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Can someone explain what oil "weight" is? Like 10 w 40. Does that mean when it is cold it is 10 weight but when it heats up it is 40 weight? Or vice versa. Is it better to use a heavy or light weight oil. I currently use 10 W40 all year round. Should I use something else, like straight 30?

Thank you.

Stang6767
Bryan
 

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The "weight" of an oil is a measure of it's viscosity. A multi vis oil, like a 10W-40W, will operate at the lower weight when cold and will gradually become more viscous as the engine warms up. A single weight oil is less effective since it will not provide as much lubrication when cold and will probably break down more readily when hot. I use 10W-40W in my 302 with 97K original miles because I wanted the greater viscosity after I installed the 3.55 gears. Prior to that I used 10W-30W. If you live in a very harsh climate (real cold or real hot) then you should adjust your oil accordingly. Something thinner in the winter and something thicker in the summer.

Hope this helps,
RagTop
 

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Oil Weight refers primarily to the viscosity. The higher weight numbers, the higher the viscosity and density of the oil. Straight weight oils (without the W) are intended for 9 month operation. The oils with a W such as 10W-30 are designed for year round operation. The lower the first number, the lower the temperature you can crank and pump at a specified rate. In the summer I always use 10W-40. In the winters I will sometimes use 10W-30.
(OK, I cheated. I looked this up in one of my engineering handbooks. And you thought I was smart!)

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Now 293 ci (.030" bore) with Holley 450 and 295,000 miles
MCA #49294
 

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Also the W in a 10W-30 indicates it is good for winter driving. The lower the first number followed by the W indicates the oil is good for lower outside temps.


Dave
Reading PA
66 Signal Flare Red Vert
302 2V, 15X7 Cragar SS's with 205/60s
 
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