Viscosity, wear, engine failure, oh my!

[drninja]

I've searched but haven't found a discussion on this topic. I'm trying to wrap my head around kinematic viscosity and how it relates to engine wear/failure.

I drive an 04 WRX and as you probably know, the WRX community at large freaks out about the manufacturer recommended 5w30 oil. Many claim it is too thin, shears down to a 20-grade, and causes spun bearings and other horrors. They often recommend 5w40 and 15w40 HDEOs as an alternative.

However, if you read the "Motor Oil University" articles on the front page of BITOG, there is a large section on viscosity that brings up an interesting point: If most wear occurs on startup when the engine is cold, why is it better to move up a grade to an oil which has a significantly higher viscosity at 40C and a relatively minor difference in viscosity at 100C? In fact, the author of the article states he often moves down a grade from manufacturer's recs.

Using Pennzoil Platinum 5w30 and Shell Rotella T6 5w40 as comparisons:

Pennzoil Platinum
40C cSt - 57.5
100C cSt - 10.3

Shell RT6
40C cSt - 87
100C cSt - 14.2

Difference at 40C: 29.5 cSt
Difference at 100C: 3.9 cSt

If you use 15w40 Rotella T (as many say is fine in this car), the difference at 40C is 42.5 cSt.

Why is this a good trade-off to make? Can a 3.9 difference in cSt really be the difference between the engine being properly lubricated or not? How does the application change if the car is making frequent short trips, with occasional weekend trips? Anyone mind helping a noob understand this stuff?

Thanks!

 

[Rand]

Turbocharged hard driven engines are different than most engines.

You could always use a 0w40 if cold start wear bothers you.

also 40C is hardly cold start temps.

If you have an oil pressure gauge and oil temp gauge (real ones not fake gauges) Then you can use whatever you want within reason.

 

[chubbs1]

I really have seen a lot of great used oil analysis with 5w40 in that engine. Now some people say you can't totally base wear on a simple UOA but I think it has shown fairly consistently that the 5w40 is a great oil for that engine.

I would say to split the difference a little bit and pick up some Mobil 1 0w40, it has good startup characteristics and usualy shears to a solid (upper) 30grade. You get the best of both worls and the Mobil 1 is usually on sale. AZ and AAP will be having it next month I bet. I think AZ already has it. AAP is usually a better deal.

 

[drninja]

Thanks for the recommendations so far. I'd love to start a discussion about the science behind these recommendations, so if anyone has any in-depth info, I'd love to hear (read?) it.

 

[d00df00d]

to BITOG!

I've read several threads about the supposed issues with 5w30 oils in Subarus. I haven't seen a single one in which oil starvation or some other issue could be ruled out as a cause of whatever failure the poster was complaining about. In other words, no legitimate reason whatsoever was ever given to blame the oil rather than the owner. If you've seen otherwise and can provide a link, I'd love to read it.

As for viscosity, remember two things:

1. There is a LOT more to oil than its kinematic viscosity. The oil's other properties need to be appropriate to your application.
2. You always want your oil to be as thin as possible, and as thick as necessary. Oil viscosity increases drag, and thus heat as well. That's why you want the oil to be as thin as possible while retaining enough viscosity to protect your engine.

Frequent short trips may change the calculus in favor of thicker oils IF your engine fuel dilutes (i.e. fuel gets into the oil) under those conditions. However, if your oil change intervals are relatively short, it may not be an issue. Oil analysis is the easiest way to get some idea of what you're dealing with on this point.

Hope that helps.

 

[Skid]

Startup, as auto engineers define it, takes about 20 minutes. It's the time it takes for your engine to hit equilibrium temperature, meaning, the last part on your engine stops getting any warmer.

Startup wear itself has almost nothing to do with viscosity or flow at normal temps. It has to do with condensation of water from blowby onto internal surfaces coupled with the CO2 from blowby. The result is acid etching, which should be neutralized by the KOH in the oil, if your oil is fresh enough. That being said, running something like 20W-50 or straight 40 in Canada in the Winter would be pretty stupid.

Residual oil protects your engine upon the "startup" that most people think of as startup.

For cars like the WRX that are driven hard, HTHS is the parameter to look for. I'd run something thick if I had one of those, but an 04 car is getting pretty old to drive hard.

Good luck.

 

[JAG]

HTHS viscosity is what best correlates to minimum oil film thickness in bearings when the oil is up to normal temperature. There is a significant percent increase in HTHS viscosity between Pennzoil Platinum 5w30 and Rotella T6. Yes most wear occurs at startup but it's not soley due to viscosity. There is a lot of bad chemistry going on then too. Antiwear additives are not functioning ideally, more water condensate is corroding surfaces and messing with the oil. There are some good past threads on this.

 

[d00df00d]

Originally Posted By: chubbs1
I really have seen a lot of great used oil analysis with 5w40 in that engine. Now some people say you can't totally base wear on a simple UOA but I think it has shown fairly consistently that the 5w40 is a great oil for that engine.

For all practical purposes, you can't assess wear at all based on a simple UOA.

With the cheap one-off used oil analysis that almost everyone does, it's possible for a failing engine to produce great-looking results, and for a perfectly fine engine to produce poor-looking results. You need to step up to the more expensive test packages to start to get actionable information, and even then it's fairly sketchy.

