08 Legacy GT - Castrol GTX 10w30 - Viscosity Test

[JoeFromPA]

Hi all,

This is a UOA from a 2008 Legacy GT, driven about 20-24k miles per year. I ran Castrol GTX 10w30 as a bet with a very knowledgable gentleman as to whether or not it would shear down a grade within a normal run for this engine.

Air filtration: OEM (previous runs were an AVO Panel Filter)
Oil Filter: OEM
Driving Style: Relatively normal...some spirited runs and WOT

Analysis: I like it....looks like a very capable dino oil is suitable for this engine's recommended interval without being too weak at the end. Overall wear is boring-good, though the weird Tin noise is a tad concerning.

Oh, also, this oil was in use for about 2 months and this engine consumes no visible oil, ever. It's been a phenomenal car, in that after 45k miles it's required nothing and is a very comfortable cruiser with decent power.

Thoughts?

Joe

 

[JoeFromPA]

P.s. Very happy that the copper dropped. The theory is that the oil coolers on these engines oxidize for awhile. No harm in it, but not something you want to be seeing in your oil reports. Maybe mine has petered out

 

[addyguy]

Looks great - GTX is a very, very stout dino oil.

Castrol has built there reputation, basically, on building shear-resistant oils - it's definetly deserved here!

I'm curious where the extra magnesium comes from - AFAIK, GTX doesn't use it, and the previous oil had less, so.....

 

[hate2work]

What are the other two oils previously used in the report? I'm guessing the M1 and PP listed in your sig.

 

[JoeFromPA]

Spot on, previous runs were:

M1 15w50 and PP 5w30

Prior to Castrol GTX 10w30, this car had seen at least 2 straight runs of Rotella T 5w40 synthetic.

 

[ARCOgraphite]

The Zn (and Mg) are still going into the solute. The wear PPM do not represent the GTX over long use. BTW I would hope a modern 10w30 would be shear stable over <4K OCI - only a 20w40 would be more stable using conventional blending.

 

[JoeFromPA]

Arco - This engine shears most oils. Most synthetics have a hard time holding out 5-6k in this engine. It's one of the reasons the Subaru crowd has been gung-ho on Rotella T 5w40....because it holds up to 7-8k OCIs even in modified 2.5 liter turbos.

Depending on how you look at it, you could say that in another 100-200 miles, this oil would've been down into 20 grade land.

 

[ARCOgraphite]

I dont think "the engine shears oils". I think many folks are using non-stable oil like 5w30 which would shear with anything more vigorous than Grandma driving at 1200 rpm to church. The VII additive that gets trashed firstly , not the oil. If 10w-xx uses 50% less vii then you'll see better results. Why any sane person would use a ILSAC GF4 5w fuel economy oil in a performance engine with high specific output is beyond me. Synthetic? Whats synthetic these days? I bet M1 10w30 HM would hold up 5K.

 

[Patman]

Originally Posted By: JoeFromPA
Arco - This engine shears most oils. Most synthetics have a hard time holding out 5-6k in this engine. It's one of the reasons the Subaru crowd has been gung-ho on Rotella T 5w40....because it holds up to 7-8k OCIs even in modified 2.5 liter turbos.

Depending on how you look at it, you could say that in another 100-200 miles, this oil would've been down into 20 grade land.



How do you figure? At 10.0 cst it's a good distance away from becoming a 20 weight. It needs to get below 9.3 for that to happen. I doubt this oil would shear from 10.0 to 9.3 in just 100 to 200 miles, especially considering the fact that it probably only sheared by 0.5 to 1 cst in the entire run up to that point.

 

[bluesubie]

Test not valid. Run GTX again and go the full 3,750 mile interval.

-Dennis

 

[JoeFromPA]

Patman - Sorry, I was going by blackstone's ranges indicating that 59 SUS and 9.9 CST were the ranges.

BlueSubie - Take it or leave it man I do feel though as if Castrol GTX 5w30 wouldn't have held up as well.

 

[pcfxer]

What was the beginning visc? Without a VOA making assumptions is about as worthless as switching oils based on 10ppm differences (basically what this entire forum is)..

 

[JoeFromPA]

Pcfxer - I agree with your final statement. Took me awhile to learn that

Beginning visc vs. final viscosity is pretty worthless without knowing how much oxidation and other breakdowns occured which could have thickened it....

Oh wait, I'm basically saying almost all my UOAs are worthless. Oh no!

 

[bluesubie]

Originally Posted By: JoeFromPA
I do feel though as if Castrol GTX 5w30 wouldn't have held up as well.

You're probably right.

-Dennis

 

[Jaymus]

I ran GTX 10w30 in my mamaw's 2000 Buick Park Avenue 3.8 V6 for a few years. I tried GTX 5w30 the last oil change. I know how the digital oil psi gauge reacts to different oils, amount of driving, and harshness of the drive.

I've seen that the GTX 5w30 does go down around 3-5psi at idle after 30+ minutes of normal driving compared to the GTX 10w30. But, hey, 33psi at 650-700RPM in drive at a stop is great to me. I do think it thins out more over time than 10w30, though, but I have no proof but this one instance of speculation.