Get a gauge on that engine. Then let us know what pressure you have when the engine is good and warmed up and idling and what it is cruzing at 2500 or 3000 rpm. My well worn 160k 350 needed 10w-40 to get 10 psi at idle. If I were driving highway in the middle of summer it preferred 15w-50.
I use 15W50 in all my carbed v8 cars. (used to use either 20W50 or 10W40 depending on time of year). However it is dependant on how you use the car. I use my car only in the summer where the temp is never below 25* C. If i drive my car late into the fall (like late september/early october, i would switch over to 10W40). This past year i didnt change back to 10W40 in late fall, and noticed the tick as well on startup. I prolly will be more diligent on changing it next time. 15W50 first number tells you how viscous the oil is at startup (cold), the second one tells you how viscous it is when hot. Generally speaking though, once the engine warms up, all viscosities will be the same. If you drive in cold environment, you want the first number to be as low as possible. If you are demanding of your engine in hot environment, you want the latter number to be as high as possible. There is no reason for the first number to be that high really, unless you are dealing with worn bearings or leaky seals. But the 15W50 is a trade off oil. If there was a 5W50 or 10W50, id be using that instead.
IMHO there is no reason to use a viscosity any higher than what is necessary to achieve proper oil pressure. The higher the viscosity the longer it takes at start up to start circulating & start up is when most engine damage occurs. Unless the engine sees continuous extreme duty where the oil gets extremely hot (eg: high speed trailer towing ion a hot summers day) or ambient temp is over 100*F, it is not necessary to go higher than 10w30 if your engine is in good shape. Buick recommended a max viscosity of 20w40. Too high a viscosity will reduce performance & economy and can harm the engine.
Ouch !! An "oil thread" ... these are like "Ford vs Chevy" threads. Spend some time and read this, please: http://www.carbibles.com/engineoil_bible.html .
So it sounds like the Mobil 1 15w40 has high levels of ZDDP still. Looks like I know which oil I'm getting for my next change. Thanks for posting that link MJT.
??W50 is really to thick an oil for our engines. i think the owners manual stipulates 5w?? to ??w40. i use castrol gtx 10w40 + zddplus.
I would only use a 50 wieght on forced inducted engines 1ow30 will do you well 5w30 or even 0w30 would be great also..just usualy a bit more pricey per quart