Can viscosity make this big of a difference?

TallPaul · Aug 14, 2004

Had a practical experience in viscosity today. Bought a hand pump (looks like a grease gun can) to do the power steering changes instead of the tedious turkey baster method.

Well first time I used the new pump I had just been on a 20 mile run so the fluid was hot and likely a viscosity in the neighborhood of 8 cSt. Pump pulled a pint out in no time, but was hot to hold.

Next time I tried it, it was cold, about 60 F. So I will guess that the steering fluid was about 80 to 120 cSt. Guess what? Didn't want to come out. Was using a 3/16 inch ID tube about 2 feet long (both times). Pulled the pump handle out and it was very hard to pull. Let go and it would spring back an inch. Finally did get the pint out, but it was a real chore. Had to hold it with force and wait for the fluid to sloooowly come into the pump. Wasn't pinching the tube down inside the steering pump either as I tried it again in the waste ATF bottle and got the same result.

I just figured that it would have pulled out about the same. Wow! Imagine the stresses on your oil pump at cold startup?

rpn453 · Aug 14, 2004

quote:

Originally posted by TallPaul:
I just figured that it would have pulled out about the same. Wow! Imagine the stresses on your oil pump at cold startup?

Is oil pressure that much higher when it's cold? I've never had a pressure gauge on my vehicles.

XS650 · Aug 14, 2004

quote:

Originally posted by TallPaul:

I just figured that it would have pulled out about the same. Wow! Imagine the stresses on your oil pump at cold startup?

You did an interesting experiment, accidentaly.

The problem isn't stress in the pump as much as it is the fact that the pump cavitates when the fluid is to viscous to get sucked up. When the pump cavitaes, no fluid gets sucked in so none gets pumped out

That's the reason for the importance of the pumpability test in the xxW part of oil viscosity tests.

427Z06 · Aug 14, 2004

quote:

Originally posted by TallPaul:
Had a practical experience in viscosity today. Bought a hand pump (looks like a grease gun can) to do the power steering changes instead of the tedious turkey baster method.

Well first time I used the new pump I had just been on a 20 mile run so the fluid was hot and likely a viscosity in the neighborhood of 8 cSt. Pump pulled a pint out in no time, but was hot to hold.

Next time I tried it, it was cold, about 60 F. So I will guess that the steering fluid was about 80 to 120 cSt. Guess what? Didn't want to come out. Was using a 3/16 inch ID tube about 2 feet long (both times). Pulled the pump handle out and it was very hard to pull. Let go and it would spring back an inch. Finally did get the pint out, but it was a real chore. Had to hold it with force and wait for the fluid to sloooowly come into the pump. Wasn't pinching the tube down inside the steering pump either as I tried it again in the waste ATF bottle and got the same result.

I just figured that it would have pulled out about the same. Wow! Imagine the stresses on your oil pump at cold startup?

Oh baby, is this a real stretch of extrapolation.

HolesInTheHead · Aug 14, 2004

quote:

Originally posted by TallPaul:
...Pulled the pump handle out and it was very hard to pull. Let go and it would spring back an inch. Finally did get the pint out, but it was a real chore. Had to hold it with force and wait for the fluid to sloooowly come into the pump. Wasn't pinching the tube down inside the steering pump either as I tried it again in the waste ATF bottle and got the same result.

I just figured that it would have pulled out about the same. Wow! Imagine the stresses on your oil pump at cold startup?

Oil pump would be pushing the oil. Isn't it easier to push a fluid than pull it?

mechtech · Aug 14, 2004

There is a pressure relief valve in the PS pump, so I wouldn't be concerned at all.
I've used gear lube in those hand pumps, and it's hard to believe that ATF won't pump at room temperature. Must be an internal valve or hose collapsing.

TallPaul · Aug 14, 2004

quote:

Originally posted by mechtech:
There is a pressure relief valve in the PS pump, so I wouldn't be concerned at all.
I've used gear lube in those hand pumps, and it's hard to believe that ATF won't pump at room temperature. Must be an internal valve or hose collapsing.

It does seem excessive. To confirm the hand pump isn't clogging, I will have to try a side by side test today on both hot and cold fluid.

tpi · Aug 14, 2004

quote:

Originally posted by Gary Allan:

I think XS650 struck on it a little. You've got an air gap in the hose and are basically relying on a vac/pressure differential to move the fluid into the pump. When you push it out ...it's a little more direct.

You're counting on atmospheric pressure which is 14.7 PSI (sea level).

The oil is pushed up to the oil pump intake from the pan by atmospheric pressure.

Look at the relative size of intake and exhaust valves, intakes nearly always larger.

This is why turbocharging or supercharging is effective in increasing HP. You're no longer counting on atmospheric pressure to fill the cylinders, the air is being pumped in.

JohnBrowning · Aug 15, 2004

TallPall, Geritol!!! B-12 injections might help as well! I use my suction gun for cold gearlube.

TallPaul · Aug 15, 2004

I tried it again. It actually was not quite as easy with the hot (right after 20 mile drive) and not quite as difficult with the cold fluid (70 F this time), but still a big difference. Also, pushing the fluid out the pump did not seem any easier as I clearly remember struggling to get the cold stuff back out. Also, made a big mess in the corner of the garage with the stupid curled plastic tube flipping around when it got out of the jug a couple times.

The thing is, I am running a smaller tube than the suction pump came with. I wrapped a few turns of electrical tape around it and wedged it into the end of the larger tube. Without the step down, it pumps much easier, but the smaller tube was needed to get down deep into the steering pump. I was getting 16 oz each time.

TallPaul · Aug 15, 2004

quote:

Originally posted by JohnBrowning:
TallPall, Geritol!!! B-12 injections might help as well! I use my suction gun for cold gearlube.

What can I say.

Must be gettin old.

Gary Allan · Aug 15, 2004

Paul

I can't speak with intelligent authority (as in explaining it) but you've got two different modes of "moving fluid". I imagine that it was easier to push the heavier fluid out of the pump gun than it was to "suck" it into it.

I think XS650 struck on it a little. You've got an air gap in the hose and are basically relying on a vac/pressure differential to move the fluid into the pump. When you push it out ...it's a little more direct.

Maybe someone with a little more applied physics can state it better ..but even with JUST WATER ..vacuum can only establish a water column of so many inches ...regardless of how much vacuum is applied.

That is, although vacuum can be expressed in "negitive poundage" (so to speak) it doesn't act the same way on veritical flow of liquids.

Anybody got a better grip on what I'm struggling to say here??

[ August 15, 2004, 01:23 PM: Message edited by: Gary Allan ]

Can viscosity make this big of a difference?

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