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Use same viscosity with synthetic?


exbass94

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Kind of a stupid question, but since I'm a newb once again I think this is a good opportunity to ask one. If I switch to synthetic, should I still use 5w30 as recommended by Ford? Will I develop any timing chain noise? I have 14k miles on the SOHC and ZERO noise, and I would like to keep it that way. I would probably use the Napa (Valvoline) synthetic. I also need it to perform well in both 100 degree (Fahrenheit) weather, and around freezing (32* F) temps.
 


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Yes. Viscosity is viscosity, at least for crankcase oils (the index is different for gear oils).
 

exbass94

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Yea, that's what I figured, just wanted to make sure. Thanks a lot.
 

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Yes. Viscosity is viscosity, at least for crankcase oils (the index is different for gear oils).
Micheal, let me pick your brain and ask a noob question. I know I should know the answer to this but I tried to explain it the other day and couldn't.

break down the multi- grade for me...... I know the lower the first number the better the oil flows. and I know it used to be the older an engine got the higher the second number needed to be........ but at what point do you start using 10w30 as opposed to 5w30. what point do you start using 10w40 as opposed to 10x30.... My Suburban has 207,xxx miles on it and it seems to have better oil pressure with 20w50 than it did with 10w40, same with my Jetta with the bad oil pump. I know diesels use 15w40 because bigger gaps and clearances.... I know precision engines need 5w30 or even 0w30 (synthetic) because of tighter gaps and almost non-existent clearances. But at what point do you switch weights on the oil?
 

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The 10W and 30 are both "viscosity indices." The "W" is measured at 0 deg C, and the other at 100 deg C. In other words, cold weather starts, vs. normal operating temperature. Unfortunately, they aren't the same indices (10W at 0 deg C is not the same viscosity as 10 at 100 deg C). But SAE has specs on both, for crankcase oils and gear oils.

You use 5W-30 if you live in an outrageously cold climate and you don't have a block heater or garage. You use 10W-30 otherwise. Even in winter in most of the Lower 48. 10W-30 and 5W-30 behave the same at operating temperature.
 

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ok that makes more sense than the way it was explained to me years ago..... so why would you use 10-40 on a more worn out engine and why does my engine knock go away with 20-50.......... I had an old ford that I ran straight 30 and another we used 90w gear oil in it.
 

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Oil is a pretty good octane smasher. A little leakage down a valve guide or two and it will rattle like a 6 foot diamondback. Viscosity can affect leakage rates. It can also take up excess clearance, but it VERY OFTEN does more harm than good. Generally, you don't have all your clearances widened by just the right amount, so something gets underoiled.

90W gear oil isn't all that much more viscous than 20W crankcase oil (but it has a wildly wrong additive package).


Straight weights are appropriate for vehicles that never get very cold. Straight "W" weights might appropriate for vehicles that never warm up....at least in really cold temperatures.

IMO, you DON'T run heavier weights in old engines. If the oil pressure is really that bad, it needs a rebuild (or a valve job or a gasket) and you're just going to push it over the edge. Underoiling risks catastrophic damage such as thrown rods. But most likely, it will just hog out all the clearances and make the oil pressure that much worse.

The most important thing is to use the oil the vehicle was designed for. Your old Ford may predate multigrades...

FYI, I have always used factory spec oil in all my vehicles. The only one that has suffered an engine failure was the former Bronco II (2.9L), which made it to 250K miles before it hosed a camshaft. The current owner reported the crank and rod bearings looked "bright, shiny, and new."
 

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A little leakage down a valve guide or two and it will rattle like a 6 foot diamondback. Viscosity can affect leakage rates. It can also take up excess clearance, but it VERY OFTEN does more harm than good. Generally, you don't have all your clearances widened by just the right amount, so something gets underoiled.
With synthetic, use the same viscosity the manual recommends. That said, like MAKG said earlier, you can run 10w-30 instead of 5w-30 in warmer months or if you live someplace warm all year. Thinner oils are to help mpg and CAFE results, BUT modern engines are designed for them so it doesn't hurt anything.
My wife's car calls for 5w-20 which you'd think would be pretty thin, in fact oil changes go quickly because it pours out like water, but I've sent a few samples to an oil lab for analysis and they were fine.
High mileage engines can sound quieter and burn less oil with a heavier weight, but that's only because it's thicker and isn't getting past the wider clearances. That doesn't mean it's good for your engine though since you may run into the "underoiling" problem.
 

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