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#1545938 - 07/27/09 01:18 PM Difference between 10w-30 versus 10w-40?
snakyjake Offline


Registered: 07/09/08
Posts: 78
Loc: WA, USA
I understand the 10w, meaning the winter viscosity. But what is the difference between 30 and 40?

The 10w makes sense...lower rating means oil flows thinner at low temperatures. Therefore better lubrication at startup when it's freezing.

30 vs. 40?
40 weight is thicker (not sure how much more), but not sure what the advantages are. Less oil consumption with the 40? Better for old and loose engines? Does the 40 provide better protection and more cushion/compression against metal?

What advantages/disadvantages are with 30 weight?

Is there a problem stretching the oil viscosity chains from 10-30 to 10-40 (differences of 20 vs. 30 spread)?

Thanks,

Jake

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#1545953 - 07/27/09 01:35 PM Re: Difference between 10w-30 versus 10w-40? [Re: snakyjake]
addyguy Offline


Registered: 09/08/05
Posts: 13429
Loc: Canada
'Upper' oil weight are 'ranges' of viscosities at 100 degrees C, measured if centistrokes (cst).

A 30-weight oil is between 9.3 and 12.4 cst at 100C. A 40-weight oil is between 12.4 and 16.8 cst at 100C.

So, you can have 'thin' and 'thick' oil within the same oil grade - ie, Havoline 5W-30 is 9.7 cst@100C; while Maxlife 5W-30 is 11.5 cst@100C.

Viscosity Index Improvers (VII's) are what make muti-viscosity oils thicker. Generally, most on here see them as bad things - they don't lubricate well, and they 'break down' and can get cooked into sludge - but this was much more true 25-30 years ago than today.

There is a huge, huge debate here about whether thicker oils actually protect better, or whether thinner ones do - you'll have to read all those threads for yourself.

Often, if an engine has a lot of wear, a thicker oil will reduce oil consumption by reducing the amount of oil that can 'escape' through larger openeings, but not always.
_________________________
2003 Mazda Tribute LX V-6, 172k miles.
Oil: QS Defy 5W-20; Fram Ultra XG2 filter.

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#1545963 - 07/27/09 01:46 PM Re: Difference between 10w-30 versus 10w-40? [Re: addyguy]
hate2work Offline


Registered: 09/04/08
Posts: 4617
Loc: Western Washington

Jake, are you still running the AME from Amsoil? That's a great oil, for sure.
_________________________

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#1546176 - 07/27/09 06:13 PM Re: Difference between 10w-30 versus 10w-40? [Re: snakyjake]
d00df00d Online   content


Registered: 10/20/05
Posts: 9218
Loc: PA
 Originally Posted By: snakyjake
30 vs. 40?
40 weight is thicker (not sure how much more), but not sure what the advantages are. Less oil consumption with the 40? Better for old and loose engines? Does the 40 provide better protection and more cushion/compression against metal?

Sometimes, yes, and yes. Disadvantages are increased drag, higher temps, and slower circulation in tight spaces; these may or may not be significant depending on the engine and conditions.


 Originally Posted By: snakyjake
Is there a problem stretching the oil viscosity chains from 10-30 to 10-40 (differences of 20 vs. 30 spread)?

Depends. Synthetic or dino?

All else equal, a bigger spread means higher volatility and a greater need for VIIs (as addyguy mentioned). This might be an issue with a dino oil, but not so much with a synthetic.
_________________________
2011 Mazda RX-8 R3
Castrol GTX 5w-20

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#1824201 - 03/20/10 09:02 AM Re: Difference between 10w-30 versus 10w-40? [Re: d00df00d]
jorton Online   content


Registered: 07/04/03
Posts: 2756
Loc: San Antonio, TX
The upper number 30, 40 represents viscosity at normal summertime operating oil temperature. Viscosity is resistance to flow. Hot oil is thin so it needs to have some resistance to flow in order to prevent metal to metal contact. 20 and 30 weight oil has correct viscosity for new domestic gasoline powered passenger cars and trucks.

Switching to 10w-40 is common RX for older cars that have or may have low oil pressure.
_________________________
"If everything seems under control, you're just not going fast enough."
- Mario Andretti



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#1824790 - 03/20/10 05:39 PM Re: Difference between 10w-30 versus 10w-40? [Re: jorton]
ps49556n Offline


Registered: 01/07/10
Posts: 124
Loc: NYC
Follow your mfgs guidelines, otherwise use a series of UOAs to determine the best viscosity.

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#1824830 - 03/20/10 06:09 PM Re: Difference between 10w-30 versus 10w-40? [Re: ps49556n]
beast3300 Offline


Registered: 12/24/09
Posts: 3012
Loc: Ohio
Viscosity doesn't equate to protection. For the most part 10w40 is obsolete. We service cars/trucks from small to big and use the recommended viscosity. All the Ford trucks with gas motors get 5w20 regular oil, even F350s.

I personally have used 5w30 in my supercharged Regal since fall of '08 to now. In my opinion 10w30 is obsolete in most situations, both in cars built from the 80s to now.
_________________________
'03 Regal GS L67: PUP 5w30/XG3980, Filtermag

'99 Grand Prix L36: QS Dexos blend 5w30/PF47 Classic, Filtermag


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#1824839 - 03/20/10 06:20 PM Re: Difference between 10w-30 versus 10w-40? [Re: beast3300]
Catera Offline


Registered: 12/23/09
Posts: 197
Loc: Michigan, USA
The thing is if you have an 80s or 90s ride, you cant just jump to the 5W-20 oil, you will find yourself in a lot of trouble...

If you got an older car and its running fine stick to 5W-30 winter and 10W-30 summer, if it burns some oil try the 10W-40 and see if it helps.

If you got a new ride, lets say 2005-up and it says to use 20weight oil then do that, dont go 30-40...

Engines of each era are calibrated and designed in a specific way and its best to stick to those regulations...

My car suggest 10W-30 or if very hot a 10W-40 oil but in winter if temps are way too cold it calls for 5W30 or even 0W-30... for say up at the north pole...
_________________________
2K1 Cadillac Catera Sport
L81 54 V6 24V 195RWHP 142.5K
Latest oil change.
5qt Mobil 1 HM Non-EC(10W-30)
3/4qt HDMO Rotella T (15W-40)
8oz. MMO

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