These numbers are used for both synthetic and dino oil. They describe a modern multi-viscosity oil as it compares to old-style single-weight oil (like the 30W you put in a lawn mower).

Keep in mind that the lower the number the thinner the oil. 90W gear oil (used in transmissions and differentials) at room temperature is like cold maple syrup. Light machine oil, like you might use on a sewing machine, is I think like 5W.

Also keep in mind that the colder an oil gets the thicker it is, thus it gives more resistance to moving in the engine (but it protects against wear better). The hotter oil gets the thinner it is, and the more likely it is to be completely squeezed out from between two moving metal parts, thus providing no protection (this is called "shear").

OK, given this, in a multi-viscosity oil the first number is how well it flows when cold and the second number is how well it protects when hot. Thus, a 10w-40 flows like a 10W when cold and protects like a 40W when hot. That's why the lower the first number and the higher the second number, the more "high-performance" an oil is considered to be.

I was amazed and delighted when I first saw a 5w-50 oil because I knew it would not give my engine any resistance to flow at low temperatures, but it would strongly resist shear when I was pushing a hot engine hard.

How's that, guys? Pretty good explanation?

 

thanks for the explanation! how's the royal purple workin for ya? i heard it is a pretty good motor oil and helps with power gains too

 

I just recently heard from a Red Line re-seller that Mobil 1 is not a true synthetic. Can anyone confirm or deny that claim?

I've used Mobil 1 for 15+ years and was obviously shocked at hearing that statement.

 

I've been happy with the RP motor oil, but then motor oil is very much a leap of faith anyway. I haven't changed out the first RP fill; that will be soon. Hint: shipping for 3 cases of RP was the same as shipping for 1 case. Go in with your friends if you can.

I'm convinced that you get a little boost in HP and mileage when you change from dino to synth, just because synth is inherently slipperier than dino, so you have reduced friction.

I used Castrol dino on my 93 Accord (bought new) and Castrol Syntec on my 98 V6 Accord (bought new) and the difference in how those two car's engines performed and aged over 5 years sold me forever on synth. From that decision, you just have to find the best synth for the money.

IMHO (and based on what I have read) there are "tiers" of synth; Castrol Syntec & Mobil 1 are on the lower tier, rumours abound that they are not "true" synth (whatever that means; I remember a stink a couple of years ago when Mobil announced that they were reformulating Mobil 1 and the general consensus was that they had cheapened the product and were no longer "true synth"). The next tier up includes Amsoil, Royal Purple, Redline, and several others I can't think of right now.

I read the RP web site in depth, critically reviewing some of the studies they published that were conducted by NC State University, a respected engineering school that happens to be in my home town of Raleigh, NC. The studies seemed to be conclusive that RP was at least as good and probably better than most oils, including some tier 2 synths (like Amsoil). I then discovered that I could get RP for about the same price, maybe a little more, than Castrol Syntec. My mind was made up and I have used RP ever since.

FWIW

 

Like I said before, "Royal Purple is the ****!"


bhobson333: Have you tried running any of there other fluids like there tranny fluid or rear diff? If you haven't a strongly advise you to try it. You will be amazed at the results I know I was.

Just .02 from another Royal Purple user for life!

-David