Oil weight when cold vs hot

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Curious why oil seems thinner when hot/warm vs thicker at room temp? Example: 5w30 pours thicker at room temp that at running temp.
 
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Magic. Sorry, could not resist. Stealing from wikiedia as it was "easier" A molecular view of liquids can be used for a qualitative picture of the process of decrease in the shear (or bulk) viscosity of a simple fluid with temperature. As the temperature increases, the time of interaction between neighbouring molecules of a liquid decreases because of the increased velocities of individual molecules. The macroscopic effect is that the intermolecular force appears to decrease and so does the bulk (or shear) viscosity. Basically molecules react faster when warm because the molecules themselves are more free to move
 
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It sounds like stygz is still hanging on to the old myth that engine oils are thin 5 wt when cold but thicken to 30 wt when hot. They are measured hot & cold on different scales. 5W earns its designation by being tested at -30°C & -35°C. 30 weight earns its designation by being tested at 100°C. So an oil that meets the thickness spec at those frigid temperatures and meets the thinness spec at that hot temperature can wear the 5W-30 viscosity grade label. (The W means winter, not weight.)
 

stygz

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Looking at the table on oil 102 I wonder what the thickness of 5w30 is at 75 degrees? Split the difference of 10w and 0w? I can now see how a 0w30 may be more bennifcial upon start up.... Not even factoring a subzero temp
 

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Originally Posted By: Ken2
It sounds like stygz is still hanging on to the old myth that engine oils are thin 5 wt when cold but thicken to 30 wt when hot. They are measured hot & cold on different scales. 5W earns its designation by being tested at -30°C & -35°C. 30 weight earns its designation by being tested at 100°C. So an oil that meets the thickness spec at those frigid temperatures and meets the thinness spec at that hot temperature can wear the 5W-30 viscosity grade label. (The W means winter, not weight.)
Actually I think it was me not knowing there is a difference between Viscosity and thickness
 
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I think the confusion is when neophytes and other pseudo-experts in press and other forums state that "multi-viscosity oil, like a 5w-30 will be thinner when cold to help cranking and speed oil flow to critical engine parts". They really mean (I HOPE) that a 5W-30 is multi-season oil is thinner than a SAE30 monograde at cold temps. All Multivis are less viscous as they are warmed.
 
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Originally Posted By: stygz
Curious why oil seems thinner when hot/warm vs thicker at room temp?
Same reason why honey barely flows when you pull it out of the fridge, but flows freely when you heat it up in a pan on the stove.
 

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Originally Posted By: EdwardC
Check it out again, should help answer some questions: http://www.bobistheoilguy.com/motor-oil-101/
Good read. I actually think it was a different article that I had read before. It has me second guessing a couple choices 1. Consider using a 0w30 instead of 5w30 in my vehicles 2. My triumph motorcycle manual recommends 10w40 or 10w50. My dealer exclusively stocks the 10w50 however the manual throws out the suggestion of Castrol power 10w40. I wonder if the dealers say to use the 10w50 because it usually requires a visit to the dealer vs a stop at Autozone. It would seem after reading these articles a 10w40 seems like it would be better. FYI I do not take my bike to the track, just commuting and ripping back roads. I intend to stay with castrol power as the price cannot be beat from Amazon.
 
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I keep saying: -The 2nd number (the one after the "w") is the oil grade, and reflects viscosity at operating temperature. (10w30 is a 30-wt at operating temp, so is 0w30 and 5w30 and SAE30, they're all nominally the same in your engine when its at full operating temperature, barring product-to-product variation and tolerances in the spec.) -The first number is a rough measure of how much the oil thickens as it cools down. 10w30 nominally thickens more than 5w30, and 5w30 thickens more than 0w30. But the temperature at which that first number is determined is REALLY low, so if (for example) it only gets down to 10deg F in your area, a 5w30 and 0w30 may do exactly the same thing and the 0w30 would only have an advantage if it kept getting colder. -It is NOT a case of "its a 10 weight when its cold and a 30 weight when its hot."
 
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I believe your triumph has a wet clutch. I think that the oil viscosity has a larger effect on the shifting feel. I think either oil will work for you, but it's possible that as the 10W40 shears down to a thinner weight, you'll notice poor shifting. The 10W50 might have further to go to shear to a point that you notice. Rotella T6 5W40 and Triple T 15W40 are popular options for bikes, especially the 15W40. It is JASO MA for wet clutches too.
 
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Originally Posted By: Quattro Pete
Originally Posted By: stygz
Curious why oil seems thinner when hot/warm vs thicker at room temp?
Same reason why honey barely flows when you pull it out of the fridge, but flows freely when you heat it up in a pan on the stove.
Reminds me of home ( Albuquerque) where warm sopapillas are eaten with plenty of honey. Heavenly delight I haven't experienced in a number of years. Plan to have those sopapillas with honey some year soon.
 

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Originally Posted By: EdwardC
I believe your triumph has a wet clutch. I think that the oil viscosity has a larger effect on the shifting feel. I think either oil will work for you, but it's possible that as the 10W40 shears down to a thinner weight, you'll notice poor shifting. The 10W50 might have further to go to shear to a point that you notice. Rotella T6 5W40 and Triple T 15W40 are popular options for bikes, especially the 15W40. It is JASO MA for wet clutches too.
It could be because of shearing as they recommend a 6k OCI
 

stygz

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Originally Posted By: 440Magnum
I keep saying: -The 2nd number (the one after the "w") is the oil grade, and reflects viscosity at operating temperature. (10w30 is a 30-wt at operating temp, so is 0w30 and 5w30 and SAE30, they're all nominally the same in your engine when its at full operating temperature, barring product-to-product variation and tolerances in the spec.) -The first number is a rough measure of how much the oil thickens as it cools down. 10w30 nominally thickens more than 5w30, and 5w30 thickens more than 0w30. But the temperature at which that first number is determined is REALLY low, so if (for example) it only gets down to 10deg F in your area, a 5w30 and 0w30 may do exactly the same thing and the 0w30 would only have an advantage if it kept getting colder. -It is NOT a case of "its a 10 weight when its cold and a 30 weight when its hot."
If my summer temps were to get down to 70 degrees at night a 0w30 and a 5w30 would have the thickness at start up? Considering the 0w30 for start up protection.
 
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Originally Posted By: stygz
Considering the 0w30 for start up protection.
Maybe if you lived somewhere up north. In Georgia, it's unlikely to make much of a difference, IMO.
 
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Originally Posted By: ARCOgraphite
Have you not read the oil 101 basics yet?
They guy says to run 0W20 in a Lamborghini. I don't know if he knows what he's talking about.
 
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He knows his driving condition and it is mostly short distance at city limit speed of less than 50 MPH, with that condition the 0W20 oil is barely get to 150-160F and at that temperature it is still too thick for any engine. I use M1 0W20, PP 5W20 ... in my E430, the recommended grade is M1 0W40 without problem, actually the engine is running quieter and throttle response is much quicker. The main reason is the car is usually driven less than 10-15 miles per trip.
 
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