Originally Posted by pizzaguy
These questions are for anyone who KNOWS the answers.
1) Ok, so why the 0 weight oil anyway? I mean, my 85 truck called for 10W30 and my 1993 truck called for 5W30 and now the car calls for 0W40... why this trend? Why are manufacturers calling for thinner and thinner oils?
There are several reasons for this:
First off, Fuel Economy is the number 1 reason.
A lighter weight oil is easier to push through the engine, and requires less power to push through the motor when cold, and warming up to temperature. This allows Honda, Ford, and everyone else who puts 5W-20 weight into their small little 4 cylinder cars to get 30+ mpg during EPA testing.
Second, HP is the second reason.
As I said above, a lighter weight oil doesn't rob as much hp from the engine.
This allows a manufacturer to say their car has a 1 or 2 hp advantage over the same engine that used the heavier weight oil.
Third, proper function of variable cam systems.
Some car companies have very sensitive camshaft adjusting mechanisms, like Porsche, and if you put in too heavy an oil, the cam advancing functionality is delayed, which then sets off a CEL. If the cam advancing action is delayed too much, you risk having the valves hit the pistons at cam changeover points. Porsche then sends off your oil for testing, sees that you have the wrong weight oil in your engine, and denies your warrantee claim.
Fourth, and my final argument is cold start protection.
As I've implied before, a higher first number is a thicker, heavier oil.
This requires that the engine work harder to push it through to all the points in the engine. Also, this higher pressure from the thicker cold oil will force the bypass valve in the oil filter open, allowing cold, heavy, dirty, contaminated oil into your engine, accelerating wear. So you may think you are protecting your motor better, but in reality, you're not.
2) Why the recommendation for synthetic oils?
Synthetic oils are capable of handling higher temperature environments without breaking down, getting foamed, and turning to mist than conventional oils. This allows a car to be pushed harder, tow longer, and rev higher than a car with conventional oil, where the oil breaks down, no longer protects, and parts either wear out, or seize.
Also, you can run the oil longer in the engine, safely, and save the environment from nasty used oil that is changed more frequently. But then again, most Americans truly don't care about the environment, and only give lip service about it. Can't break their tried and true habits of changing the oil every 1k to 3k miles, and they never needed to rebuild and engine after 150k miles on this car, blah, blah, blah.
An additional note: In the past two trucks I've owned, which I mentioned above, I ran the recommended oils until about 15,000 miles. At that point, I switched to 15W40. At around 85,000 to 100,000 miles, I changed to 20W50. I believe it best to use a heavier oil in a high mileage motor, and I also believe that heavy oils in general are best. When I told a guy years ago that I was running 20W50 in my 93 truck I mentioned above - he told me I'd ruin the engine because the oil cap says "5W30 only" on it.
Well, it is owned by a friend. It is still running and rolled over 383,000 miles on my birthday this year. Original engine, of course.
It bugs me to put 0 weight oil in an engine, but I am doing it. Someone educate me. Please.
Personally, I would have recommended sticking with the recommended oil viscosity until you are completely out of the Power train warranty period, just to prevent any possible harassment of the dealer and manufacturer. And with todays engines, so little wear occurs after only 15k miles, switching to the heavier oil doesn't add any protection, it just makes the car harder to start when cold, and increases wear under cold starts, and taxes your car's battery more.
After you are out of the warranty period, its all on you to fix the engine, and no one really cares what you do, except for the person who has to buy the car/truck/motorcycle/lawnmower/whatever from you afterwards. Honestly, if you operate your vehicles just like everyone else on the planet, you aren't seeing any extra benefit from the heavier weight oils, because you aren't pushing the engine hard enough to get it to the levels where 5W-30 isn't thick enough to protect the engine.
Here's a quick comparison:
Mobil Clean 5000 5W-30 (conventional oil) Flash point is 392 degrees F, Pour point is -27 degrees F.
Mobil Clean 7500 5W-30 (synthetic blend) Flash point is 392 degrees F, Pour point is -44 degrees F.
Mobil 1 15W-50 (synthetic oil) Flash point is 455 degrees F, Pour point is -38 degrees F.
Mobil Delvac 15W-40 (diesel oil) Flash point is 456 degrees F, Pour point is -22 degrees F.
Mobil 1 5W-30 (synthetic oil) Flash point is 446 degrees F, Pour point is -54 degrees F.
As you can see, the Mobil 1 5W30 has the best cold weather protection in case you live in Antarctica, and really doesn't give up much high temperature protection in comparison to the two heavier oils. Typically, a normally operated car or truck engine runs between 180 and 260 degrees F for oil temps.
Of course, there are points in the engine where its going to be a lot hotter than others.
Piston rings, and cylinder walls will see the highest temperatures, since that is where combustion takes place at. The higher the temperature the oil can withstand there, the less wear will occur, and the less oil your engine will burn in the long run.
You asked for answers, and there you go.
BC.