On misconception with motor oil is how thin it is. Viscosity has no bearing on molecule size and will not tell you more than an oils ressitance to heat and pressure. You can have a natural oil at 10w-30 and a synthetic 10W-30 and see more burnt or used oil due to the fact the sythetic oil is size controlled on a mollecular level which tend to allow it in places conventional oils may not seep .. this could be between rings, through valve seals or any gasket for that matter. Another factor to consider as well is that conventional oils are about 70 carriers and 30 lube and sythetics are about 30 percent carriers and 70 percent lube ... which tend to lend to high ash content in your oil in loose tollerance motors or motor with excessive crankcase pressure.

All in all, should be ok to run sythetics or naturals just dont expecet life changing benefits. A good oil natural or synthetic is a fresh oil changed with frequency and diligence.

I only run Royal Purple and vary viscosity based up on use .. non/light nitrous 10w30 and 15w40 for heavy track use, but it 'cause i get it for $2 a quart

 

I think its unsubstansiated to say seals will leak with simply putting in synthetic oil. Oil seals leak anyway at high mileage, on my old '01 S10 the crank seal started seeping at 10k.....
Far as switching to 15w-50, I wouldn't do so. 15 is too high for cold starts, and yes their is a defiable differance between 5w30 and 15w-50. And thicker oil causes the engine to wear faster.
On Toyota Prius(s) i've seen a DTC for "hard start" from 10w-30 instead of the manufacture required 5w30. I think these issues will become more profound once 42v electric motors/gas motor vehicles become prodominant.

 

GM reccomends that the Gen III motors (other than the LS6 for some reason) use regular old dino-oil.....I'll stick with the GM reccomendation

 

hmm... where did u hear this? manual?

 

owners manual, GM techs at my dealership, EVERY oil change place I have EVER been to (I wanted to run synthetic but was told GM reccomended dino-oil)

 

I changed to Mobil 1 today. I told the guy to put 5w30 in it. Hey said he misunderstood me and put 10w30. Oh well. No huge difference, seems to run smoother, especially in the high rpms. I'm happy with it though. Just my .02

 

FullfloatingHD

You are right that merely swithing types of oils will not 'cause' valve stems to seep or leak but if a motor has mileage and some wear and tear it will be more suseptable to leakage with a molecularly smaller oil. As far as my running 15w40, it primarily due to the fact my 30,000 miles on the odometer are turned by over 200 bottle fills of nitrous ... needless to say my internal motor tolerances are a bit looser than most

 

im running royal purple 5w30 in my 02 5.3 silverado. before i ran valoline 5w30 fulll synthic in it. i deffently seen improvements over the valoline oil. royal purple nothing else in mine truck

 

As I pointed out earlier that valvoline full synthetic is just another "Group 3" mineral oil with some chemical altering. And Royal Purple, I have never tried it but talk to Patman for his impression of it.