Serious discussion about oil

[Red2000GT]

I figured that since the engines been apart it'd be a good idea to do an oil change. Now normally it's just a chance to spend a little quality time with the car,check for leaks of any kind and give the underside a once over. While i was at Canadian Tire grabbing supplies i saw that Quaker State makes a line of oils for different applications. They have a 5w30 for "regular" driving,10w30 for "heavy duty" apps like towing and such,then a 15w30 for "high performance" driving. I've always used 5w30 cause that's what Ford recommends so i loaded up and headed home. BUT,while i'm under the car,waiting for the oil to completely drain i got thinking about the QS ratings. At first it seemed weird to me to make a heavier weight oil for performance applications. By all sense,the lighter weight should free up more hp from less drag,which is what a "high performance" car owner wants. So why would 15w30 be better? Here's my best guess. A heavier weight oil maintains a better "cushion" between the metal surfaces at higher rpm. BUT,looking at the ratings ?w30 they should all be the same viscosity from ? temp to 30 degrees and as we know an engine runs a little warmer than 30 degrees C. Typical oil temps for most cars without an oil cooler will be within 30 degrees of the engine temp.(about 165F or 74C on a mustang) So wouldn't it make sense that all the oils will be the same viscosity at 74C,or are there still some differences?
I also remember seeing that alot of race teams use a single weight oil in their engines(seems to usually be a 40 or 50 weight). Is this for the same reason,to maintain a more stable oil film on all the bearing surfaces when running at constant high rpm? I think we all know that mineral oils versus synthetic is not the issue here(no question that synthetic is better) but i'm really wondering if someone,like myself,who drives their car hard would be better with the 15w30 oil to protect the engine? Keeping in mind that i don't winter drive it so a light oil is not crucial for easy starting.
What's everyone's opinion's on the subject? Am i on the right track with my thoughts on the 15 vs 5 w30 ? Any experienced engine guys who want to speak up please do as i'm really wondering what your using and why?

 

[WOT]

I don't know of anyone running a mod motor with anything heavier then 30w oil. The clearences inside the motor are just too tight. When I had mine apart all the clearances were on the bottom end of what was allowable.

Running a heavier oil will give higher oil pressure but it also won't flow as well as a lighter oil.

The "w" rating is also for the weight of the oil gets hot. All oils are rated at 100*C.

You can check this out.http://www.carbibles.com/engineoil_bible.html

 

[SPEED FREAK]

I don't think you need to worry about anything more than 5w30 unless you never start the car on a day less than 20*C outside (really hard on the oil pump in the cold) then you can run the 40-50 weight oils they help alot at higher rpm (7 - 10,000ish) by providing a more stable cushion between the surfaces.

 

[TweekedGT]

Oh boy, this could be a real long discussion. i will through my .02 in since i've just completed a course on this very subject. Basically there is an application for every oil. For our vehicles the best oil is a Mobil 1 synthetic 0w40. It is better for start up in cold conditions, transfers heat well and because we are over head cam cars it is easy to transport to the heads and cams. The synthetic is the most important part, all the molecules are of the same size and there are no perifins in the oil to degrade and to break down. There a re companies that call their product synthetic even thought they technically are not, they have just hydrocracked the molecules. Courts in the US and Britian have allowed the use of the word synthetic for some brands because there has been a physical human intervention that has change the chemistry of the oil even though it is still mineral oil. Just trust me on this, use Mobil 1 synthetic 0w40 oil. I could really bash some brands badly here but won't. I have no interest in Mobil/Esso just they have proven through many independent studies to be the best. In all of our oilfield equipment we use 0w40 in every component of the unit, transmission, hydraulics, differentials, it is amazing stuff.

 

[Red2000GT]

That's cool,I run 5w30 Mobil 1 all the time. A few bucks more but always seemed to be worth it.

 

[Red2000GT]

I don't know of anyone running a mod motor with anything heavier then 30w oil. The clearences inside the motor are just too tight. When I had mine apart all the clearances were on the bottom end of what was allowable.

Running a heavier oil will give higher oil pressure but it also won't flow as well as a lighter oil.

The "w" rating is also for the weight of the oil gets hot. All oils are rated at 100*C.

You can check this out.http://www.carbibles.com/engineoil_bible.html

I didn't specify but the race engines i'd seen runing the single weight oils were all traditional pushrod motors.
Also,I didn't know about the hot temp rating. You learn something new every day.

 

[Red2000GT]

So my question is,why does QS rate their 15w30 for high performance use?

 

[TweekedGT]

So my question is,why does QS rate their 15w30 for high performance use?

Traditionally on pushrod motors racers use 20w50, the damn stuff is like glue. A lot of engine builders have broken in motors with that stuff too. Because the cams and rotating assemblies on pushrods are so low in the motor it doesn't have to flow very far to lubricate the internals. On newer cars overhead cams have become very popular which doesn't work well with the old 20w50 or 15w30. Those thick viscous oils just stays in the passages longer. The problem for daily drivers is start up. Try turning a car motor over on a cold day with that stuff, brutal on your internals even if you can get the car to turn over. 15w30 in this country would be a huge no-no. if you were running a pure race car creating major heat and thin ning out the oil you may be ok but i wouldn't want my oil pump pushing that sludge through my motor.

 

[Red2000GT]

I seeeeee.......

 

[TGJ]

That's cool,I run 5w30 Mobil 1 all the time. A few bucks more but always seemed to be worth it.

Good, and don't stop using it as that is the oil you want.

I would never ever run more than a 30W oil in a Modular Ford V8/V10. The reasons have already been said.