breathment

Alright, i'v always been confused when it comes to the
(x)W-30 on oil.. I know it has to do with the ability of the oil to flow when cold. but thats about the most detailed explination i'v heard.. Can someone go through the w's and give me a more detailed explination?? Don't our cars or at least 88 350's require 5w-30?? Thanks

five7kid

iTrader: (14)

Ah, the mysteries of "multi-viscosity", "all-season" motor oils...

The number preceding the "W" is indeed the cold temperature viscosity. The measurement is called "kinematic viscosity", and the unit is called a "centistoke". The actual number on the can is a "rating", not the actual centistoke value. The ratings and ranges are controlled by SAE.

A lot of games have been played with these ratings. The reason GM wants a 5W oil to be used is that 5W and below oils have to have a pour point below -20 degrees F. 10W and higher oils do not, they just have to fall within the viscosity range for that rating. The reason for that is that during the winter of '83-84, the Big Three bought a bunch of engines under warranty when the midwest went through a cold snap of -20 F days for about a week. The cold oil turned to jello and wouldn't pump. People started and took off in their cars anyway, and lunched a bunch of bearings.

FWIW, a GM rep was heard to say that they didn't have to warranty a single engine for that reason that winter that had synthetic in the crankcase.

breathment

so in the summer time. wouldn't it be best to run a straight 30 weight?? also since it never gets below 20* in texas, and im runnng mobil 1 syn. anyways.. which is better as far as performance, which flows better? or does it not really matter as long as it is (*)w-30??

five7kid

iTrader: (14)

Synthetics "tend" to be more naturally multi-viscosity, meaning they meet both the cold and hot viscosity ranges. A lot of them still add viscosity index improvers, though.

Oils that meet the "W" as well as the hot requirements tend to pump a little easier when the engine is first started. But, again, synthetics "tend" to do a better job of cold start-up protection, so using a synthetic would be better than using a multi-rated petroleum.

Synthetics also "tend" to have better hot temperature protection, another reason to use them rather than a straight-weight petroleum.

I've put all these "tend" caveats in because there is a wide variety of quality amoung the synthetics. The majors only have them so they can say they have a synthetic, and what they put on the shelf is junk (Mobil the one exception). I'm biased towards AMSOIL (but only because it's the best), but Red Line makes good stuff, too. Don't know enough about Royal Purple yet, except they're doing more advertising and sponsoring.

Grim Reaper

There are other reasons for using a "thinner" oil (i.e. 5W30 vs 10W30). 1) Thinner oil "shoots" to the bearings and begin lubricating quicker than thicker oil at "startup". 2) The thinner oil has less "internal resistance" hence you get a "little extra power" and "little better gas mileage".

Over my 30+ years of driving, I have used a variety of oils in a variety of engines. My current car (91 GTA) has been using 5W30 Mobil 1 since I bought the car new in 1991. After 200,000 miles, I STILL don't burn any oil. I have a little oil that "leaks" in the intake manifold, but I still leak less than a quart every 3,000 miles.

And yes, my car is actually faster and gets better gas mileage than when I first bought it...but that is primarily due to burning my own eprom.

89WS-6

So, right now, I am using 10W30 Castrol GTX synthetic. First off, is ths a good oil, or should I go to mobil. And second, what would change if I went to 5W30 Mobil oil. By your reading, it wouldn't operate as well cold, but would be better when it warmed up. Right? Please set me straight. I've always just used 10W30 because it is factory recommended. But knew about this conspiracy so to speak. Set me straight! Thanks,

breathment

so the lower the W, the better it flows at cold temps?? but has a little more friction then a higher w. or is it the other way around? with the exception of synthetics..

Vader

Instead of my customary novel on mineral oil properties, you can search the archives. Besides, 5-7 already covered the bases quite well, and in far fewer words.

Typically, mineral oils that are multigrades are made from base stocks that have a true viscosity of the lower, or "W" number. That means that 5W-30 mineral oil is really SAE 5 oil that has viscosity improvers (polymers) that make it act like SAE 30 oil at higher temperatures - to a point. These polymers are the first thing to burn away in a mineral oil, causing ash, sludge, and oil breakdown. Once those polymers start to burn away, you're running with nothing but 5W oil in the crankcase on those 105° degree days.

Synthetics (true synthetics) are more stable across a much larger temerature range, and therefore don't require viscosity improvement polymers to maintain adequate viscosity at higher temperatures. No ash, no sludge, no breakdown. And that is in addition to the many other benfits.

If you read your owners' manual, there is a section on engine lubrication. There is a temperature scale in that graphic that shows SAE 30 as an acceptable lubricant above 40°F temperatures. Actually, it is the preferred lubricant, but will cost you a little more in fuel until it gets warmed up fully. And you need to warm up the engine well before loading it, which you should do anyway. Even my 2000 van has the range, with SAE 30 specified above 40°F. I ignored that part of the manual and immediately went to synthetic after driving it home, so I don't sweat it. Then again, I'm lazy and like things to be easy.

As a sidelight, I use Mobil mostly because of the availability. I was a bit concerned that they were falling behind the technology and "cheaping out" a little when Mobil merged with Exxon, but some recent imporovements in the formula have reassured me that it is a completely acceptable lubricant. Oddly enough, the Mobil 1 5W30 and 10W30 have cold pour and pumping points that are within 4°F. 5W pours at something like -76°F, while 10W30 will only pour at -72°F. (I forget the actual numbers, if those aren't correct - but they're close.) The pumping points are within 3°. And the coldest I've ever started a vehicle was -44°F. The battery made so little voltage that it had to be charged to crank, but I had oil pressure as soon as I let go of the key. Even the snowmobiles wouldn't start by hand cranking. (Those northern Wisconsin mornings can get a little brisk, especially after Glenn sends some air that way.)

After some research, it is apparent that Amsoil is a premium product. If they would work on their marketing a bit, they'd really have soemthing there. I haven't been able to find a lot of technical data on Red Line or Royal purple, but have seen info on Castrol, Penzzoil/Quaker State (same company), and Valvoline. It appears that those are not true fully synthetic base stocks, and are simply synthetically modified mineral oil bases (they're not using synthesized molecules). They are probably just fine for engine lubrication in most cases - just not in mine. Even the lawnmower and snowblower get Mobil 1. I told you that I'm lazy...

Vader

And for reference:

https://www.thirdgen.org/techbb2/sho...threadid=25058


https://www.thirdgen.org/techbb2/sho...threadid=29469

1987fbd

So Vader/57, what would you suggest doing with an engine that has 160,000 miles on it. I have no idea what oils he has been using but it has the famous cloud of smoke at the start. It runs very strong with lots of power still so i am holding off the overhaul for a while longer. My question, is it going to smoke more at startup going with a synthetic based oil? And also don't these have a cleaning action to them? With that in mind I am sure I have alot of buildup after 160,000 miles and would hate for the synthetic to knock a bunch of that loose and cause problems. So what should I do, go synthetic or stay with the cheap stuff like Castrol?
Thanks guys this has also been a mystery for me!!
:hail:

ede

i like amsoil better than mobil but it's easy to pick up a quart or two of mobil 1 every time i'm at wal mart than it is to buy amsoil. personally and for no good reason i wouldn't run castorl ,i like pennzoil for dino oil. i know everyone has their own ideas about oil and what works and what doesn't. actually i think the cheap stuff from wal mart, prep boys, or anyplace else is great if you keep it changed like you should (3000 miles), but how many really do?

breathment

thanks