- Apr 18, 2006
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Something hattech-v pointed out, and hopefully everyone can read and correct this if I'm wrong, and add some information that they know of.
When I first thought about engine oils and the numbers.. I got confused.. an oil is an oil is an oil.. or so I thought.
So.. I endeavoured to research on the matter (long time ago..)
I don't exactly remember the details but this is what the numbers mean.
SAE5w30
What this means is that the oil is the thickness of 30 (the unit name escapes me, it's some obsure term made up by the Society of Automotive Engineers, a.k.a. Society of Acronym Enthusiasts) Edit: I just remembered.. Viscosity!
So a SAE5w30 oil at 100 degrees C is having the thickness of 30, and as it is heated up, it becomes thinner..
Remember the cooking oil? notice how easily it flows once it's hot? (if you're not a cook, ask your wife/live-in girlfriend/concubine!)
Or if you're more involved in cars, take the grease and burn it.. what happens? It melts into oil, right? Grease is oil.. a VERY THICK oil.. how much SAE weight.. I don't know! But probably some huge number... and it's W rating is probably high as well, as it doesn't take a very high temperature to melt.
Same thing with engine oil... A SAE5w30 oil will become thinner than 30 when the engine is running over 100 degrees C, so that's about it..
Thin oil = less protection, so you can see why keeping the oil thick at higher temps is important.
So what's the 5w mean?
The 5w is not the weight.. it has nothing to do with the oil, but rather, it shows how resistant the oil is to become thin at higher temperatures. All oils become thin as they are heated up, and the 5w sort of represents how well the fuel can help keep the oil thick at higher temperatures over 100 degrees C
So a SAE5w30 oil will thin out less than a SAE10w30 oil if you're cooking them in the engine at more than 100 degrees C. So a 5w30 oil is better as the temperature gets hotter.. As to the actual weight at certain heat temperatures.. I don't know.. I never bothered to research!
That's why the SAE0w20 is considered better than SAE5w30, and SAE5w30 is considered better than SAE10w30..
As an example, consider this FABRICATED SCENARIO
If SAE0w20 is heated up to 200 degrees C, the weight of the oil is still SAE20(I'm just putting a random number to illustrate the point, so don't take the number as a definite answer) It should decrease, but I don't know by how much exactly, but it will be less than an oil that has a 5w or 10w rating.
Now SAE5w30 at 200 degrees C, may suffer more, and go down to SAE18 (yet another random number. and at maybe at 300 degrees C, it may be even thinner than SAE0w20 at 300 degrees C. Maybe it will be thin like water, yet the 0w20 will still be like oil, keeping its lubrication properties
And the SAE10w30 at 200 degrees C, even worse, going down to SAE15 or so... and probably will become thin like water even at even earlier temps than 300 degrees C
That's why you find an OLD hot engine starts easier than when cold.. it's because the oil is thinned out enough that there's less resistance for the oil to flow. Since there's probably sludge stuck on the oil passages, the passages are more restrictive, so a thinner oil will flow better!
A possible solution.. NOT!
Why not thicker oils then? if we put in SAE15w100, shouldn't that help protect the engine? Maybe the oil would thin out to SAE30 when heated up?
Thing is, a SAE100 oil would probably look like grease when it's cold, and you can guess how hard is it for the engine to push that grease into narrow oil passages in the engine. Starting up the engine would be a nightmare! That's why some cars can use thicker oils and some cars don't...
Remember that honda engine uses the engine oil to push the dowels to engage the secondary lobe (that's VTEC for you) so that's why honda engine seems to need thinner oils than say, a proton car, and why some people like SAE5w30 in their car rather than the honda recommended SAE10w40, or why people run 0w20 oils on *some* racecars.
A kancil requires even thinner oil because the engine is so small, you can guess how small the oil passages are.
You can probably run thicker oils like SAE15-50, but the engine would probably be harder to start in the mornings.
So that's about it..
The 0w,5w,10w rating is obtained by adding additives to the motor oil.. so more powerful additives are in 0w, a bit less on 5w, and even less on 10w.. That why some mechanics say 0w and 5w is considered synthetic, and 10w is considered semi-synthetic, and a 15w oil is considered non-synthetic..
If you want more info.. you can google up the term "Motor Oil Bible"... it's in PDF format, and the info within is quite accurate when I asked an engineer friend about stuff I learned from it.
