John Wilkinson

This is exactly why I don't trust my service department, or any other on this issue. Every mechanic you talk to has his own opinions about which oil to use. One says 5W-30 for 1.8T and 15W-50 for 2.8, another the opposite. Your mechanic recommnds higher-viscosity oil to eliminate valve noise, mine says lower viscosity.

This either proves that most mechanics are incompetent, and that there are going to be a lot of prematurely worn engines around in five years, *or* that your choice of oil doesn't really matter much. If the latter is true (and I suspect that it is), I'll take the extra power and economy available with 5W-30.

John Wilkinson

Sounds great! Thanks for the input; I'll be submitting a revised version soon.

JSC

One reason my friend/ Porsche tech recommends the 15W50 is the greater thickness that adheres to the cylinder wall (pardon the lack of technical engineering jargon)... I was there one day when a customer who I knew from PCA came in in his 944 (w/ Mobil 1 15W50) after his water pump died and dumped all his coolant. He drove a significant distance with no coolant and had no engine damage. Whether 10W30 would have given similar protection we can't know but the opinion was that the 15W50 gave an extra margin of lubrication on the cylinder wall to help avoid catastrophic results.

Just an anecdote. We are, of course, all right and we do whatever makes us feel best.

Kevin K

If one anticipates he may have to drive w/o coolant, perhaps a belly full of SAE 250 gear oil is in order, since oil temps will be 50+% higher than normal. That way, he could drive even faster with no coolant, and longer. No way 10-30 could do that.....

ChuckH

...best for your car! Seriously though, by the time I sold my 90Q at 109K miles, I had tried several different weights and brands. The A4 2.8 has about 25K on it now. Here are my own observations, not taking into account my mechanic's opinions.

90Q had least startup valve noise with either the Mobil 1 10W-30 or the Mobil 1 15W-50, meaning that it almost never clattered at startup, or only for a brief moment. Kendall 15W-40 Dino oil was very good in this respect also, and is what my mechanic uses as standard fill for most of his cars. The difference between the Mobil 1 10W-30 and the 15W-50 was mostly with hi temp and consumption. The valves were a little more noisy (though not clattery) with the 10W-30, and the consumption was about 1 quart for every 1500 miles, where the 15W-50 brought that up to about 1 quart every 3000 miles. At one point I decided to try Redline 10W-40 as a compromise. Big mistake! At several cold startups, the valves would clatter for several minutes, really embarrassingly loud, and after about 1000 miles, I was down a quart. At that point, I started mixing in 20W-50 Redline everytime I needed to add. After about three quarts of that (a filter change in there also), the valve noise went away.

Now, with the A4, experiences have been nearly the same, although Redline has not (and probably won't) be used. Have not even tried the lighter Mobil 1, but Mobil 1 15W-50 gives less noise and less consumption than Dino 10W-30 or 10W-40. Mobil 1 15W-50 goes at a rate of about 1 quart every 3K miles or so (just like 90Q), while the others go about 2K miles per quart.

I don't think I've ever actually looked at the A4 manuals recommendations, but for the 90Q, 10W-30 or 10W-40 oil is only recommended for cold climates and not for extended driving.

Strangely, Nissan recommends 5W-30 for my new Xterra, which seems light for a truck. However, I plan to follow that recommendation using Mobil 1; atleast initially.

The reasons I've heard for using the lighter oil in the 1.8T are for the turbo itself. Supposedly, it is better to have fewer viscosity extenders to reduce buildup in the turbo, or something like that! Also, the lighter oils will flow faster to the turbo for lubrication, although this is less of a factor with synthetic. A 10W-30 oil has fewer viscosity extenders than a 15W-50. Someone here can explain this in more detail, but I can't remember who it was.

So, that's how I feel about it! Obviously, if you're going to be in severe cold, you'll want to go lighter. Otherwise,...??? Like you and others have said; everyone has an opinion. I am one who will try different things and see what seems to work best for my particular car. I don't think it's coincidence though that the two Audi's seem to favor the same blend! Just my opinion! :-)

Charles

ChuckH

...hard, all the way to redline frequently (was especially true of the 90Q). Those doing frequent cold starts, and who never heat up their car, may want to go lighter. Many things can be a factor, and what's best for one person may not be the best for another.

ChuckH

...a 10W-40 that is available in certain markets. I have been wanting a 10W-40 from Mobil 1 for a long time, but it's not available here. A 5W-40 would also be a good alternative, and it really surprises me that Mobil 1 doesn't offer all it's options in all the markets. To their credit, all their products offer superb protection for both cold and hot, so really I don't think you cna go wrong with Mobil 1.

John Wilkinson

Driving at higher rpms is actually a easier on the oil than driving at lower rpms. The higher shear rate causes thicker films to form, assuming that your oil is reasonably shear stable -- as all SJ oils are. Lack of shear stability at high rpm operation may have been a concern with earlier multi-viscosity oils which had much inferior chemisty for their viscosity modifiers. As for high rpm stress on the other parts of your engine...

Seriously, how hard you drive shouldn't be a consideration unless it significantly raises your oil temperature. With most people who spend time at the tack reporting that their oil temps hardly budged, I don't think that even the hardest street driving could be cause for concern.