I have never figured out why we have oil weights. The 10-30W, 20-50W, 30W, 50W, etc. just don't make sense to me. Well I guess it's never been explained to me. So can someone explain the reason for different weights and the uses of the 10-30 20-50 and the straight 30 or 50 weights, and so on. Or if you know of a web site I could check out that would help too, Thanks! ahknodd

 

its based on how oil flows at certain operating temperatures and environments. if your car is manufactured to have certain pressure tolerances at certain operating environments, you have to consider the lubricant you will use when you design the motor. oil and pressure and how it flows is dependent on temperature mostly, all atmospheric inputs depend on pressure and how a substance will expand, etc. oil has to be at operating temperature to operate and protect fully, hence the do not beat your car until its warmed up mentality. your oil actually isnt protecting your motor until its hot. different weight oils flow differently and have different heating/cooling characteristics that can be defined as its viscosity. how it protects under load, etc. there is an optimal operating environment for each oil however not always an optimal oil for a motor. honda maintains that 5-30w or 10-30w oil is what they reccomend. due to VTEC addiction and hotter temperatures here in FLA I run a 10-40 synthetic based on the suggestion of the oil manufacturer and after collecting information from techs I know. My car has been running well. A suggestion: know WHY you are running a certain oil program and dont change it too many times. your engine likes to be ran consistently for long bearing life. the lower number means its viscosity when it is cold, and the high number is its viscosity while hot. not all oils are created equal however and I will steer clear of rehashing that post