Quote:
Originally Posted by PANAVIA
3. Dean - SAE 50W >? wow!
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Quote:
Originally Posted by thudmaster
Dean, run what you like...........it seems to work for you.  |
I don't wish to steal any thunder from the topic in question (which has been largely resolved at this point). But the whole
oil selection has raised a couple eyebrows
, so here is the rationale behind it.
Thicker
oil is really misunderstood since it's really referred to as more viscous
oil. Viscosity is the measure of SHEAR resistance, the very thing you don't want to happen inside an internal combustion engine. Viscosity is NOT measured as to how thick it is. The two just appear to be connected in most cases. But, too many people think only of the oil when it's COLD... never after heating it up.
More viscous oil when hot is pretty thin. Put some 50w in a pan and heat it up to 230 degrees and tell me if you want anything THINNER lubricating your motor? Thinner oil does not "get into tight places" anymore than more viscous oil. PRESSURE takes care of that. Aha!
Less viscous oil will break down and thin out more when hot. And, yes, even Synthetics will when compared to a more viscous oil.
More viscous oil cools more not because it's thicker...that would make it HOTTER right? No, it's not that, it's because it sticks to metal more and it therefore transfers more heat.
Heat up some WD-40 in a pan to 230 degrees and roll it around. It foams, smolders and vaporizes. Now try some 10w-30... it does the same at about 260 degrees. Straight 50 is pretty stable through a similar test.
Now, some will say "270 degrees?!? My engine doesn't get that hot!" If you have 230 in the pan, it will be WAY hotter at the bearings and pistons just before that... and 270-300 is about average before it gets back into the pan. Bearings melt at 375 degrees... which is about 270-300 in the pan.
But remember, you MUST adjust the clearances in the engine to allow the more viscous oil to FLOW. What I have been taught is that thinner oil is for really tight engines with little flow. And not having enough oil flowing past the bearings is what makes them hot. THAT's why racing engines have bigger clearances... not to reduce friction, but to allow the use of the better MORE VISCOUS oil to "flow" past parts. Pressure, clearance and viscosity are all connected... and changing any one will affect the other.
And remember, many times the low oil pressure you see at the gauge with more viscous oil and cooler temps is NOT the restriction of the oil getting into the engine. It's the restriction of the oil getting into that teeny little dead ended oil tube going to your gauge :-)
Last ad. I live in generally warmer So Cal (it's not Phoenix or South Florida). But we tend to have more normal temps and not radically cold weather where starting up a car with 50wt would be a death sentence to most motors.
The defense rests, your honor.
-Dean
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