5w-20 motor oil

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I just bought a new car last month. My previous car was a 1997 model and it specified 10w-40 motor oil, as had every car I have owned for the past 30 years. This new car (a 2005 Ford Focus) specifies 5w-20 oil. I've since found out that 5w-20 has been pretty much standard for the past couple of years.
Question: Why the apparent reduction in lubricating requirements? I can understand that theoretically the 5w requires less power to pump and therefor *might* result in some mileage improvement; but the high temp reduction from 40 equivalent to 20 equivalent doesn't make sense to me.
What am I missing?
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Viscosity and lubricating quality are not necessarily related. I can't recall having a car since the 70's that called for 10w-40. That was a big V-8 that did not have the tolerances in the newest engines. All others were 10w-30
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A lot of the engines made today have tight tolerances, therefore needing the lighter weight 30. My 2003 Odyssey uses 5W-20 as well.
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Vic Dura wrote:

That is not a reduction in the lubricating requirements. It is an indication of a less thick oil. Less thick does not convert to less lubrication.

You are right about the reduced pumping force, but that applies to the hot measure (large number) as well. It also means the engine has to use less energy to move pistons and other engine parts all of which mean a little higher mileage.
It does not stop there. Today's engines are not designed like older engines. The parts are made with closer tolerances so the heavier oil would not lube or cool (cooling is a function of oil as well) them as well.
Stick with what the manufacturer recommends. If you want better oil, try synthetic. Of course be sure to use nothing by synthetic if the manufacturer calls for it.
The lubrication and other specifications are part of that letter after the "S" You can use any oil rated equal to the "S" number specified or higher. ("C" number for diesel engines).
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Vic Dura wrote:

Others answered the basic questions, I'll just note that for years long ago, Chevy specified 20-20W in all their truck engines--I've still got one '58 which has been through every harvest since it was new and has yet to have any work whatsoever other than normal maintenance. <Still> using 20-20W in it... :)
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There is also a subtle consideration or the local ambient temperature range. Where I am, from now to October we can ecpect day highs about 90 or better and night lows in the 70's. I have been running 10W-30 in my 92 Explorer for 174k+ miles with no problems.
Charlie

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What you're missing is that bulk viscosity has little to no relationship to the lubricating performance in thin films at high contact pressures, and that the spacings and tolerances are in the bearing are differant/smaller in the newer engines so a lower visc is required/desired. The lower viscosity oils do cause lower pumping losses and narrower visc ranges e.g. 5W-20 vs 5W-30 or 10W-30 vs 10W-40 or 10W-50 require less viscosity modifier additives (which tend to break down over time). So in short, use what is recommended, though it may seem odd at first.

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On Sun, 19 Jun 2005 06:13:59 -0500, Vic Dura

your not missing much... From the other posts use the recommended oil..
I have a 2001 Saturn that likes to drink oil.. It has 91000 miles on it.. Bought it new.. uses 1quart every 1000 miles.. Your milage will very...
The oil change schedule I've followed religously from the day i bought it new (w/130 miles)..
130-500 Change (5w30) every 2500 til 50000 (5w-30) every 2000 til engine dies..(10w-40) Summer, (5w-30) Winter
The 10w-40 has stopped the oil usage by 1/2 quart however still burns it :(...
also check the oil for when it turns black the filter is full and needs replaced.. (At least my saturn does it on the mile @ 2000)..
I've Penzoil from the 1st oil change and OEM Filters..
....
I've *heard* the focuses minmick the saturn in oil usage.
hope this helps
Joe
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Years ago, that was normal consumption. I have two Buicks with the 3.8 liter. The older one has 142,000 and uses a quart in 3500 miles, the newer one has 96,000 and does not use a full quart between changes at 7500 miles. Yes, that is 7500 miles between changes as recommended by GM.
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On Mon, 20 Jun 2005 07:39:34 GMT, in alt.home.repair RE: Re: 5w-20 motor oil snipped-for-privacy@a.com wrote:

Thanks for all the comments. I was never considering using anything other than the recommended oil, I was just curious about why the change. I didn't know about modern engines being built to closer tolerances. The lower viscosity spec now makes sense to me.
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Why does the change in oil specification indicate to you that there is a reduction in lubricating requirements?
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On Mon, 20 Jun 2005 12:51:48 GMT, in alt.home.repair RE: Re: 5w-20 motor oil snipped-for-privacy@fellspt.charm.net (Lawrence Wasserman) wrote:

I always thought that the second number e.g. the 20 in 5w-20 indicated the high temperature lubricating ability of the oil. So for 5w-20 the oil flows/lubricates like 5w oil when cold and like 20w oil when hot. Then going from 10w-40 to 5w-20 would mean that when hot the engine oil flows/lubricates like 20w oil instead of 40w oil.
Is that correct or am I miss-understanding all of this?
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Flows like and lubricates like are different things. The lower the number, the lower the viscosity. This has nothing to do with the ability to lubricate anything. That is determined by the composition of the oil
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Vic Dura wrote:

...
Except that it's only the (approximate) viscosity being indicated, not the lubrication properties. That's specified by the SAE letter designation (SE, SF, etc.).
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On Mon, 20 Jun 2005 15:25:08 -0500, in alt.home.repair RE: Re: 5w-20

Ok, thanks for the comments. I think I have a better understanding of it now.
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<...snipped...>

The numbers are a measure of viscosity. The engine manufacturers specify the oil viscosity according to the needs of the particular engine, based on bearing clearances, temperature conditions, testing, and many other factors. If a higher viscosity was always better we could run 90-140w gear oil in our engines.
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wrote:

The viscosity measurements are made at 0C (32F) and 100C (212F).
So for 5W20, at 0C the viscosity is the same as straight weight 5 at that temperature.
At 100C the viscosity is that same as straight weight 20 at 100C.
Still while warming up the 5W20 still thins. It has higher viscosity when cold than when hot.
I suggest a synthetic because it does not have Viscosity Improvers.
There are some good sites about oil around the web:
http://www.chris-longhurst.com/carbibles/engineoil_bible.html
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On Tue, 21 Jun 2005 22:41:37 GMT, in alt.home.repair RE: Re: 5w-20

Thanks. I'll dial-in and check them latter.
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For one thing, the numbers mean very little. Crude approximations at best. IOW, 10W30 is never as low viscosity as "straight 10" nor as high-viscosity as "straight 30" per API specs. Conventional mineral oils slip past this "kludge" and don't do what you'd hope for at high temps.
Synthetics, OTOH, typically have very little viscosity variation from below freezing to many hundreds of deg. F. They _were_ developed for jet engines, with huge temperature variations. Bottom line: just on the basis of lubricating-film-strength, a 5W20 synthetic will flow at temps below 0 F (where conventional 10W30 is like butter) and likely better protect engine innards than 10W40 when you're towing across the Mojave.
But wait ... synthetics typically reduce viscous drag at ring/bore interface enough to notably increase fuel mileage. Extreme detergency is yet another plus. Higher price, but much lower net cost. IMHO.
HTH, J
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Vic Dura wrote:

thinner the oil, better the gas mileage, I believe
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