Cheap used oil analysis can be just fine for tweaking oil change intervals, though.


Originally Posted By: chubbs1
I would say to split the difference a little bit and pick up some Mobil 1 0w40, it has good startup characteristics and usualy shears to a solid (upper) 30grade. You get the best of both worls and the Mobil 1 is usually on sale. AZ and AAP will be having it next month I bet. I think AZ already has it. AAP is usually a better deal.

To add to this, it's one of Mobil's flagship products and until very recently didn't even have a rival among its competitors in terms of high-performance third-party approvals.

To be clear, I'm not endorsing switching to a thicker oil just because of some panic on Subaru forums. However, in the world of off-the-shelf xw-40s, Mobil 1 0w-40 probably is just about as good as it gets.

 

[d00df00d]

Originally Posted By: Skid
an 04 car is getting pretty old to drive hard.

Don't tell my '96 car that.

 

[drninja]

Originally Posted By: d00df00d

to BITOG!

I've read several threads about the supposed issues with 5w30 oils in Subarus. I haven't seen a single one in which oil starvation or some other issue could be ruled out as a cause of whatever failure the poster was complaining about. In other words, no legitimate reason whatsoever was ever given to blame the oil rather than the owner. If you've seen otherwise and can provide a link, I'd love to read it.


I've never seen otherwise either. That's why I made this thread. I'm trying to separate fact from group-think fiction. Thanks for the response!

 

[drninja]

Originally Posted By: Skid
an 04 car is getting pretty old to drive hard.


It's stock and I don't drive hard. Never sees redline. Maybe 5-6k on an on-ramp every once in a blue moon.

 

[OVERKILL]

Originally Posted By: Skid
but an 04 car is getting pretty old to drive hard.


Huh?

I beat on my '87 5.0L like a red-headed step-child. The engine out-lasted the car and is awaiting home #3.

I also drive the M5 as it was meant to be driven.....

There is nothing inherent in a vehicle's design that stipulates age as a decider as to whether it should be driven hard or not.

 

[Skid]

Originally Posted By: OVERK1LL
Originally Posted By: Skid
but an 04 car is getting pretty old to drive hard.


Huh?

I beat on my '87 5.0L like a red-headed step-child. The engine out-lasted the car and is awaiting home #3.

I also drive the M5 as it was meant to be driven.....

There is nothing inherent in a vehicle's design that stipulates age as a decider as to whether it should be driven hard or not.


I'm happy for ya.

 

[OVERKILL]

Originally Posted By: Skid
Originally Posted By: OVERK1LL
Originally Posted By: Skid
but an 04 car is getting pretty old to drive hard.


Huh?

I beat on my '87 5.0L like a red-headed step-child. The engine out-lasted the car and is awaiting home #3.

I also drive the M5 as it was meant to be driven.....

There is nothing inherent in a vehicle's design that stipulates age as a decider as to whether it should be driven hard or not.


I'm happy for ya.


I am sure you are.

However, I'm simply qualifying my experience, and that of many others who don't use age as some sort of vehicle treatment metric.

You made the initial statement, so what is the logic behind it?

 

[drninja]

Wow. Derailed already?

 

[OVERKILL]

Originally Posted By: drninja
Wow. Derailed already?


That happens a lot here, LOL.

Regardless, some good advice was given to you on the first page and things were pretty well explained.

A good compromise may be an oil like Mobil 1 0w40. It is a light 40-weight, and is approved for a huge list of high performance apps, including many that are turbocharged. It also has a reasonable high HTHS.

 

[drninja]

What about the HM products from Mobil 1? I know the 5w30 is ACEA A1/B1. Isn't that an indicator of the HTHS level? It's a bit more readily available in my area than the 0w40

 

[OVERKILL]

Originally Posted By: drninja
What about the HM products from Mobil 1? A little more readily available in my area than the 0w40


IMHO, the 0w40 is a better oil. Is it not available at your local Walmart?

 

[semaj281]

Originally Posted By: drninja
What about the HM products from Mobil 1? I know the 5w30 is ACEA A1/B1. Isn't that an indicator of the HTHS level? It's a bit more readily available in my area than the 0w40

ACEA ratings are meant for diesel engines. And it's hard to know the HTHS levels without looking up the MDS for the oil.

If 0w40 is hard to find, what about Mobil 1 Turbo Diesel Truck 5w40? And Redline?

 

[d00df00d]

Originally Posted By: semaj281
ACEA ratings are meant for diesel engines.

ACEA Ax is for gas engines.
ACEA Bx is for diesel engines.
ACEA Cx is for sensitive emissions systems.

http://www.acea.be/images/uploads/pub/070308_ACEA_sequences_2007_LD_and_HD.pdf


Originally Posted By: semaj281
And it's hard to know the HTHS levels without looking up the MDS for the oil.

True, and some MSDSs don't even list it. However, there is at least some information you can glean. For example:

ACEA A1 requires an HTHS viscosity of 2.6 to 3.5 for xw-20 oils, or 2.9 to 3.5 for all other grades.
ACEA A5 requires an HTHS viscosity of 2.9 to 3.5.
ACEA A3 requires an HTHS viscosity of 3.5 or more.