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Old 08-03-2008, 07:39 PM   #1 (permalink)
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Synthetic steering fluid for better FE?

I am wondering if it would be worth the expense to change the standard power steering fluid with synthetic to improve FE.

The only place that I can see that it should help is in reducing friction in the vane type steering pump. Pressures would still be the same of course so energy would not be saved there.

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Old 08-04-2008, 01:10 AM   #2 (permalink)
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Sounds like you just want an excuse to spend money on synthetics.

No real improvements in FE to be had here.
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Old 08-04-2008, 03:23 AM   #3 (permalink)
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The pump really doesn't do much until you steer. The fluid does circulate but just in an open loop and there really is no load until there is steering input.

Synthetic or not there wouldn't be a noticeable improvement if any at all.
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Old 08-04-2008, 07:01 AM   #4 (permalink)
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Quote:
Originally Posted by ConnClark View Post
Sounds like you just want an excuse to spend money on synthetics.
Not quite! Synthetic ATF is over $9 a quart where I shop.
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Old 08-04-2008, 12:34 PM   #5 (permalink)
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the pump is always running and pumping all the time, just in a closed loop, so a smoother fluid should have less friction, and if the rest of the steering system is working smoothly then the power steering pump should work less when you do ask it to work, just like when I drive other peoples early 90's civic and notice that their car steers hard because their tires are poorly inflated, they never adjust the gear slop in the rack and pinion, or lube any of the rest of the pivot points.
as long as that power steering pump is turning it is doing at least a small amount of work and the less friction you have the easier it will turn and the less gas you will use, so I say do a compleat steering tuneup if you do anything.
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Old 08-04-2008, 01:20 PM   #6 (permalink)
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By changing synthetic steering fluid, it may save some gas, but you don't see the difference. Pray for good traffic helps even more.
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Old 08-04-2008, 01:41 PM   #7 (permalink)
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...as long as that power steering pump is turning it is doing at least a small amount of work and the less friction you have the easier it will turn and the less gas you will use..
Yes, this is why I was contemplating changing to synthetic. The question is, how MUCH less gas will you use, i.e. how long till you realize a payback?

As you mentioned, even when the pump is not developing power to steer the wheels it is still continuously pumping. It seems that it would be beneficial if that fluid were multi viscosity since pumping it continuously in cold weather is going to waste even more gas. Or better yet, maybe improvise a way to use the engine heat to heat the steering fluid in the winter.
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Old 08-04-2008, 02:34 PM   #8 (permalink)
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I just figured out how to measure how much energy the pump is using, when NOT actually supplying energy to steer the wheels.

With a cold vehicle measure the temp of the pump. then start the engine and run it at say 2000 RPM for 5 minutes. Now again measure the temperature of the pump. It should be warmer. The amount warmer is the amount of energy it is wasting. Now you need to weigh the pump to get a total mass of metal, and separately weight the fluid that is in the pump (not in the rest of the system).

The metal of the pump can probably be reasonably correctly assumed to have a specific heat value of 0.12 (that of steel). This means it will take 0.12 BTUs to raise the temperature of 1 pound of it 1 degree F. If the pump weighed 10 pounds and if its temperature rose 5 degrees F in 5 minutes (if, if, if...), that would mean 1.2 BTUs were generated in 5 minutes. That is a rate of 72 BTU/hour. That equals 0.028297063 horsepower.

The above did not take into account the specific heat of the PS fluid in the pump but it would be similarly measurable and then just add it to the above. The fluid in the pump would be a rather small contributor to the whole considering the specific heat of oil is much lower than steel and the total weight of the fluid is much less I am sure.

So, about 3% of a HP if the above "ifs" are correct. In other words, to be 100% of a HP (1 HP) it would have to raise the temp 33 times as high, or do it 33 times as quickly or the pump would have to weigh 33 times as much OR any combination of the above.

To do this test correctly, any potential for heat gain and loss, other than that being generated in the pump, would have to be isolated. You would have to put insulation around the entire pump for the duration of the test with a temp probe affixed to the pump.

Please feel free to correct my math as I am doing this a bit hurriedly on my lunch break.
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Old 08-04-2008, 03:17 PM   #9 (permalink)
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I think the use of synthetic helps the service life of parts more than the power its freeing up. That being said, the most neglected power steering pumps either outlast the car or they quit for "no reason," something defective inside eventually fails. I throw syn in my manual transmissions, and syns in my engine oil, because they thrash and heat up much more than any PS system. I think at 9 bucks a quart id just change with cheap stuff. With three quarts the money saved can almost fill up my car. 300 miles.
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Old 08-04-2008, 04:07 PM   #10 (permalink)
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Quote:
Originally Posted by getnpsi View Post
I think the use of synthetic helps the service life of parts more than the power its freeing up...
But isn't the reason that it helps service life due to reduced friction?

They say to NOT use syn motor oil in a new motor until the rings have seated. The reason given is that the syn motor oil is so slick the rings will not seat if it is used from the start.

Reduced friction means longer service life, less heat generated and thus less energy required at the input.

I recently changed my manual transmission oil to synthetic and the first thing I noticed is that it shifts much nicer, presumably due to less friction. The dino oil that I drained out was quite new too. It only had 5k miles or so on it.

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