I run 15w-50 in the summer. Excellent for hot running engines - especially turbo equipped. A 2.8 engine will not really benefit from this weight, as its temps will not reach the point where the oils better viscosity is taken advantage of.

But DavidK does have a point - if you have modified your N/A engine then you might see some use in a 15w-50. But running 0W-30 wil NOT hurt a high horsepower car. I know plent of guys with K04's running a 0w-30 or a 0w-50 oil.

It's the 2nd weight number that counts for heat, people. A 10w-30 is no different than a 0w-30 in the summer. The 10w comes into play when the ambient temperatures fall and you engine must run/start-up with cold oil for a while.

 

I think we've been saying some of the same things brrman, and I agree with your summary, but I don't agree with your first statement.

I don't know if you can unequivocally say that there are some engines (you cited the 2.8) that will not benefit from the 15w-50 oil viscosity - especially in the context of this thread. In summer (in the U.S.) I believe that all automotive engines can benefit from a higher viscosity to offset the higher ambient temps - they clearly can reach full core working temperatures, so the additional stress to maintain safe (read: moderate) working temp levels is better managed by the higher viscosity.

If you have other evidence contrary to this, I'm open for further enlightenment.

 

Don't equate higher viscosity with better protection. It doesn't always work this way. Todays engines have tighter tolerances and they are nothing like the engines of yesterday. There's a reason that the 3.0l's factory fill is Castrol Syntec 0W-30. Increasing the viscosity to a 15W-50 just increases friction/heat in the engine due to it being "thicker", "heavier" and more difficult to flow/pump through the engine. 0w-30 oils will adequately protect the engine and keep the oil temps/friction in check.

The 15w-50 is better for hotter engines because the hotter temps achieved in engines like the 1.8t will allow the oil to thin more than a 2.8 would as it reaches running temp. So what I am saying is that a a 2.8 will not benefit from 15w-50 over a 0w-30. The 15w will not thin as much as it should and will therefore be thicker in the engine and cause more friction and resistance.

 

I follow your argument brrman, and I agree with some of your statements, but I don't agree with some of your key points.

Your last statement: "The 15w will not thin as much as it should and will therefore be thicker in the engine and cause more friction and resistance" doesn't make sense to me at all.

The first part is true; the 15w will not thin out as much as a 0w, but what do mean, "...thin as much as it should"??
Furthermore, a thicker oil will not cause more friction.

Lastly, you quote, "...the hotter temps achieved in engines like the 1.8t will allow the oil to thin more than a 2.8 would as it reaches running temp" is very odd to me. Both the 1.8t and the 2.8 will reach running temps over a different time interval, but both will eventually run at the same temps (all other factors being equal). Both the 1.8t and the 2.8 run at (relatively) the same running temps. (Therefore, both engines can benefit from a high viscosity oil, provided conditions demand it.)

My argument isn't in these facts. I suggest that the warmer ambient temps and the "performance" of these engines would benefit from an oil with higher viscosity; the net higher heat values are well utilized by the oil's higher viscosity.

It should be noted that the context, for which I have been making these comments, has been for our Audis being driven as performance vehicles NOT as daily commuters. As daily commuters it would be a waste of viscosity - even in the heat of the summer.

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For further emphasis...........
Viscosity is the property of an oil to develop and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. At high temperatures, an oil with too low a viscosity can shear and loose film strength. At low temperatures, an oil with too high a viscosity may not pump to the proper parts, thus, the film may tear at high rpm.

By the way: The Department of Environment and Natural Resources did an oil viscosity study in 1996: Their laboratory tests measured the viscosity of oils under high-temperature, high-stress conditions and found essentially no flow rate differences between low viscosity oils and their high viscosity brand mates. But at low temperatures, the low viscosity oils flowed more easily.

 

Whoa! You guys know your stuff and can do research. On the other end of the color spectrum, my thought is that a lighter weight oil would be easier for the engine to "push" through. Although you could run a heavier weight oil at maybe 1/2 -1 quart low. Maybe this could give you a couple of the "Power of Suggestion" horsepower. hehehe

 

Your right in one aspect. A lighter oil is easier to push. The oil pump does not work as hard to move a lighter viscosity, thus the oil pressure is lower than that with a higher viscosity. It doesn't really (directly) relate to or reflect in horsepower though. There can be a theoretical argumant made for the higher oil pressure generated by the higher viscosity oil, but, in practice, the difference is minimal and does not have any real world affect on the engine.

On the other point... Just because an oil has a high viscosity, it does not give one the freedom to reduce the overall capacity (volume) of oil within the crankcase. It doesn't "spread" out, as you might hope, as it gets hotter. It maintains a certain atomic viscosity once it is warm. Therefore, the engine would be under the same stress as if it were low on oil of a lower viscosity.

 

Im gonna chime in here alright Imola you said

Lastly, you quote, "...the hotter temps achieved in engines like the 1.8t will allow the oil to thin more than a 2.8 would as it reaches running temp" is very odd to me. Both the 1.8t and the 2.8 will reach running temps over a different time interval, but both will eventually run at the same temps (all other factors being equal). Both the 1.8t and the 2.8 run at (relatively) the same running temps. (Therefore, both engines can benefit from a high viscosity oil, provided conditions demand it.)

this is basicaly true but I think what Brrman was refering to is performance driving (Not to put words in anyones mouth) when you push the 1.8t hard the exhaust manifolds glow thusly heating the turbo and the oil therein which is why under some situations in a 1.8t the oil temp can spike at 300 degrees Im not completely sure but I doubt the 2.8 NA engine oil ever safely reaches this temp which is the reason I run 15w-50 in the summer because of the heat spikes caused buy the turbo

 

No, in fact, if you re-read my posts I make the clarification that the context, by which I am referring, is about perormance driving or driving under heavy/severe/hot conditions. Therefore, comparatively, any engine subjected to performance driving in warmer ambient atmospheres will benefit from the higher viscosity oil. To the point, I do believe the 2.8 engine (under the driving conditions as stated earlier) can reach higher working temps and benefit from a higher viscosity oil. Lastly, as you stated quite well, the spiking of engine heat can benefit from the higher viscosity - any engine (the 2.8 included) can easily encounter loads that will cause heat spikes.

 

Im not disputing that but what Im saying is that the 1.8t has more NEED of higher viscosity oils... where basicaly arguing the same point here.

 

Yeah... true... right... OK!

I'm not even arguing with you, but yeah, the 1.8t may have a greater need, but I think brrman was claiming that the 2.8 does not need the higher viscosity oil.

I think (if I read his comments correctly) he was going so far as to suggest that the higher viscosity oil would not be beneficial to the 2.8 engine at all - under any circumstances.

If that is what he was claiming, then I am of the opposite opinion.