LOW weight (5w-30) vs. HIGH weight (15w-40+) oils...

Me so confused!

I thought that oils got thinner as they got hotter. Therefore, a 5W-30 oil would be 5 weight when hot and 30 weight when cold. How can 5W-30 and 10W-30 be the same viscosity when hot?

>"When the engine is hot a 0W-30, 5W-30, 10W-30 or straight 30W oil have the same viscosity."

Please, the dummy over here needs a "lighter weight" oil lesson!

Birdman

 

Oils do get thinner as they get hotter.
5W30 means that the oil acts like a 5 weight oil when cold and acts like a 30 weight when hot. where 'W' means 'winter' not 'weight'.
Modern synthetic oils are so good at not thinning out when hot that lighter weight oils protect just as good as older thicker oils, have lower pumping losses,...

 

Mitch,
I'm still confused. They get thinner when hot....how can 5W-30 be 30 weight when hot and 5 weight when cold? The larger number means it's thicker, right? A 30 weight oil for example is thicker than a 10 weight oil and thinner than an 80 weight oil. (Gear oil is pretty thick and runs in the 80 weight range).

I'm clearly missing something here.

Birdman

 

Oils is not easy. Typically nobody understands it although most think they do. It is not common sense and the nomenclature just makes it worse. I have heard many explanations and they all confuse people. I do not know how to put it.

My latest explanation is that the lower the first number the less the oil resembles honey when your engine starts up. The second number is the thickness of the oil at regular engine operating temperature. The two numbers are independent and not related. This explanation is not a biochemical one but a way to understand the relationship.

Motor oil, as it is, can never be too thin when cold. It will always be too thick. That is why the first number must always be a low as possible. Soon there will be -5W-30 (minus 5 or negative 5) and -10W-30 wt oils. They will still be honey like at start up but less honey like than 0W or 5W-30 oils. They will all still have the same viscosity at operating temperatures, 30.

aehaas

 

From SAE J300 p.2

"Two series of viscosity grades are defined in Table (1): (a) those containing the letter W and (b) those without. Single viscosity grade oils with the letter W are defined by maximum low temperature cranking and pumping viscosities and a minimum kinematic vis. at 100C. Single grade oils without the letter W are based on a set of minimum and maximum kenematic viscosities at 100C and a minimum high shear rate vis. at 150C. The shear rate will depend on the test method. Multi viscosity grade oils are defined by both of these criteria....

The W is just a designation of one type of testing vs another.

See how complicated these things are.

aehaas

Addendum: 100 weight gear oil has the same viscosity as 30 wt engine oil. These are the facts. Why they did it this way I do not know.

 

Now how much of an engine's power is used to move the vehicle versus how much is used to overcome internal friction, particularly with a low rpm engine. SUV's generally weigh over 5K lbs. An oil change to a lower viscosity will only get you a very, very few horsepower. It takes a lot of horsepower to move the vehicle. Now how does that very few horsepower translate into 30% more mileage?

Believe him if you choose. Numbers don't back up what he is saying. Internal friction is a minor loss when it comes to what it takes to make large, heavy vehcles move.

 

I put new air filters on my Expedition. At the same time (about 45,000 miles) I changed the transmission fluid for the second time. I used the stock Ford stuff recommended in the owners manual. I went from a 5W-30 Pennzoil to a 5W-20. I also changed the differential gear lube from the 70W-140 that was in there to Mobil 1 75W-90. I do not use the car for towing or any heavy loads for that matter.

I drive a consistent route to and from work. I was getting 14.5 MPG and then got 15.5 MPG afterwards.

People for some reason argue the point. These are the facts. I am not making any claims or guesses. I am just stating what I did.

aehaas.

Smart people learn from their mistakes. Really smart people learn from other people's mistakes.

Lawrence,
My guess is that the internal friction of his engine is 30 HP and it takes 10 HP to push the car down a level road at 40 MPH. If the internal friction can be reduced to 20 HP that would be a big gain.
Also, he takes short trips so the engine never gets hot. His old oil was as thick as glue, the new oils is much thinner when not up to operating temperature. It seems plausible to me.
Indy cars use thinner oils for getting higher speeds during polling. Then they go to slightly thicker oils for the long race. There must be something to it.

