Whats the difference between 10w40 and 5w30?

Question

I've been using 10w40 for my rig(v10 6.8L) The owners manuel recommend 5w30. I have 105k miles am I putting my huge ol rig at jepordy with this radical change of oil?

Answer 1

here is a definition of the numbers. use 5w30 as the example. 5 is the viscosity of the oil when cold. the lower the number, the thinner it is. W actually stands for winterized (but most just refer to it as "weight"). the 30 is the viscosity when hot. the oils are considered multi-weight since they change viscosity at different temperatures. now to answer your question, the oil you are using is fine. the more miles on your motor, the more worn out the parts in the engine will be (especially crankshaft bearings and journals). this will cause gaps to be slightly wider than when you first bought the car. using a thicker oil will actually be better for a very worn engine :)

Answer 2

The numbers refer to viscosity (pourability or thickness). These are multi-viscosity oils. The first number refers to the viscosity when cold. The second number refers to viscosity at operating temperature. So, theoretically the oil starts out thin when it needs to spread throughout the motor from the oil tank, then reaches a thicker viscosity once the engine warms.

You should always use the recommended oil. Using 10w40 means you're using an oil that starts out too thick (10 instead of 5) and ends up even thicker (40 instead of 30) when it warms up. The costs are equal. Use the correct oil if at all possible.

Answer 3

Most of us have only a vague understanding of viscosity. We tend to choose an oil with a viscosity that we believe is correct for our particular engine, but would another viscosity improve or reduce the life of the engine? Can we freely pick and choose a viscosity outside a manufacturer's recommendations?

Technically, viscosity is defined as resistance to flow. Commonly though, we

Copied from:
http://www.blackstone-labs.com/oil_viscosity.html

Answer 4

Viscosity mostly. It basically shows you what the oil does from cold to hot, when cold, it acts like 10 and hot it acts like 40 weight for the first, 5 and 30 for the second. No, no problems that you used slightly over the recommended weight.

http://faq.f650.com/FAQs/OILFAQ.htm#Oil%20Viscosity will give you more if you want to go deeper into the question.

Answer 5

10w40 is thicker (lower viscosity) oil than 5w30. It's lubricating properties are different, especially in higher than or lower than normal operating temperature ranges. You should follow mfg. recommendations. I don't hink you have done serious damage yet.

Answer 6

One reason the manufacture uses a lower W (weight) grade oil is to improve there CAFE rating. The thinner the oil the less resistance to the engine operation, consequently, better millage.
That's one reason synthetic has become so popular.

Answer 7

If you've been using 10w40 all along, it is doubtfull anything is wrong...the difference is actually that 5w30 is slightly thinner than 10w40...really, your engine probably runs just fine with what you have been putting in it always...