HELP! Can someone please explain the difference between straight and multi vis oils?

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313
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Jefferson, Wisconsin
I have searched on this topic, but I have not really found any answers to my specific questions. I am in a debate with my friend who thinks multi vis oils are bad and just dirty up engines. He thinks a straight 30wt will: Protect far better than a 10w30 Will not cause the engine to get dirty or varnished (he believes that a 10w30 will make an engine dirty becuause there is "something" in it) Will not break down as easily as a 10w30 In winter (Wisconsin... cold) he plans on using a straight 20wt or even just keeping with the 30wt My questions are... what makes a 30wt different than a 10w30? Like... how is a 30wt just a solid 30 and how is a 10w30 two different grades. He uses the straight 30wt Pennzoil in his daily driven 1997 Z28. I know a straight weight oil isnt bad, I just want to prove to him that a multi vis oil is not something to be talking bad about. Thanks guys! [ May 30, 2003, 01:34 AM: Message edited by: Intelman34 ]
 

J

Messages
434
Location
Berkeley
quote:
Originally posted by Intelman34: I have searched on this topic, but I have not really found any answers to my specific questions. I am in a debate with my friend who thinks multi vis oils are bad and just dirty up engines. He thinks a straight 30wt will: Protect far better than a 10w30 Will not cause the engine to get dirty or varnished (he believes that a 10w30 will make an engine dirty becuause there is "something" in it) Will not break down as easily as a 10w30 In winter (Wisconsin... cold) he plans on using a straight 20wt or even just keeping with the 30wt My questions are... what makes a 30wt different than a 10w30? Like... how is a 30wt just a solid 30 and how is a 10w30 two different grades. He uses the straight 30wt Pennzoil in his daily driven 1997 Z28. I know a straight weight oil isnt bad, I just want to prove to him that a multi vis oil is not something to be talking bad about. Thanks guys!
Hi, All oils thicken when they are cold and thin when they are hot. The thickening when cold can be bad enough that oil will not flow and engine wear will result. Unless you live in Florida, your friend's an idiot. Do not buy the stock he recommends either. The "something" in oil is Viscosity Modifiers. These are large polymers which contract when cold and expand when hot. When these expand they help resist flow, and when they contract they do not resist flow well. Resistance to flow is what we call viscosity. When an oil does not resist flow well, it is assigned a low SAE grade. If it does resist flow well, it is assigned a comparatively higher SAE grade (difference has to be large enough since SAE grade is a range). Yes, viscosity modifiers shear and the fragments can contribute to oxidation and thickening. Also, when viscosity modifiers shear their viscosity modifying effect is lost. Your best bet is Mobil 1 10W-30. It will serve your needs well due to lack of viscosity modifiers owing to high intrinsic viscosity index of PAO base stock and narrow spread of 10W-30. [Cheers!] Jae
 

Al

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19,200
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Elizabethtown, Pa
Maybe just to add to what J said. Oils get thick when they get cold ant thin when they get hot. A "multiple viscosity" oil (10W-30) will still be "thicker" when cold but not as "thick" as the straight 30 wt.. So bottom line-your friend is probably causing more wear on startup because the best oil in the world can't lubricate if its not where it needs to be. It's true that a "straight" 30 weight will not break down (thin out) to the extent that a multiple viscosity will but thats really not a big an issue today as it used to be- especially if you change oil at appropriate intervals. Perhaps your friend is living in the past-30 years ago multiple viscosity oils broke down much quicker.
 
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Multi-vis oils, particularly 10W-40, got a bad reputation because of "black death". This was almost complete breakdown of the oil, particularly in high-revving, hot-running European cars. Group I basestocks plus the large amount of VI improver necessary to get 10W to look like 40 led to shearing and oxidation. Older 5W-30 dino oils might have been just as bad. Living in a mild climate, I also used straight 30 until about five years ago. Group II 15W-40 stays in grade for over 6000 miles in my BMW. Synthetic 10W-30 probably does need any VI improver at all.
 
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7,775
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Oklahoma
OK, along those lines, let's say it's summer time, like, now. Temperature doesn't drop below, say 70-ish. Would it be OK for the engine to use a straight weight NOW until fall sets in? My point being this: engine heat PLUS summer heat equals a LOT of heat, period. Oil will thin out more so. Do we really need a 10W-30 now or would it be just as safe to use the straight weight? Like a boat, lot's of people use straight weight, me included, for the summer because we all know that a boat engine will tear the living #ell out of engine oil. The straight weights don't shear as bad. Do we still need the 10W's in the summer? [ May 30, 2003, 11:21 AM: Message edited by: Schmoe ]
 
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8,937
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quote:
Originally posted by Schmoe: OK, along those lines, let's say it's summer time, like, now. Temperature doesn't drop below, say 70-ish. Would it be OK for the engine to use a straight weight NOW until fall sets in? My point being this: engine heat PLUS summer heat equals a LOT of heat, period. Oil will thin out more so. Do we really need a 10W-30 now or would it be just as safe to use the straight weight? Like a boat, lot's of people use straight weight, me included, for the summer because we all know that a boat engine will tear the living #ell out of engine oil. The straight weights don't shear as bad. Do we still need the 10W's in the summer?
In typical summer temps, a straight 30 wt and a 10w30 will be approximately the same viscosity. It's only at colder temps where the 10w30 would be "thinner."
 
