Best oil for 87 328 GTS located in Southern California

For pure street driving (adult style) thin 5W-30
For back road driving (agressive) thick 5W-30
For track driving (Drivers Education) thin 5W-40
For track driving (real racing) thick 5W-40
For track driving (endurance racing) 15W-50

Unless the oil temperature guage goes above 260dF there is no particular need to go thicker than a medium 5W-30 oil (viscosity ~= 11 cSt).

The xW-30 grade runs from 9.6 cSt through 12.4 cSt at operating temperature. A thin xW-30 will run 9.6 through 10.5 cSt, and a thick xW-30 oil will run from 11.5 through 12.4 cSt. With a 5W cold startup specification the thinner oils will be in the 65-75 cSt range at startup and flow much faster to the vital engine parts that your typical 10W-40 spec oils (80-100 cSt at startup). This reduces wear during the critical first minutes after startup where (for most cars) 85%+ of all engine wear occurs.

Then with the caveat of not "getting it on" until the oil gets into the 160dF range you can expect a long healthy life for your engine. And if the temperature guage never gets above 260dF you will always have 4.5 cSt of operating viscosity -- which is plenty to support the various loads inside the engine.

But let us say you ARE encountering oil temperatures above 260dF. At this point, you should change what you look at in the oil specification from the SAE grade (xW-yy) and look at the HTHS specification. For operating oil temps at and above 260dF you should be using an oil with at least HTHS 3.6 for temperatures above 285dF you should be using an oil with an HTHS above 4.1. The operating viscosity spec is for oil at/near the 212dF range and is not applicable at the 260dF+ range. HTHS is measured at 302dF under conditions of high shear -- which is close to the punishment the cams assert on the valve train at near RedLine temperatures.

Now, all of this should be moderated with a statement about oil consumption. If you are getting less than 1000 miles per quart you should consider increasing the oil grade by 1/2 step (thin->thick in same grade:: thick grade n->thin Grade n+10). So if you see consumption issues with a thicker 5W-30 you should first try a thin 5W-40 (or 10W-40) oil before going a whole step to thick 10W-40 oil.

Finally, I have noticed that on my F355 that when the dry sump is above 1/2 way between max and min on the dip stick, that oil consumption is visible. But when the oil gets to the 1/2 way point, on my car, oil consumption basically goes to zero. This is a known characteristics of dry sump oiling systems. When the oil level is high, it is rather easy for the escaping gasses to carry oil into the intake system and be consumed in the engine. As the oil level gets to where the designers want it, this slows to a bare crawl. So, don't overfill the dry sump, and/or don't confuse oil consumptioin at high oil levels with oil consumptioin at lesser overfill levels.

With 50K miles on the clock, and 4K miles on race tracks under its belt, my F355B still does 2000 miles/qt from 1/2 way and on down on the dip stick.

If (and when) my car gets taken of the "always track ready" status, I will be running a 5W-30 oil. As it is, I am running an oil with an HTHS of 3.6 which just happens to be 5W-40 M1 T&SUV (which has resently changed its name to 5W40 Turbo Diesel Truck oil and T&SUV has been downgraded to 5W-30 automobile oil.

I am a big fan of thinner at startup and watch the temperature guage to determine the correct oil for most applications. I am also a big fan of rather short oil change intervals. For me this tends to be after one track day or 4K miles when no track days have transpired (and never more than 1 year). I only use top quality synthetics but I am rather nonpartial to any particular brand (M1, RedLine, AMSoil,...) as long as I can get the MDS sheets and find what they spec the oil at, I can make an informed judgement.