Change from a thick to a thin mineral oil
If you are eg running Mobil 1 brand 15W-40 and change it to Multi-grade mineral oil, 5W-20 your gas mileage will probably go down 30%!
What happens is that your oil flows faster and for that reason never get hot enough to require a thicker 40 grade oil.
The lower temperatures you will see with the thinner oil occurred because of reduced friction and internal drag and higher oil flow and better cooling.
So, since the 20 grade oil is thinner it got better flow and therefore better cooling and lower temperature.
The 20 grade oil is at a lower temperature because it was not as thin than it would have been at the previous higher temperature with the 40 grade oil.
Cooler engines also last longer.
Fact: The higher the temperature, the greater the wear, all other things being equal.
OBS! The 5W-20 does not thicken as much after you turn off your engine and this is the very important point.
90% of the tear and wear is caused by the few seconds you start your engine and you don't need to be in a winter climate to benefit of the W-oils.
With the right oil at operating temperature (212F/100C) there is very little wear and tear, most of the wear and tear occurs when you start your engine.
Because of these facts, all manufacturers are now specifying 0W-XX or 5W-XX oils.
Honda, Ferrari, Ford, Mercedes, Porsche, and others specify a 0 or 5W-XX oil to mention a few.
These are appropriate for all engines of all ages of all levels of wear.
This second number is the only thing that may change with an older, lose or worn engine.
The oil grade you need can only be determined by experimentation. If you are using XW-50, go to a 0W-40. If your pressures are still too high go to a 0W-30 and so on.
Remember you also have to wait for the oil to warm up.
Water / coolant warms up on just a few minutes but oils takes up to 30 minutes to get up to just the normal operating temperature of around 200°F.
Older engines may also in fact benefit from thinner oil use. Over time permanent deposits of carbon and sludge build up in the engine oil ways.
It is like a clogging of arteries in humans. We are now all on blood thinners.
The synthetic oil of the same viscosity as the mineral oil will be an improvement.
An even thinner synthetic may be better off.
To get away of the clogging you could just use a thin synthetic oil and change it every 200 miles for a while and end up with an even cleaner engine.
Remember, the only difference between a 0W-40 and a 10W-40 is that the 0W-40 thickens less after you turn off your engine.
It is still too thick in the morning at startup but not as thick as the 10W-40.
Yet, they are still too thick to use until they both warm up to operating temperature at which point they have the save viscosity, around 13 to 14.
Remember that the 0W-30, 10W-30 and straight 30 grade oils all have a viscosity of around 10 at normal engine operating temperatures.
They all thicken when you turn off your engine. The 10W-30 will thicken the most.
The 0W-20 is the best choice because it will thicken least.
There is one more thing. A 20 grade oil is not half as thick as a 40 grade oil.
The real scale is more like the oils having an absolute thickness of 108 and 114.
Now it can be seen that the 40 grade oil is only around 10 percent thicker than the 20 grade oil.
The difference is not that much at operation, but at startup the difference is significant.
Pressure / flow dynamics go along with this 10 percent figure.
A 30 grade oil should be thought of as having an absolute viscosity of 110 and a 50 grade oil has an absolute viscosity of 120 at operating temperatures.
Everyone knew that 90 percent of engine wear occurs during the startup period because oil is just too thick, that's way you want to have a 0W oil with as low grade as your engine can take at the operating temperature.
Make the test and check oil pressure and temperature. Oil temperature is normally about 5% higher than the engine temperature.
For a modern Turbo Disel engine using SAE 30 grade oil the operating temperature is between 78C to 80C at 2500 RPM and the Oil pressure is about 42 psi.
OBS! Over time, the car manufacturer have been specifying thinner and thinner O ils.
tect the same or better?
I gues my main concern/question is about the VI index(improvers) added. 10w 30's have less than 5w 30 oils, and the higher the VI index(5w 30) the better it is for bearings, and being pumped throughout the OHC engine right? Shouldnt that make 5w 30 way better than 10w 30?
