup when cold and like whole-milk when hot.

15w50 is going to flow like expensive ketchup (where you have to smack the bottle to get it to flow) when cold and flow like heavy whipping cream when hot.
 
Originally Posted By: linksep
Overly simplistic and not entirely accurate but close enough for you to understand:

For ALL oils no matter if they are 0w30 or straight-30 weight or 15w50:
Cold=Thick
Hot=Thin

5w_ _ oil will not thicken more than a 5 weight oil when cold.
_w30 oil will not thin more than a 30 weight oil when hot.

Any multi-grade oil is going to flow like ketchup below freezing and flow like cream when hot...

For example:
0w20 is going to flow like runny store brand ketchup when cold and like whole-milk when hot.

15w50 is going to flow like expensive ketchup (where you have to smack the bottle to get it to flow) when cold and flow like heavy whipping cream when hot.


The number in front of the W does not represent an "SAE 5" when cold. It is its own classification, 5W.
 
Originally Posted By: OVERKILL
The number in front of the W does not represent an "SAE 5" when cold. It is its own classification, 5W.


That's the way I used to think. I used to think a 5W-40 was an SAE 5 when cold, but that was before Garrett jumped all over me and gave me a spankin.
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That's why I said: "Overly simplistic and not entirely accurate..." I'm attempting to convey a general idea; not further confuse the op with the details about how many kilopascals make a nit and how the inverse proportion of nits to coulombs divided by the flux from your capacitor minus one mole times gigawatts equals oil thickness at a given temperature.
 
Originally Posted By: linksep
That's why I said: "Overly simplistic and not entirely accurate..." I'm attempting to convey a general idea; not further confuse the op with the details about how many kilopascals make a nit and how the inverse proportion of nits to coulombs divided by the flux from your capacitor minus one mole times gigawatts equals oil thickness at a given temperature.


But at the same time we don't want to promote the wrong idea either. I'd rather take the extra time necessary for him to understand it properly than over-simplify it and have him explain it incorrectly to somebody else later on
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it takes some time reading about oil to understand many specs, read again + again. here oil 101 etc is a good read, other places like the oilevaluators.com can help. i read wherever i can + continue to learn. oil manufacturers don't want us to know they just want to sell their products $$$$$$
 
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