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I've heard more than once that running 10w-40 is bad and can cause problems, and have since quit using it. But I've never heard any real reasons why or what it does. Why is it not good to run this oil?
It would take me a bit to find the web pages, but there were two pages I read a couple years back that mentioned 10W40 problems. Keep in mind, I am not an oil expert and only know what I have read and have seen enough respectable articles to keep me away from 10W40 oils. Besides, there are so many other options, why risk it?
One web page was comparing oils from the different brands and showing the levels of additives etc and how they flowed etc. The author mentioned that he specifically left out the 10W40 oils "for known reasons". He didn't specify the reasons other than to say some engine manufacturers will void the warranty if 10W40 is used. I have read this statement in several places including the manual for my Generac engine and a Tecumseh engine, they both state "Warranty is void if 10W40 oil is used." I have also read that Volvo has the same statement.
The other website discussed what the Europeans call Black Death. Is you use 10W40 oil, it will in effect burn after some time and "coke" up the engine, ie clog it up with carbon residue.
The explanation of this problem has been on a few web sites and what they say is that the "Rule of Thumb" is to not use any dino based oil with a viscosity spread of 30 or more. Synthetics are exempt from this rule since their base oil has a much higher "burning" point.
Back to dino oils... The multi viscosity oils get their spread by using viscosity index improvers(VII). The oils start out with what ever base they have, ie 10W oil has a base oil that flows like 10 weight oil in winter. The oil companies add VII's to the base oil to get the spread they desire, ie 10W40 oil starts with a 10W and adds enough VII to get the oil to flow at high temperatures like a 40 weight oil. The way this works is the VII's are essentially polymers that stay "coiled up" at low temperatures thus allowing the thin 10W base to flow. At higher temperatures a 10W base would be too thin. The VII's step in to the rescue. The VII's uncoil at temperature and make the oil act thicker and flow properly for that weight at high temperature.
All good stuff except remember, I mentioned that VII's are essentially polymers, AKA plastics. The more polymers added to the oil, the less real oil you have per quart. The polymers do not lubricate as well as the oil and they can over heat and burn. The resulting overheating oil and burned VII's cause deposits to collect in the oil passages over time, eventually leading to oil starvation, very bad for engines. The Europeans had engines full of black gunk so they called it Black Death.
If you change oil religiously at short intervals, say 3,000 or less and if you don't drive in hot conditions, I suspect you won't have a problem with 10W40. But like I said why risk it when there are lots of safe alternatives?
Now you might question the 30 point spread rule and say "But wait, 20W50 violates the rule too". Yes, but not a problem. The base oil remember was a 20W, which has a higher tolerance to burning than 10W base. So this problems has not been seen with 20W50 oils.
In a nutshell, there has been a lot of evidence that 10W40 oils can "coke up" and cause premature failure, while the record for less than 30 point spread oils is good. Admittedly it is possible that the oil manufacturers have changed the formula and maybe the 10W40 issue is dead. But I have noticed that there are not as many 10W40 oils as there are 5W30, 15W30, 20W50, even 0W30, so maybe the oil companies are shying away from potential problems or perhaps market "superstition" has driven demand down.
In any case even if things have changed and the "facts" are wrong, what is the harm in going to one of the more popular weights. Better yet, I use synthetics in everything and don't worry about temperatures.
Just info I have read and hopefully put down in a reasonable summary.
I have put over a half million miles on several engines one 206,000 while using 10W40. I personally think it is BS. The newer engines want 5W30, use it if it is recommended. 10W30 is good also. You are talking about a blend of different oil thicknesses 5 being thinner, 40 being thicker. One is for cold starts and the other for hot climates, when the heat thins the oil further.
I have started using 10W30, but Iam not afraid of 10W40.
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Found one of the websites. http://rconcepts.com/beard/dragnet/drag/oilinfo.html
I do not know who this Ed Hackett guy is but he has written a lot of articles including about oil. So I assume(make and A$$ of u and me) he has better credentials than I do, and besides I have seen similar, material elsewhere. Some intersting info there on the various brands, although info may be dated. In any case here are a few snips.
Read and interpret for your self.
For your reading entertainment, and snip...Multi viscosity oils work like this: Polymers are added to a light base(5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot. Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. In the winter base your decision on the lowest temperature you will encounter, in the summer, the highest temperature you expect. The polymers can shear and burn forming deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers(synthetics excluded) to achieve that range. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best. Very few manufactures recommend 10W-40 any more, and some threaten to void warranties if it is used. It was not included in this article for that reason. 20W-50 is the same 30 point spread, but because it starts with a heavier base it requires less viscosity index improvers (polymers) to do the job.
Uh, BS!!! So straight 30 weight should lubricate the best? HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA
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