Possibly common questions on oil

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I've done some poking around this forum and found these questions popping up often. Frankly, I can't get straight answers on them. This may be a futile attempt to get answers but I thought I'd try... 1) Does oil color indicate anything about engine health at the end of the OCI? Common sense dictates if the oil is as clear as when it was put in that the engine is either spotless or the oil isn't cleaning the mess that is in there. 2) If the additive packages in oils control the cleaning of the engine, why are synthetics generally considered better at this? Is it simply that the higher price justifies more additives for synthetic oils? 3) Since each oil will be different from the next, why would anyone recommend a general synthetic over a general conventional? Wouldn't the best conventional oil beat out the worst synthetic in terms of performance? (this is assuming synthetics are generally considered superior to conventional oils - which I realize is controversial around here) 4) Do synthetic oils give a film that stays on the metal parts? Is this why startups are supposedly easier with synthetics? Why don't conventional oils do this? 5) Does an oil type like 5W30 imply the oil is thinner at lower temps and thicker at high temps? Or is it the other way around? Thanks for the info.
 
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1. Not really. 2. Yes, most synthetics have a better additive pack. For example, M1 has more detergents than Mobil Clean 5000 (per their website). I have yet to hear of a "premium dino" that would have the higher level of cleaning in a cheaper base stock. 3. Basically the better additive pack and cold weather performance for me. Perhaps the best conventional would be better than than a worst synthetic, but that's not really fair. The real question is if PP is better than YBP, or if M1 is better than clean 5000, or if SynPower is better than regular Valvoline. They are. 4. Both (any) oil will leave a film. Synthetics flow better when cold, so they will reach full flow more quickly. 5. A 5w-30 still gets thinner as it gets warmer. It just changes thickness more slowly than a 30 weight. So at temp it's the same thickness as a 30 would be at temp. At freezing, it's the same thickness as a 5 would be at freezing.
 
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 Originally Posted By: mozart
1) Does oil color indicate anything about engine health at the end of the OCI? Common sense dictates if the oil is as clear as when it was put in that the engine is either spotless or the oil isn't cleaning the mess that is in there.
Correct. That's why you can't really tell just from looking at it. For someone who claims to be a newbie, you're a sight ahead of a lot of people. ;\)
 Originally Posted By: mozart
2) If the additive packages in oils control the cleaning of the engine, why are synthetics generally considered better at this? Is it simply that the higher price justifies more additives for synthetic oils?
First, almost all synthetics resist deposit formation better because they don't break down as easily. Second, some synthetics (Group V) consist of polar molecules that break down and dissolve certain kinds of gunk all on their own. Synthetics do usually get the better additive packs, although modern conventionals often have very good additive packs as well.
 Originally Posted By: mozart
3) Since each oil will be different from the next, why would anyone recommend a general synthetic over a general conventional? Wouldn't the best conventional oil beat out the worst synthetic in terms of performance? (this is assuming synthetics are generally considered superior to conventional oils - which I realize is controversial around here)
Depends -- and you'll get lots of opinions on this. As far as I can tell, the general consensus is this: when you're comparing a basic synthetic to a good conventional, the only real advantage to the synthetic is resistance to extreme temperatures. Other than that, the real benefit of the conventional will be cost: it's not better, but it'll be much cheaper.
 Originally Posted By: mozart
4) Do synthetic oils give a film that stays on the metal parts? Is this why startups are supposedly easier with synthetics? Why don't conventional oils do this?
Some do (Group V). Some would actually slip off faster than conventionals (Group IV) unless they have the right additives (which, to be fair, most or all of them do). The real benefit of a synthetic on a cold start is that it flows better at low temperatures and is therefore easier to pump.
 Originally Posted By: mozart
5) Does an oil type like 5W30 imply the oil is thinner at lower temps and thicker at high temps? Or is it the other way around?
All oils are thicker when cold and thinner when hot. The spread indicates how big the difference is. As an example, let's take a straight 30 weight, a 10w-30, a 5w-30, and a 0w-30, which are all similarly formulated and about the same viscosity when hot. Let's say they're all 10 cSt. Now, let's cool them down to room temperature. They all thicken, but by different amounts: now the 0w-30 is 65 cSt, the 5w-30 is 75 cSt, the 10w-30 is 90 cSt, and the straight 30 weight is 110 cSt. Now, stick them in the freezer. The 0w-30 still flows, the 5w-30 is more like honey, the 10w-30 barely moves, and the straight 30 weight is gel. These are TOTALLY random numbers, and remember that this is "all else equal". In reality the relationship isn't that clean and there are some exceptions -- e.g. some synthetic straight-30s pump just fine in temperatures that would gel a conventional 10w-30. But, that's the general idea about multi-grade viscosity ratings.
 
