Oil Change questions

[Ag NSX]

What's the difference between 5w-30 and 10w-30 oil? I know its a weight difference, but doesn't the 30 designate its viscosity range? Isn't the 5w-30 good for winter because its lower viscosity is good when its cold. What would happen if you ran a car with 5w-30 in the summer as opposed to 10w-30? Would the oil be thinner?

Also, what do you guys do with the used oil? Where do you dump it?

 

[Lud]

The two numbers designate the viscocity at different temperatures. The first number is the viscocity when cold. The second is the "effective viscocity rating" at operating temperature.

These are not absolutes, they are relative to temperature. That is to say, with 10W-30 the oil is not 3 times thicker at operating temperature, it is simply a light 10 weight oil when cold that stays at thick as a 50 weight oil would at operating temperature.

The reason you do not want to use 5W-30 when it's warm outside is that the oil is too thin at cold startup to provide good protection. The reason you DO want to use it when it's extremely cold is because the 10 weight oil will get TOO thick to provide proper lubrication during a cold start.

You shouldn't "dump" used oil ANYWHERE! Call around to local garages and auto parts stores and see who will take your used oil for no charge. I think most of the major chains will these days.

[This message has been edited by Lud (edited 17 April 2001).]

 

[Ag NSX]

Thanks Lud, the part where I'm confused is when you say, 'The reason you do not want to use 5W-30 when it's warm outside is that the oil is too thin at cold startup to provide good protection.' But isn't operating temperature hotter than start-up temp? So how can it be a 5W at start-up and then 30W at op. temp?

 

[Lud]

It is somewhat confusing. Read the 2nd paragraph again. They are not absolute values.

At operating temperature it is as thick as a 30 weight oil would be AT THAT TEMPERATURE. It is not as thick as 30 weight oil if you were just pouring it out of a bottle at room temperature.

 

[Ag NSX]

So if I drive my NSX in winter, should I use 5w-30 for an oil change in Oct. or just use 10w-30 all the time? Of course, in Chicago, we go from 70 degrees on Sat. to 35 degrees on Wed.

 

[nel]

An informative and interesting reading regarding engine oil can be found at:
http://www.geocities.com/chrislonghurst/engineoil_bible.html

-Nick

 

[Lud]

I would not use 5w-30 unless more often than not it was well below freezing when I started the car. I believe the owners manual recommends when to use which.

Actually, if it well below freezing often when I was starting my car, I'd get a heated garage or an engine block heater but that's a different topic!

 

[David]

You really don't need to go to 5w-30 unless it is really, cold - like below zero F or -20c.