 

I've heard that some drag racing teams use only a little lightweight oil or no oil at all to get the highest performance -- and they also tear down the engine after each run.

It appears that lower weight oils do offer measurably higher performance, better efficiency, etc. Nevertheless, this MAY NOT have anything to do with what most of us are looking for -- namely: longer trouble-free engine life.

Kind Regards, Chris

 

High compression dragsters typically use thick oils like 50 or 70 or 90 wt. The reason is because of the blow-by gas that dilutes the crankcase oil. At the end of the drag the oil is as thin as water.

aehaas

 

the recent influx of ultra low weight oil (i.e., 0-20, etc.) is sedimented upon new trends in environmental politics and machining; namely, lower weigh oils, and the promotion of longer oil change intervals appease the eco mongers. conversly, what makes the use of these oils possible is two fold on the engineering front: 1. , more advanced and robuts additivies &proprietary anti-friction cocktails; 2., amazingly clean machining surfaces, and nearly air tight engine clearances (have any of you mic'd or spec'd a modern japanese engine? the machining is impecible).

f1 teams, may or may not, use very light weight oil. however, shell has an entire lab dedicated to the development of more advanced mixes, and proprietary anti-friction cocktails being developed around the clock. ( i personally doubt the weight of the oil used would be divuldged to a public person as this is privelaged information). however, lets also not forget that tremendous oil capactities that f1 cars run (i.e., mclarens aux oil tank) and the efforts taken to keep the oil cool, fresh and circulating -- street cars, even dry-sumped, are pretty rudimentary in compraison.

when people switch from dino juice to syn. , and they have worn/high milage seals they'll notice some weeping b/c on avg syn oils are thinner; since their weights are engineered, they're not guesstimates. this is unlike dino juice where the weight is an avg, or guess.

at the track, you want to run as heavy as a weight to take the added prolonged heat, but you don't want to run too heavy a weight where it'll create a power/lubrication efficency deficency on account of the added parasitic lose due to the extra worl the oil pump, oil pump gear etc are forced to exert.

sorry i can't expand further, but i'm really pressed for time here @ the lab today.
hubert -

 

I will add to what Hubert said here about dino oils being different. This is my theory alone and it is very rough, not very detailed.

The point is that synthetic oils are thinner. Let us look at a 30 wt. dino and a 30 wt. synthetic. Both fall within the SAE specs at 104F and 212F. The syn. is based on a single medium length oil molecule. The dino has short, medium and long molecules but the majority are medium length. They are not pure and are very mixed but the average viscosity falls in the tested range.

At very low temperatures like around 40F and lower the syn. is much thinner than the dino because those very long molecules keep the dino stuff from thinning. It cannot be pumped easily. The syn. pumps very well, it is simply thinner, moves better and lubricates more effectively. This is documented in testing as all syn oils have lower pumping and pour points than the same wt. dino oils.

At very high bearing temperatures the dino is actually thicker than the syn. This is because it has those extra long molecules in there. This creates drag and reduces oil flow and lubrication. The syn is thinner, gives better flow and therefore better lubrication and a longer engine life. Also, over time, dino oils first thin then thicken considerably. A 30 becomes a 20, then back to 30 then 40 and 50 wt. Synthetic oils stay the same viscosity throughout their life in your engine. These last two statements are facts.

I conclude that synthetic oils are in fact thinner when cool and thinner when hot therefore giving better lubrication from better flow at the extremes of temperatures. Again, this is a comparison of oils of the same wt. class, a 30 wt oil.

aehaas

PS I have been able to get information out of oil companies. It is worse than pulling teeth. Shell is the worst one. Yet I have on occasion been able to pry a little out of them. For example I once posted the specs of Shell transaxle oil that is proprietary for Ferrari.

PPS I just had a call back from Cathy at API. She confirmed that the W in 5W-30 does not stand for "winter" and does refer to wt. and testing methods as I outlined earlier.

 

Aehass, I'm just a dumb accountant so I'm only following half of this, but I can't remember which half...

I brought this up to the techs at FOH, and they want to stick with the factory recommendations. Because I just purchased a warranty on my 98 Maranello, I've have to go with this for now.