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Whoa.....Stop the Truck. What????? I'm getting lost here. Can follow G-Man, but Al, you lost me on that one. Can you elaborate a little more for us non-engineers???? [freaknout]
 

Intelman34

Thread starter
Messages
313
Location
Jefferson, Wisconsin
Hey thanks for all the replies. His Grandpa is the one that set the idea in his head that Multi Vis oils are bad and Straight weight is the only way to go. He went from a 10w30 Mobil 1 to a Pennzoil Dino Straight 30w. Why? Becuase he said his motor made too much noise (LT1 with aftermarket cam, rockers, lifters, springs... its bound to make noise). I just thought it was a shame to switch a car that has seen Mobil 1 its entire life to a Straight 30wt Dino. [I dont know]
 
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EU
Tell your friend that he is correct, actually, but that he must continue to move his throttle lever to the position marked with the little "rabbit" icon when he starts his car. Also, he must change his oil and spark plugs every season or 50 hours of driving, whichever comes first.
 

Al

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19,200
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Elizabethtown, Pa
quote:
Originally posted by G-Man II:
quote:

In typical summer temps, a straight 30 wt and a 10w30 will be approximately the same viscosity. It's only at colder temps where the 10w30 would be "thinner." [/QB]
Well..the viscosity of a 30 wt oil at 68 F is 300 cSt. That equates to a 10 wt oil at 30 F. So there is somewhat of a difference. Loking at another way: If you start your car with 30 wt at 68 F..thats about the same as starting your car (if you had 10W-30) at 30 F. So you will have to decide if thats a good or bad thing. I would still lean to the 10W-30
 
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BC, Canada
YZF150; Thanks for your complement/comment on the 0W30 5W30 thread. I'll try and break up my writing so the paragraphs are not a full page long. Are multi-grades a bad thing? Are single grades better? These are questions frequently asked and there is not a one-size-fits-all answer. Let us look at two and four strode Diesel locomotive engines, an industrial application that I am familiar with. GM's EMD 2-stroke 16-645s and 16-710s (yes that is 11,360 cubic inches) specify a zink free non chlorinated SAE 40 engine oil. I believe that GE's 4400 hp four stroke engines may allow for an optional 20W40 engine oil. Now it appears that GM's Detroit Diesel division alwways specifies either an SAE 30 or SAE40 straight grade engine oil in their 2-stroke engines as well. I think that this straight grade thinking is a little dated and is likely left over from the days when the only way to achieve a multi-grade engine oil was to begin with a light weight base oil then add VI improvers and pour point depressants. GM did not want those improved light weight engine oils in their 2-stroke high output Diesel engines. With the advance in refining technology and the resulting pure and high viscosity base oils, quite typically a straight cut lube will automatically pass a cold flow and cranking test qualifing that oil as a multi-grade. If you look at some Diesel CF-2 oils that have a 40C viscosity of say around 85, a 100C viscosity of about 11.5 and a viscosity index in the ball park of 120, you can bet that that engine oil could easily pass the cold portion tests of 15W that would qualify that oil to be marketed as a 15W30. API's CF-2 states that only straight grades pass as such, but the above 15W30 qualifies because it is not an improved, or manufactured from a light weight LVI base oil. Similarly, people ask why can they not find a straight grade synthetic lubricant. The answer to that question is because of the synthetic's high viscosity index resists the lubricant from increasing its viscosity as the temperature drops better than a LVI fluid, qualifing an engine oil manufactured from a synthetic to pass a multi-viscosity test, or should I say pass more than one SAE viscosity grade's requirements. When one thinks of a multi-grade engine oil manufactured from an improved LVI light weight base lube, using an SAE 10W30 oil for an example, they think of it as an SAE 10W that has enough VI improver to prevent escessive thinning when heated and allowing that oil to pass both the 10W cold flow and cranking viscosity tests and the hot SAE 30 viscosity requirement. When I think of a multi-grade engine oil manufactured from a HVI or VHVI base oil, such as a synthetic, group III, III+, II+, or blends of them, taking a 15W50 as an example. I think of that oil as an SAE 50 engine oil that resists viscosity increses as the temperature drops so that engine oil passes the 15W test in addition to the SAE 50 hot viscosity requirements.
 
