Why do some people say 0W20 can cause more leaks compared to a 5W20?

Jackson_Slugger

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You’d have a lot more chance of making a difference with a 30 or 40-grade.
A difference of what? Mobil 1 HM 5W-20 sealed weeping leaks on my father's Taurus almost instantly...I've also seen full syn 10W-30 gush out of engines...

But feel free to explain how an oil with a significant amount of ester like Mobil 1 HM or EP high mileage is going to be any worse than a generic 5W-30 due to being a 20W...
 
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Sorry if this has already been discussed but my car is spec'd for 5w20 but here in Canada we get horrible winters as cold as -40 fahrenheit some days so a 0W20 obvs wouldn't hurt. I was doing some reading and seems like I read some posts about some people say "if you run 0W20, watch out for leaks"
I just dont understand how thats possible unless I am misinformed. A 0W oil will be less viscous compared to a 5W oil at a cold temperature, whatever the benchmark cold temp is. And then the second number is at operating temp and at this case they are the same.

For example, lets say its cold out. then a 5w20 would be viscous and as the temps heat up in the engine, it would slowly heat up and become less viscous until it reaches that 20 grade. However when a 5W20 is heating up, it would obviously be less viscous compared to a 0W20 that is cold right? In that case, If a 0W20 was said to cause leaks then in this same scenario wouldn't the 5w20 cause that same leak when it is warming up/engine is getting to operating temp? or am i missing something here


thanks!
You stated a valid reason to run 0w20 over 5w20. So I say, run 0w20. This debate about leaking oil originated from changing from conventional to synthetic. The reason that was to be the case is that synthetics were to have better cleaning abilities that it could clean out dirt that was concealing a leak. You haven't mentioned age of vehicle or what oil you were using previously. If you were using a synthetic 5w20, then you likely won't get a leak. Being in Canada, I say, just use the 0w20, and if you get a leak, fix it,
 
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Many times I've thought I knew something and it turned out I misunderstood. Happens more often than I'd like to admit. Sometimes it is right here on this forum. It's a great place to get corrected and to be educated. So no harm, no foul.

I wish I'd read the other corrections before I posted. And I wish this forum offered a delete option. Not sure why it doesn't. If it did, I'd delete my post right now.
 

4WD

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Best definition of "leak". I'm tired of people saying oil cause leaks. Oil might show it, it might reveal it, but in the vast majority of cases, it doesn't cause it. Causation vs correlation is something that should be taught in school, starting in 5th grade. But that ain't not never gonna happen.
Like infamous wet seals … have had them leave oil on surfaces for years … but nothing on the concrete …
 
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Many times I've thought I knew something and it turned out I misunderstood. Happens more often than I'd like to admit. Sometimes it is right here on this forum. It's a great place to get corrected and to be educated. So no harm, no foul.

I wish I'd read the other corrections before I posted. And I wish this forum offered a delete option. Not sure why it doesn't. If it did, I'd delete my post right now.


One way to delete is to edit the post. Erase the comment and type DELETED or whatever you prefer.

I find that previous comments I started on but didn’t post end up still in the box. I will erase and put a couple of .. to satisfy the software.
 
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What on earth are you talking about? Oil does not thicken as it heats up, that would defy the laws of physics.

And as noted unless it is extremely cold the oil with the 5W winter rating is not necessarily thinner than the one with the 0W rating. And even if it is both are very thick at lower temperatures.
Actually, isn't that what a VI does to a multigrade oil? It's a 0 at low temp, but as temps rise, the Viscosity Index component increases the RELETIVE viscosity of the oil from the behavior of a 0 to that of a 20.

The actual viscosity is still lower than it would be at the lower temperature, but is HIGHER than it would be if it were a straight 0 oil.
 
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sorry for bad english, i mean't find leaks. not cause.
I figured that's what you meant but seriously ( no bearing on your post or this thread) in my teachings for ML-1&2 and CLS over the years, I encounter many people who do really believe that 'somehow" the oil ( specifically a synthetic) did somehow "cause" a leak.

I get hit with it all the time
 
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Best definition of "leak". I'm tired of people saying oil cause leaks. Oil might show it, it might reveal it, but in the vast majority of cases, it doesn't cause it. Causation vs correlation is something that should be taught in school, starting in 5th grade. But that ain't not never gonna happen.
Grammar too! 😂
 
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side topic, is the reason people say synthetic finds more leaks compared to conventional due to additives and cleaning ability? or is that a old wives tale as well? if we are comparing 5w30 with 5w30 then obvs the viscosity would be similar to be called a 5w30
 
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Actually, isn't that what a VI does to a multigrade oil? It's a 0 at low temp, but as temps rise, the Viscosity Index component increases the RELETIVE viscosity of the oil from the behavior of a 0 to that of a 20.

The actual viscosity is still lower than it would be at the lower temperature, but is HIGHER than it would be if it were a straight 0 oil.
No, there are no “0” oils and that’s not what the winter rating means.
 
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The terms are confusing.
It's worth noting that mamy 10w30 are thinner than 0w40 or even most 0w30 at kv⁴⁰ & kv¹⁰⁰
However the 0W oils supposedly have better pumpability at freezing temps.
 
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The terms are confusing.
It's worth noting that mamy 10w30 are thinner than 0w40 or even most 0w30 at kv⁴⁰ & kv¹⁰⁰
However the 0W oils supposedly have better pumpability at freezing temps.
Of course they are, one is a 30-grade and one is a 40-grade. 30-grade oils are thinner than 40-grade oils.

And “freezing” is relative. In general an oil with a 0W winter rating is only guaranteed to be thinner than an oil with a 5W winter rating at temperatures somewhere around -35F and below.
 
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Of course they are, one is a 30-grade and one is a 40-grade. 30-grade oils are thinner than 40-grade oils.

And “freezing” is relative. In general an oil with a 0W winter rating is only guaranteed to be thinner than an oil with a 5W winter rating at temperatures somewhere around -35F and below.
My point is that the winter "W" terminology can be confusing as many assume a lower W number correlates to a lower viscosity. Hence my point that there are 5w30 & 10w30 that are less viscous than 0w30 at the measured Kv
 
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side topic, is the reason people say synthetic finds more leaks compared to conventional due to additives and cleaning ability? or is that a old wives tale as well? if we are comparing 5w30 with 5w30 then obvs the viscosity would be similar to be called a 5w30

Old wives tale. There could have been some poorly blended synthetic PCMOs in the very past (e.g. 1970s), e.g. majority PAO content without appropriate Group I/II or ester content to make it fully compatible with very most seal material. Secondly, seal material changed over the decades (e.g. from rubber, felt etc. to EPDM). Unlike today (say from 1980s up) some of the seals used in the 1960s weren't fully compatible with later (first synthetic) oil compositions. Maybe that's the origin of that old wives tale. Just speculation of course, but it would explain it. Get a proper synthetic with reputable certifications and ideally current manufacturer approvals and there's no increased risk for leaking. All the majors test their products for seal compatibility.
 
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What on earth are you talking about? Oil does not thicken as it heats up, that would defy the laws of physics.

And as noted unless it is extremely cold the oil with the 5W winter rating is not necessarily thinner than the one with the 0W rating. And even if it is both are very thick at lower temperatures.
Doesn't thicken, starts behaving as a 20w
 
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from my experience, going down on the winter rating can cause / increase engine oil consumption.

If you have run good quality FS from the begining, engine leak should not be caused by swithing to 0w

My toyota recommended viscocity is 5w30 but I have run mobil 1 0w40 since new with no leaks nor oil consumption rom the engine at close to 90k miles (touch wood!)
 
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