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The biggest concept for most oil newbies to hurdle is the cold viscosity numbers. If the car calls for a 10W-30, folks often ask, "so isn't a 5W-30 too thin". The answer is almost undoubtedly "no". For the longest time, I thought oil thinned when it gets hot, but it really helped me to think about it from the other direction, and think that oil thickens when cooled. So even though 5W-30 is "thinner" than 10W-30 when cold, either one is still WAY thicker than they would be at operating temperature, and likely WAY thicker than really desired. I suppose this is why 0W-xx oils are becoming preferred...they don't thicken as severely when cooled. I suppose the "ideal" oil would be something like a -10W-30, huh? Something that's ABOUT as thick at room temperature as it is at operating temperature.
 

mozart

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So for 5W30, is the "5" or the "30" the Winter weight? In other words, is a high number a thicker liquid?
 
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5w is winter rating (not weight). Higher means it thickens more when cold. 30 is the weight, as measured at 100 degrees C. Higher means thicker.
 
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 Originally Posted By: mozart
So for 5W30, is the "5" or the "30" the Winter weight? In other words, is a high number a thicker liquid?
The 5W is the viscosity grade when measured cold (at 32*F I think). The 30 is the viscosity grade when measured hot (at 212*F I think). It gets confusing because the lower number is for the colder grades, so at first, you'd think the oil was thinner when cold than when warm. But it's simply stating that, when cold, the oil is acting like a 5 grade oil, and when warm, the oil is acting like a 30 grade oil. When cold, even a 5 grade oil is WAY thicker than a 30 grade oil is when hot.
 
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Once I finally grasped this concept I got to thinking. One can only imagine what a 15W-50 or a 20W50 must be like on a 0*F day being forced through the engine bearings, slllllllllooooooowwwwly. Especially in an engine designed to run on 5W20 or 5W30. Hopefully residual oil stays put long enough to keep them protected until proper flow is established.
 
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Pablo, I don't understand. The J300 table shows the viscosity of a 5W oil as 3.8 cSt at 100*C (212*F). But a 5W-30 oil doesn't have a viscosity of 3.8 cSt at 100*C; its viscosity is closer to 10-11 cSt (as a 30 grade should be at that temperature). I guess I don't understand why the statement "the 5W is the viscosity grade when measured cold" is not accurate. Should I have said something like, "the 5W is the ~equivalent~ viscosity grade when measured cold"?
 
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 Quote:
3) Since each oil will be different from the next, why would anyone recommend a general synthetic over a general conventional? Wouldn't the best conventional oil beat out the worst synthetic in terms of performance? (this is assuming synthetics are generally considered superior to conventional oils - which I realize is controversial around here)
My stance has always been that synthetic is better for long OCIs. When used for 5,000 mile OCI, a conventional and synthetic will arguably put out low wear numbers. It's when you increase the interval that synthetics shine...also in extreme cold. By extreme, I mean -20F. Not a measly 32F. Plenty of folks use dino 5w30 in Canadian winters and the engines are fine. IMHO, if you use synthetic for 5,000 mile OCIs you are just wasting money. Check out the UOA section, and how many people dump their synthetics out before 5,000 miles. If you don't feel you have the confidence to run oil longer than 5k, use a dino.
 
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 Originally Posted By: Jason Adcock
Pablo, I don't understand. The J300 table shows the viscosity of a 5W oil as 3.8 cSt at 100*C (212*F). But a 5W-30 oil doesn't have a viscosity of 3.8 cSt at 100*C; its viscosity is closer to 10-11 cSt (as a 30 grade should be at that temperature).
5W is 3.8 min.....but that's just a 5W oil. Not too many of those on the market. The table can be a little confusing I guess. For 5W-30 look at the 5W row (first two columns) and 30 row 3 and 4 columns. http://www.infineum.com/information/api-viscosity-2004.html
 Originally Posted By: Jason Adcock
I guess I don't understand why the statement "the 5W is the viscosity grade when measured cold" is not accurate. Should I have said something like, "the 5W is the ~equivalent~ viscosity grade when measured cold"?
Well nothing wrong with that part of the statement per se, but again look at the columns.
 
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