5w-30 cst

[Gokhan]

Originally Posted By: semaj281
On that note, I found a handful of UOAs with Group III 5w-30 that still showed 10.3-10.8 cst after 6000 miles.

Of course, new-oil starting viscosity is also key in determining the used-oil viscosity, as there is a large range allowed by SAE. In addition, after the initial viscosity-index-improver-degradation-induced shear (happens after about first 1000 miles or less), the viscosity usually starts to slowly but uniformly increase again due to oxidation, sludge, etc.

You can usually tell if your viscosity is sufficient. If there is no excessive oil consumption, smoke, power loss, or fast oil degradation, your engine is probably doing OK and chances are that you don't need higher viscosities. A UOA can also be of added assurance.

 

[CATERHAM]

Originally Posted By: Gokhan
Originally Posted By: semaj281

You can usually tell if your viscosity is sufficient. If there is no excessive oil consumption, smoke, power loss, or fast oil degradation, your engine is probably doing OK and chances are that you don't need higher viscosities. A UOA can also be of added assurance.

Or save you money on usually worthless UOAs and invest one time in an oil pressure gauge and learn first hand exactly what your engine's operational viscosity is every second it is running.

 

[OldCowboy]

Originally Posted By: Merkava_4
You'll get much better lubrication out of a 30wt.


Old wives tale without a shred of truth. As CATERHAM has noted, the only way to really know what viscosity your engine needs is with an oil gauge. 30 wt is too heavy for most low output engines.

 

[semaj281]

Originally Posted By: OldCowboy
30 wt is too heavy for most low output engines.

That depends on the engine. Both of the Nissans in the "family fleet" call for 5w-30. And they produce less power than my Mustang which calls for 5w-20.

 

[TFB1]

Originally Posted By: OldCowboy
30 wt is too heavy for most low output engines.


Bah, the span between most 20W & 30W is around 2 cSt, not much chance the engine or owner would know the difference...

 

[Gokhan]

Originally Posted By: CATERHAM
invest one time in an oil pressure gauge and learn first hand exactly what your engine's operational viscosity is every second it is running.

I am not sure how useful it would be to monitor oil pressure with a healthy engine. Since car internal-combustion engines don't use hydrostatic lubrication (lubricating parts separated by oil pressure), higher oil pressure doesn't help. In fact, it hurts by straining the engine parts. I think oil-pressure- and oil-flow-wise you will always be better off with lower viscosities but let me know if there is something I am overlooking.

You will always get more oil flow, which means more cooling and lubrication, with lower viscosities. Using lower viscosity will result in lower oil pressure but still more oil flow.

Of course, this doesn't mean that you can use xW-20 with any engine, as some engines require xW-30 or xW-40 to maintain oil-film thickness at bearings and cylinders. This may be especially true for pre-1980s engines, which run dirty and thinner oil film may not be sufficiently thick to prevent large abrasive dirt particles from grinding between sliding metal surfaces.

But then chances are that an ILSAC GF-5 xW-20 will give the best wear, cleaning, and fuel economy results with most modern gasoline engines, unless the engine has problems. As I said in my previous post, if there is no tailpipe smoke, leak, excessive oil consumption, power loss, or fast oil deterioration, your viscosity is probably sufficient and you're probably doing good oilwise.

 

[LordAbbett]

"
Originally Posted By: Gokhan

invest one time in an oil pressure gauge and learn first hand exactly what your engine's operational viscosity is every second it is running.

I am not sure how useful it would be to monitor oil pressure with a healthy engine. Since car internal-combustion engines don't use hydrostatic lubrication (lubricating parts separated by oil pressure), higher oil pressure doesn't help. In fact, it hurts by straining the engine parts. I think oil-pressure- and oil-flow-wise you will always be better off with lower viscosities but let me know if there is something I am overlooking."

"You will always get more oil flow, which means more cooling and lubrication, with lower viscosities. Using lower viscosity will result in lower oil pressure but still more oil flow."

Are you talking about a cold start or high RPM where you might be in pump relief? There I can see more flow from the thinner oil. But hot oil and oil pressure below pump relief; why would it pump more 5w20 than 5w30. Sure the pressure would be higher but wouldn't it have to bypass oil to decrease flow?

A real oil pressure gauge would tell you if this was happening

 

[OldCowboy]

Originally Posted By: TFB1
Originally Posted By: OldCowboy
30 wt is too heavy for most low output engines.


Bah, the span between most 20W & 30W is around 2 cSt, not much chance the engine or owner would know the difference...


By too heavy, I mean heavier than necessary. Considering Pennzoil Platinum, 5W20 has a viscosity of 8.48 and 10W30 10.5. That is essentially a difference of 2 cSt, meaning the 20 wt is 23% lighter at 100C. It is 35% lighter at 40C (46.84 vs 63.4).

I am aware of no data that shows that engines which are spec'd for 20 wt oil show lesser wear with 30 wt oil.

 

[Gokhan]

Originally Posted By: LordAbbett
Are you talking about a cold start or high RPM where you might be in pump relief? There I can see more flow from the thinner oil. But hot oil and oil pressure below pump relief; why would it pump more 5w20 than 5w30. Sure the pressure would be higher but wouldn't it have to bypass oil to decrease flow?

A real oil pressure gauge would tell you if this was happening

I should have perhaps said a thinner oil will always give you the same or more flow -- and with same or less oil pressure -- than a thicker oil. This statement covers all temperatures and RPMs.

 

[FastGame]

Originally Posted By: OldCowboy
By too heavy, I mean heavier than necessary. Considering Pennzoil Platinum, 5W20 has a viscosity of 8.48 and 10W30 10.5. That is essentially a difference of 2 cSt, meaning the 20 wt is 23% lighter at 100C. It is 35% lighter at 40C (46.84 vs 63.4).

I am aware of no data that shows that engines which are spec'd for 20 wt oil show lesser wear with 30 wt oil.


Do you know of any data the shows more wear on engines spec'd for 20 wt oil ?

 

[OldCowboy]

Originally Posted By: FastGame

Do you know of any data the shows more wear on engines spec'd for 20 wt oil ?


I do not.

 

[FastGame]

Thanks