Oil viscosity and the owners' manual

[Rattnalle]

That is my concern, too with switching to the 15w-40, dm635. We don't get cold that often, but we do have several days a year when we're into the teens and twenties, and those are the days I'd like to take the 960 out.

I really do appreciate everyone's feedback on it.

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Simplify a bit and it gets quite easy.

Warm visco rating of 40 in your area seems reasonable. A good 30 will evidently do fine as well. This is the relevant rating when driving.

A high Winter rating doesn't do as much when the oil is warm but makes for poor lubrication on cold starts. See previous comment about stability. Mostly relevant for hard driving. These engines don't really do hard driving that actually wears hard on the oil since the car won't really allow it when it comes to things such as handling.. towing would be an exception.

There's no reason to choose a higher winter rating than needed to reach the desired warm rating and stay within recommendations.

And really if the car has been fine this far with 5w30 it'll be fine for long enough for something else to kill it.

Just my two cents.

[MoVolvos]

Reduced flow is a big contributor to engine sludge. All this points to thinner oil. Synthetic oil has greater viscosity stability and does not gain viscosity with use in engine so that is the recommendation for older engines and a requirement for newer models.

Thinner does not always equate with better protection or potentially flow. I would not use any other 15W-40 except for Swepco for that reason. You are not far from them. Not sure if they provide tours but maybe one of these day? I use to use the 306 15W-40 for all my cars but switched to 308 5W-40 till I accidentally use the Rotella T6 5W-40. The sale price was so low I thought I purchase some regular oil. Though the Swepco makes the cars run better I can't afford it even though both can go 10 to 15K between changes. I've done that a couple of times .

https://www.google.com/maps/dir/Ponder, ... 32.7652843

[MoVolvos]

Texas being warm most of the time 15W40 is heavier for older looser motors with more miles. The engine is quieter besides peppier. That was the weight for many many years till I purchased the 98 S70 T5. Too thick during start up for cooler weathers and the Turbo.

I've got a newer car that's barely broken in yet so I stick with 5w40. Happy turbo and no oil consumption.

Agree, also 5W-40 allows the owner to have one oil for their entire fleet.

[amblerman]

I've also found that chart strange.

In particular, I found it confusing that the xw-30s cover different high end temperatures ranges. They are supposed to be performing like a xW-30 at operating temperatures.

I agree with Rattnalle when he says "An oil with a smaller span between cold and warm viscosity is in theory more stable and thus able to resist heat better long term. In practice I suspect it varies quite a lot."

However, it'd be surprised if there was much of a significance difference with top brand modern xW-30s especially in the "full synthetic" lines. I mean according to that chart, we shouldn't even consider a 5W-30 if the ambient temperature is higher than 68 F? A nice spring/fall day? I find that hard to believe.

for the last 3 years I've been using various 10w-40, 5w-40, 10w-30 and 5w-30 based on how I rotate my oil stock. Then again mine is a non-turbo s70 which I'm sure is pretty easy on oil in general.

[Rattnalle]

I think it's worth keeping in mind that oil chart is quite old by now. Oil classification comes into play too.

[amblerman]

I think it's worth keeping in mind that oil chart is quite old by now. Oil classification comes into play too.

Oh yes. I just looked up the owner's manual for my 1999 s70 and the spec it calls for is for "SG, SG/CD, SH" .
That's ancient at this point and obsolete. I was expecting my manual mentioned SL but I guess not.
_A

[Rattnalle]

I think it's worth keeping in mind that oil chart is quite old by now. Oil classification comes into play too.

Oh yes. I just looked up the owner's manual for my 1999 s70 and the spec it calls for is for "SG, SG/CD, SH" .
That's ancient at this point and obsolete. I was expecting my manual mentioned SL but I guess not.
_A

We're using the ACEA system mostly here but it's sort of similar in that the for my -04 recommended A2 oil isn't available anymore and the A3 for heavy driving is the new base level.

[CSDentonTX]

Yes, bottom line is most name brand oils will perform better today than those when our car was built. Manual says "SG, SG/CD, SH or ILSAC GF-1", but most oils on the shelf are at a API SN ILSAC GF-5, (although I have seen some marked SM and supposedly still current but for engines made before 2010). And there's SP (GF-6A/B) coming soon.

See also
https://www.motor.com/2019/05/get-ready-gf-6-motor-oil/

One thing is for sure is that oil is getting better and better generally.

[lummert]

I think you'll find that heavy duty diesel engine oil has a lower pour point than one would assume. Rotella T5 15W-40 Synthetic Blend heavy duty diesel engine oil has an even lower pour point. Remember that huge diesel engines are harder to start in colder temps. The specs for these oils are available with a bit of searching.

[Rattnalle]

I think you'll find that heavy duty diesel engine oil has a lower pour point than one would assume. Rotella T5 15W-40 Synthetic Blend heavy duty diesel engine oil has an even lower pour point. Remember that huge diesel engines are harder to start in colder temps. The specs for these oils are available with a bit of searching.

Lorry engines are designed completely differently so it's not a relevant comparison.