But, what do you recommend at start up to minimize damage, regarding of which oil is being used?

I typically start the car and let it idle for a minute or two before backing out. Then initially I drive like the old man that I am. I run no higher than 2,500 to 3,000 in 1st before shifting to third, where again I don't go any higher than 3,000. I also don't turn on the A/C until the car is rolling freely.

I don't apply much power until I feel the car warm up. Sorry I don't have any better way of explaining this. The car just feels more limber as it gets hotter.

What am I doing right, and what am I doing wrong?

Thx, Dale

 

I'm just a dumb kid that plays with molecules all day, but this is what i know.

the primary function of motor oil is to provide a molecular barrier between moving components in the engine; namely, the pistons and piston walls. this is why when you blow an piston ring, you score that cylinder b/c the oil getting pumped in there is burned up, and the "protective film" is eaten by the combustion process... mind the huge plum of smoke trailing your car.
first, motor oil blends, work to give immediate lubrication on start - up. hence they're 10 weight because you want the minimum amount of viscocity on start up to allow the oil pump to prime the engine quickly when cold. 30 weight when hot (for example) means the viscocity of the oil increases with rising operational temp. the reasoning behind this is actually quite simple: with increased friction, you have increased heat, and vice versa; therefore, you'll want a thicker oil (i.e., a more robust molecular barrier) present to cope with the increased thermal strees of it's operational environment. these stressors are also why you have things like zinc, etc in modern oil medlies as they provide a greater degree of protect -- considering the fact that they're "hard" ions. this is also the reason why synthetic oil provides a greater degree of protection, and why petroleum co.'s spend millions coming up with proprietary blends of anti-friction cocktails. we can also get into the new 0 weight oils, and the implicit reduction of sheering, and lubrication system parasitic losses and oil pump pressure reduction, but that's an aside. you can also invest less power on oil pumps, etc.
in closing, you should do two things: 1. use a weight of oil that's sufficently thin at start up to allow your lubrication system to apply that coat of protection to all of the reciprocating parts of your engine in a facile manner, and 2. allow your engine oil pressure to build to the appropriate pressure as you want you system to be able to provide you with ample lubriaction under full load.
a comment on oil pressure -- you usually get =/> 75% of full oil pressure within seconds of start up. this is to allow for immediate lubrication of critical components (crank, rods, pistons, etc), the remainder of the oil pressure is built up within minutes after the initial start -up, but this is usually directly proportional to water temp (if your car isn't equipped with a oil pressure gauge). so, if you need to "eyeball" it, just wait until your water temp is up in the right range, and then feel free to step on the loud pedal -- this is to usually used anyway as an anecdotal empirical footnote anyway.
in closing, if you're deciding b/w a 5-40 and a 10-40, and you're concerned, then use the 5w, but you will notice some increased oil consumption. however, this is also dependant upon ambient temps. in TX, doc, you're ambient temps don't fall all that far, so you'll get eq. protection with a 5 and a 10. i use 10, b/c i track my car, and it burns less with the 10 - 30 v. a 5-30.
aww hell, i left the bunsen burner on... gotta go...

 

If you want to use what the warrantee calls for I am sure it will work. For sure, all oils that use the lowest first number the better. 0W-X is better than 5W-X is better than 10W-X for all applications, period.

Ok on not taxing the engine until warm but the best is to get in and go, not warm it up at idle. Start, go easy until warm then let 'er rip.

aehaas

 

Many 'old line' mechanics seem terrified of synthetics and leaks in old cars. If your seals are in any kind of reasonable shape, you won't have any problems. My 29 year old car is using Mobil 1, and is dry - except for a stubborn front distr, which has leaked since new. The PO used Castrol 'dino' oil and it leaked. It still leaks with Mobil 1, but I'm working on it! At the moment, it's dry, but we'll see.

 

Thanks AEHass, I think I get it now. I thought the "5" in 5W-30 was a viscosity number. Being lower than the "30" I was assuming that the oil was 30 weight when cold and 5 weight when hot, which would make sense since they get thinner as they get hotter. Man, I have been clueless for a while!

