quickersilver

I did a bit of research, and discovered that 5W40 could be less than ideal for high temperatures and/or high-performance driving. Apparantly, they have to add more polymers to low-weight oils to give them the characteristics of higher-weight oils; i.e., a 10W40 will require more polymers than a 20W40. From what I read, oils with higher numbers of polymers are more prone to thermal breakdown and so forth, and can result in sticking rings...it definitely sounds like those of us who live in warmer climates and like "spirited" driving would be better off with a 20W40, etc...

Comments? Here's the page I got my info from...

http://www.iaw.com/~aubertin/sho/tech/oil.htm<p>'00 S4
Silver/onyx
6-speed, convenience, Bose w/changer,
cold weather pkg, unchipped
Valentine One :-)

captainbilly

The only problem is poor lubrication/flow when the engine is warming up. The synthetics don't have the breakdown problems that you mentioned (at least not in 7,500 miles between changes) but they are expensive. I use 5-50 synthetic to get good cold flow and good high temp viscosity. I ran a test some years ago and found that Castrol GTX 10-40 showed significant breakdown in as little as 1500 miles while 10-40 Mobil 1 didn't show any after 10,000 miles (I wasn't willing to leave it in my car for more than 10k although at the time they were suggesting that you could leave it in for 40k). I used low RPM oil pressure as my indicator of viscosity loss. The car was a high performance Datsun (Nissan) 510.

quickersilver

<p>'00 S4
Silver/onyx
6-speed, convenience, Bose w/changer,
cold weather pkg, unchipped
Valentine One :-)

hwj

Joe Aubertin's SHO web site is one of the better ones out there done by an individual owner. I remember surfing there many a moon ago.

Another warning about oils with a large viscosity spread (from another SHO site, even) is <a href="http://www.shotimes.com/SHO3synthoil.html">here</a>. To save you the click, here's what Gary Morrell, a senior Ford engineer involved with the SHO product line, had to say:

<i>"5W-50 is an awfully wide viscosity spread, even for a synthetic. Castrol must be using a large amount of viscosity modifiers to get this spread. Viscosity modifiers (VMs) are long chain polymers that are added to a light base oil to prevent it from thinning excessively as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as the 'X'W number indicates. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. Unfortunately, VM's will shear over time, reducing their effectiveness, and can burn and form deposits that cause ring sticking. Most manufacturers have shied away from oils with more than a 30 point viscosity spread. Notice how hard it is to find 10W-40 anymore? For awhile, GM threatened to void warranties if 10W-40 was used.</i>

<i>AMSOIL uses no VM's in their 10W-30 and 15W-40 weights, and Mobil 1 formulates their 5W-30 and 10W-30 without VM's. Oils that start out with heavier base stocks, such as 15W-50 and 20W-50 need very small amounts of VM's, however, I can't recommend either of these 2 oils if your wintertime temperatures go below 30 deg. F.</i>

<i>Try to keep the viscosity spread under 30 points, this will keep your bearings happy."</i><p>--
Hugh
<a href="http://home.austin.rr.com/hwj/hwj/cars/s4.html">'00 S4 Nogaro/Onyx+Blue</a>

RENN 951

<p>John G
00 S4 Silver/Silver
99 A6 Avant Brilliant Black/Vanilla-Onyx

Just a stock S4

I'll bet against it. Doesn;t exist :-)

quickersilver

What I _meant_ was.... ;-)<p>'00 S4
Silver/onyx
6-speed, convenience, Bose w/changer,
cold weather pkg, unchipped
Valentine One :-)