I've read it a few years back, so I don't remember exactly what it said.
When I first thought about engine oils and the numbers.. I got confused.. an oil is an oil is an oil.. or so I thought.
So.. I endeavoured to research on the matter (long time ago..)
I don't exactly remember the details but this is what the numbers mean.
SAE5w30
What this means is that the oil is the thickness of 30 (the unit name escapes me, it's some obsure term made up by the Society of Automotive Engineers, a.k.a. Society of Acronym Enthusiasts) Edit: I just remembered.. Viscosity!
So a SAE5w30 oil at 100 degrees C is having the thickness of 30, and as it is heated up, it becomes thinner..
Remember the cooking oil? notice how easily it flows once it's hot? (if you're not a cook, ask your wife/live-in girlfriend/concubine!)
Or if you're more involved in cars, take the grease and burn it.. what happens? It melts into oil, right? Grease is oil.. a VERY THICK oil.. how much SAE weight.. I don't know! But probably some huge number... and it's W rating is probably high as well, as it doesn't take a very high temperature to melt.
Same thing with engine oil... A SAE5w30 oil will become thinner than 30 when the engine is running over 100 degrees C, so that's about it..
Thin oil = less protection, so you can see why keeping the oil thick at higher temps is important.
So what's the 5w mean?
The 5w is not the weight.. it has nothing to do with the oil, but rather, it shows how resistant the oil is to become thin at higher temperatures. All oils become thin as they are heated up, and the 5w sort of represents how well the fuel can help keep the oil thick at higher temperatures over 100 degrees C
So a SAE5w30 oil will thin out less than a SAE10w30 oil if you're cooking them in the engine at more than 100 degrees C. So a 5w30 oil is better as the temperature gets hotter.. As to the actual weight at certain heat temperatures.. I don't know.. I never bothered to research!
That's why the SAE0w20 is considered better than SAE5w30, and SAE5w30 is considered better than SAE10w30..
As an example, consider this FABRICATED SCENARIO
If SAE0w20 is heated up to 200 degrees C, the weight of the oil is still SAE20(I'm just putting a random number to illustrate the point, so don't take the number as a definite answer) It should decrease, but I don't know by how much exactly, but it will be less than an oil that has a 5w or 10w rating.
Now SAE5w30 at 200 degrees C, may suffer more, and go down to SAE18 (yet another random number. and at maybe at 300 degrees C, it may be even thinner than SAE0w20 at 300 degrees C. Maybe it will be thin like water, yet the 0w20 will still be like oil, keeping its lubrication properties
And the SAE10w30 at 200 degrees C, even worse, going down to SAE15 or so... and probably will become thin like water even at even earlier temps than 300 degrees C
That's why you find an OLD hot engine starts easier than when cold.. it's because the oil is thinned out enough that there's less resistance for the oil to flow. Since there's probably sludge stuck on the oil passages, the passages are more restrictive, so a thinner oil will flow better!
A possible solution.. NOT!
Why not thicker oils then? if we put in SAE15w100, shouldn't that help protect the engine? Maybe the oil would thin out to SAE30 when heated up?
Thing is, a SAE100 oil would probably look like grease when it's cold, and you can guess how hard is it for the engine to push that grease into narrow oil passages in the engine. Starting up the engine would be a nightmare! That's why some cars can use thicker oils and some cars don't...
Remember that honda engine uses the engine oil to push the dowels to engage the secondary lobe (that's VTEC for you) so that's why honda engine seems to need thinner oils than say, a proton car, and why some people like SAE5w30 in their car rather than the honda recommended SAE10w40, or why people run 0w20 oils on *some* racecars.
A kancil requires even thinner oil because the engine is so small, you can guess how small the oil passages are.
You can probably run thicker oils like SAE15-50, but the engine would probably be harder to start in the mornings.
So that's about it..
The 0w,5w,10w rating is obtained by adding additives to the motor oil.. so more powerful additives are in 0w, a bit less on 5w, and even less on 10w.. That why some mechanics say 0w and 5w is considered synthetic, and 10w is considered semi-synthetic, and a 15w oil is considered non-synthetic..
If you want more info.. you can google up the term "Motor Oil Bible"... it's in PDF format, and the info within is quite accurate when I asked an engineer friend about stuff I learned from it.
I've read it a few years back, so I don't remember exactly what it said.
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