Darryl W

The manual recommends 10W-30 in the A4 1.8T, but should I be using the 15W-50, really? I figure that synthetic 10W-30 should be good enough protection for my turbo, even in the summer.<p>Does anyone think this is dangerous?<p>Darryl<br>98.5 1.8t qms

T2

Whether an oil is synthetic or not will not change its viscosity characteristics as a function of normal operating range. A 15W-50 normal and synthetic oil will flow the same at 0 and 200F - that's what the oil weights mean. Now, I do agree that the synthetic won't break down, out gas, coke-up as much... My opinion.<p>Tom<br>1.8TQMS Silver/Ecru

T2

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Big O

Now, you're right, I know the weights are supposed to reflect the viscosity, so what exactly indicates the better flow of the synthetic at low temperatures?<p>I'm entirely in agreement with you, though, I'm just wondering *where* and *how* the viscosity index is measured. At a particular temperature? Across all temperatures? If so, what explains the flow differences between synthetic 15W and regular 15W at extremely low temps?<p>My understanding was that the different molecules in the dino oil act differently under extreme temperatures, including the paraffins (waxes) which make the oil "clumpy". Since dino oil is "refined", i.e. it's the best attempt at selecting a particular molecular property/structure from a wild (naturally occuring) mix of molecular lengths, it invariably contains some residual paraffins. Synthetic is "made to order" (from homogeneous substances), it doesn't have these residuals.<p>Hey, where's that Organic Chemistry book . . ?!?

Big O

We can discuss this until we're blue in the face, but if a sudden mishap drains three of the four and a half quarts out of my car, if I miss a shift and wrap the crankshaft into bearing-scoring territory, or if my wife overheats the engine before noticing something pierced the radiator, I'll take the oil that provides a Kinematic Viscosity rating of 18.0 cSt (15W-50) over the 9.7-10.0 of the lower weights at 100 degrees C every time! <p>Please note, this is NOT intended to say you're wrong, just that I like to have that extra layer of protection. There is a reason they recommend it for "high performance engines" and "racing duty".<p>The normal loss of pumpability experienced with paraffin-containing refined oils is not as prevalent with synthetics, so it pumps better than most normal 5W-30s. For that matter, the 15W-50 synth pumps better at -25 than the 0W-30 at -40.<p>Granted, if I were to leave the A4 sitting at the arctic circle in -90 degrees, I'd use the thinnest oil I can find. But ours sits inside and isn't exposed to the winter cold any longer than three hours at a time, so the risk of the block ever getting to under -25 degrees is miniscule. But an hour into a nice, hard run using the G-tech and/or racing around a road course, and the oil and turbo will be just about as hot as they are on an average summer day. At least that's what my gauge says.<p>Sorry if I seem so **** about this; I just recently got into this discussion with my father after he blew up his tractor and then almost seized his Audi because he runs them VERY low on oil (he uses the oil light and/or lifter tick as an oil change indicator) and won't listen to my advice on giving up on the straight 30W oil ! :-0

Mr. Alzheimer Big O

I know it's manufacturer blather, but it does *not* compare it to the cheaper product, just to the *other* viscosities, so they have no incentive to sell you the heavier weight over the others.<p>http://www.mobil1.com/oneracing/about/products/engineoil/15w_50/index.html<p>Note that it states "less oil consumption", which is one of the reasons I have kept my faith! That one I could measure and prove!<ul><li><a href="http://www.mobil1.com/oneracing/about/products/engineoil/15w_50/index.html">Mobil One Spec Sheet for Synthetics - Good Stuff !</a></li></ul>

T2

I think the following is correct... The W number is the viscosity index for the oil at 0F (-32C) and the 2nd number is the viscosity (weight) index at 212F (100C). Each weight of viscosity index represents a range of actual viscosity. Therefore a 15W-50 oil is actual THINNER (lower number) at 0F than at 212F. You want it to be thinner (I think) because you don't need the protection (cooler temps) but you do need to get the oil to all of the places in the engine as quickly and uniformly as possible. At higher temps, you need the protection that thicker viscosity brings. Now at extremely low temps (less than -10F) synthetic has a BIG advantage - its pour point is much lower than typical nonsynthetic. The data I've seen (can't recall the website) shows that most synthetics pour point is below -50F while for many normal oils its no lower than -10F. That's where the synthetic nature of it helps a lot. Hope this helps.<p>Tom<br>1.8TQMS Silver/Ecru<p>

Larry R

At least according to my dealer, the information about oil weight in the Audi manual is incorrect. The car needs heavier oil than the manual indicates. I haven't actually called Audi myself to confirm this, but he says that he did. Why doesn't Audi reprint the manual? Who knows?

Graham

The last oil I put into my qT was Mobil 1 5W50, widely available even from Kmart and Target here downunder!!<p>Graham

Graham

They may not sell it in your neck of the woods, but they do make it as I have it.<p>Graham