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quote:
Originally posted by userfriendly: When one thinks of a multi-grade engine oil manufactured from an improved LVI light weight base lube, using an SAE 10W30 oil for an example, they think of it as an SAE 10W that has enough VI improver to prevent escessive thinning when heated and allowing that oil to pass both the 10W cold flow and cranking viscosity tests and the hot SAE 30 viscosity requirement. When I think of a multi-grade engine oil manufactured from a HVI or VHVI base oil, such as a synthetic, group III, III+, II+, or blends of them, taking a 15W50 as an example. I think of that oil as an SAE 50 engine oil that resists viscosity increses as the temperature drops so that engine oil passes the 15W test in addition to the SAE 50 hot viscosity requirements.
Nope, for ANY multi-weight oil, a relatively thin base oil is used (usually around the Xw rating of the finished product) and VI improvers are used to keep the oil from thinning out at high temps. Of course, if we're talking about synthetics, the VI of the base oil itself may be high enough so the oil will behave like a multi-weight oil with little or no VI improver.
 
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G-man; I thought I covered M.A. by saying "when I think of a......" Some people don't like to call group IIIs or III+ base lubes as synthetics. I think that many of the better single grade engine oils manufactured from group II or II+ will meet multi grade requirements such as 25W40, 20W30, 15W20, 15W30, and other non-mainstream or un-used SAE grades. Some group III could be added to a II brew to bring the cold flow numbers down and allow the multi-grade classification to be brought down another notch. There must be 100 posts that imply or declare that group IIIs are not synthetics on this site, so we are not talking a semi-synthetic or synthetic blend here. I don't care if my CF-2 SAE 30 doesn't have 15W30 written on the side of the pail. Its a group II multi-grade to me and that is all that counts. If you want your oil to be a 10W30, I'm under the impression that a 25% substitution of a group III base stock instead of the group II might do the trick without VI improvers. I believe that the multi-grade oil that I am referring to is not in the same league as the $0.69 cent K-Mart special. Please note the CYA phrases as "I believe, I'm under the impression, I don't care, Its a multi grade to me, might, could, I think, and all that matters (to me) are my opinions and all though they may not be factual or correct....It does not matter to me. Now I have to learn how to add one of those Icons, after all they are the only reason I read through all these threads. [Smile]
 
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quote:
Originally posted by userfriendly: G-man; I thought I covered M.A. by saying "when I think of a......" Some people don't like to call group IIIs or III+ base lubes as synthetics. I think that many of the better single grade engine oils manufactured from group II or II+ will meet multi grade requirements such as 25W40, 20W30, 15W20, 15W30, and other non-mainstream or un-used SAE grades.
Well, since a Group II+ base will have a max VI of 119, I think you're wrong. [Wink] Adding a little bit of Group III (with a typical VI of 130) to that isn't going to give you a motor oil with a finished VI of 140 (the typical VI of a non-syn 10w30). Some VI improver will be needed.
 
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G-MAN II+; I was thinking of an oil like Mobil's Delvac 1330, or closer to town Pet-Can's Duron 30 as an example of the above theory of a straight grade engine oil meeting a cold cranking and flow viscosity test that would qualify them as multi-grade engine oils. Here are the basic viscosity typicals posted on their web sites: Pet-Can Duron 30: 40c.....83 100C....11.2 VI....123 flash..249C pour ..-36C Mobil's Delvac 1330 40C....90 100C...11.5 VI....117 flash...250C pour....-30C I hope this post does not un-thread. Do you think that these two oils could pass a 15W, 20W 0r 25W cold cranking and flow test?
 
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8,937
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quote:
Originally posted by userfriendly: Do you think that these two oils could pass a 15W, 20W 0r 25W cold cranking and flow test?
No. The VIs of these oils are two low. They would be too thick to meet the cold cranking and cold pumping specs for a 15w or 20w oil. (As far as I know, there is no 25w.)
 
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3,216
Location
BC, Canada
G-MAN II; I've asked the same question three times, but in different ways each time. You have answered much in the same way each time, meaning your are pretty well set in your conviction that a high VI is required for a lubricant to pass a mluti-grade test. Read the following and let me know if I have this correct. 1. An engine oil that is sold as a multi-grade must pass the viscosity requirements of more than one SAE grade. 2. An engine oil that is manufactured from a high VI base oil such as a PAO synthetic, Group III, III+ ect, may pass a multi-grade viscosity test requirement without VI improvers added to the formula. 3. A lubricant that does not have a high viscosity index will thicken excessivly when chilled. That thickening, or excessivly increased viscosity, will prevent that lubricant in the application of an engine oil, from passing the cold flow and cranking tests for a "W" rating in addition to its "100C" SAE grade. 4. An engine oil that is manufactured from a low VI base stock, must start with a relitivly thin or light base fluid then have VI improvers added to the brew to prevent that lubricant from excessive thinning when heated. Just to make sure we are both on the same page GMII, is there anything I said in paragraphs #1, 2,3, or 4 that you do not agree with or would like to add to? [Smile]
 
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I'd change your #1 item to say that the oil must pass a specific cold viscosity test and a hot viscosity test. Any straight grade oil has not had the cold vis test (at least not for public consumption). Ken
 
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