So the first number is some kind of a "cold factor" that describes how much thicker the oil gets when cold. I would love to know what the number actually means and how it's derived. I hate numbers that I don't know what they actually stand for!

Birdman

 

Let me make an example. The numbers are not exact but demonstrate the principal:

Straight 5W oil has a viscosity at start up - 40
Straight 5W oil has a viscosity at operation - 4

Straight 30W oil has a viscosity at start up - 100
Straight 30W oil has a viscosity at operation - 10

Note each oil thins as it heats up. Now for the multi vis:

5W-30 oil has a viscosity at start up - 40
5W-30 oil has a viscosity at operation - 10

Most engines need a viscosity of 10 for normal operation. If oils could have a viscosity of 10 with a cold engine and 10 in a hot engine then we could just get in the car and step on the gas. It would not have to warm up.

The best we could do is use a multi-viscosity oil that acts as a 5W when cold and 30W when hot.

aehaas

 

Try http://www.repairfaq.org/filipg/AUTO/F_oil_facts.html. Keep in mind that this document is fairly old (1996), so don't put too much stock in the analysis sections for oils as they were formulated back then. (Oils tend to change formulas frequenly.)

 

My BB512i manual calls for Agip SINT2000/10w50 oil. But, the new Agip SINT2000 oil is 15w50. I have used the 15w50 oil with no problem thus far.

 

Aha! Now I get it!! Oil viscosity is always defined at it's thickness at 212 F. So, when they say an oil is "5W-30"...

When hot, the oil has the viscosity of standard 30 weight oil.

When cold, the oil has the viscosity of what standard 5 weight oil WOULD have at 212 F (which is about 40 weight, a bit thicker than 30, but not as thick as the 30 weight oil would be when cold.)

NOW I finally get it!

Birdman

 

interesting comments.

one observation is, we assume that we need lower visc oils for cold start and many comments to suggest that say a 0-40 or 5-40 is what we should be using in modern engines.

So why is it then that Ferrari stipulate shell helix 10/60 for the enzo when if we follow this thread the conclusion would be that it should be 0/40?

 

Repeat:
Straight 5W oil has a viscosity at start up - 40
Straight 5W oil has a viscosity at operation - 4

Straight 30W oil has a viscosity at start up - 100
Straight 30W oil has a viscosity at operation - 10

Note each oil thins as it heats up. Now for the multi vis:


5W-30 oil has a viscosity at start up - 40
5W-30 oil has a viscosity at operation - 10


Most engines need a viscosity of 10 for normal operation. If oils could have a viscosity of 10 with a cold engine and 10 in a hot engine then we could just get in the car and step on the gas. It would not have to warm up.

The best we could do is use a multi-viscosity oil that acts as a 5W when cold and 30W when hot.


Engines run at operating temperature. If the engine is to run on the track it will be as hot as they get. If the engine calls for 60 wt oil on the track then that is what is needed. But again, a 0W-60 is better than a 10W-60 is better than a 20W-60 (if there was such oils) becasue the 0W-60 would be less honey - like at start up. And at the track they would all be 60 wt.

aehaas

 

ok, probably a stupid question but;
So does the oil pump start pumping oil when the key is at the "on" position or only when the vehicle is actually started? Or is the oil pump "Primed" ready to push oil when the vehicle is started?

 

Oh and this site says the "W" is for winter.
"The W means the oil meets specifications for viscosity at 0 F and is therefore suitable for Winter use."
good info on there.

 

In light of the posts on this subject I rang technical at Castrol in order to obtain a castrol rather than a shell product.

The advice I got from them is that I should NOT use a 0/40 and the recommended product from them was RS 10/60 for normal use.

I then asked for some comparisons between helix ultra and castrol rs and at 100dg the helix oil is 7% thicker. So although oils have to stick to a suggested standard it would seem there are differences albeit small ones

Its left me all very confused, probably better stick with 5/40 shell which is what Ferrari suggest I just dont want to take the chance.

One thing Castrol mentioned was as the (0) oil is very thin when cold one can get more oil 'draindown' so for a moment in time although a thinner oil flows quicker to the parts, its just as well as the oil has dissapeared into the sump.

Im not an oil expert by any means bt this does sound plausable??