The viscosity modifiers in motor oil are temperature sensitive additives that cause the oil to thicken as it heats up. At cold temperatures they stay tightly bond up and relatively inactive, so the oil flows thin and easy. As the engine warms up, those modifiers slowly start to expand and do their job.
Why wouldn't a 5w50 be better than a 5w40?
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Correct. You understand now.
A GM engineer back in 2006 or so said viscosity isn't as much of an issue as people think as engines can run on multiple viscosity grades unless the engine has some specific need for a specific viscosity which is pretty rare. Obviously viscosity is very important, but engines are more tolerant than many think.
Like back in the day when every owner's manual had a recommended oil viscosity vs ambient temperature graph. But now CAFE has tried to stop that practice to fool people into using the thinnest oil possible.
Or to thin less.
Just trying to get ahead of the notion that the overall fluid viscosity thickens with increasing temperature.
A lot of recommendations seem to be based on the technology of the time with the lowest common denominator. I remember when my dad was driving a Buick Regal with the 3800 Series II engine. Had a 10W-30 recommendation unless it was cold, where 5W-30 was considered OK. I think it might have had more to do with the volatility of conventional motor oils at the time.
Or connected to the issues GM had with poor VII in the past.
That's the explanation for the masses [of drivers]. If you accept it, fine. If not, you come to BITOG.
CleanSump
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There are some older gentlemen here who have probably done as my Dad did in Nebraska and Minnesota in the '50s and early '60s. He used straight 30 in Spring through Fall and straight 10 in Winter. He also brought the battery into the house when it got really cold, like towards zero and into negatives F.
This was purely for starting issues, not because cars run better on thin oil in Winter and thicker oil in Summer. That's bologna and changing for ambient temps should have gone away when multi-vis oils became widely available. Please don't start an argument or post up anecdotes that don't prove anything.
This was purely for starting issues, not because cars run better on thin oil in Winter and thicker oil in Summer. That's bologna and changing for ambient temps should have gone away when multi-vis oils became widely available. Please don't start an argument or post up anecdotes that don't prove anything.
5w50 is harder to source and a lot more expensive. Its kind of like a boutique viscosity. The 5w40 European and HDEO variety are usually at Walmart or can be ordered from their website.
When we talk about 5w50 is more along the lines of an extreme application like track racing or in a heavily modified engine. 5w40 is usually talked about for turbo engines, hot climates and severe duty applications. I would say for turbos its simply a good idea.
Many European cars like Audi used to spec 5w40 all the time.
When we talk about 5w50 is more along the lines of an extreme application like track racing or in a heavily modified engine. 5w40 is usually talked about for turbo engines, hot climates and severe duty applications. I would say for turbos its simply a good idea.
Many European cars like Audi used to spec 5w40 all the time.
Why 4.2 and not 4.0?
Great results with a straight 30w or 40w in vehicles which dont see climate extremes.
In Les Rudnick's book, that's where he says wear essentially plateaus and becomes non-existent, IIRC.
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Basically the manual says you can put a whole lot of different oils in there without risk of major damage or seizing the engine, but what is best?
People here seem to underestimate the fuel usage issue. There is even a 5w30 and a 5w50 are going to have a huge difference in viscosities(with 5w/50 being considerably more) as it goes through say a warming up cycle say from -10 C to 90 C. Yes the difference in viscosity at 90 C isnt a whole lot different moving from a 30 to 50 oil, but appreciate that unless you are running a thermostat in your oil system(rare as rocking horse.....) the oil is never getting to the desired temp unless you are operating at highway speeds in very warm conditions.
There is also the issue that basically the larger the difference in the numbers ie 5W/50 the more expensive the oil is to make and the shorter time it will last due to the larger amount of viscosity modifiers necessary to make it work eventually breaking down.
Also the engine management systems on cars these days mask the extra drag caused by a thicker oil. Years ago, when driving a carby car with no computer, I changed from a 20w/40 oil to a 20w/50 oil, the hot and cold idle speed for both the 50 oil was noticeably slower than the 40 grade,(tried another brand of 20w/50 and same result) you wont pick up these subtle changes on a modern car as the computer will adjust the idle speed to the preset value.
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no it does not thicken as it gets heated nor does the viscosity increase, its just the degree of thinning is reduced from what happens to a monograde oil.
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basically the numbers represent the end of the temp range viscosities, meaning both oils have the same viscosity at ~100 C.
but it can be guaranteed the 5W oil will remain thicker all the way from -30C up to that temp of 100 C, so its a thicker oil
Not really, as a 0W-20 and 5W-20 are both in the 20 grade range at 100C. The 0W-20 could actually have more viscosity at 100C (a "thick" 20 grade) than a 5W-20. The W grade rating per SAE J300 really only has to do with very cold engine cranking for starting, and the pumpability of the oil to ensure it makes it to the oiling system when very cold.
No that is not guranteed.
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Show the viscosity graph of any 5W-20 versus a 0W-20 graph and tell us at what temp the viscosity of the latter is more than the former? it will be lower for all temps
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