Go BottomHuh Motor Oil instead of Hydraulic oil
 | WillieH
Join Date: Feb 2003 Posts: 543 New England 
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2006-09-05 134000
Ok ~
I have heard of alot of different things before, however, this one stumps me so I figured I would throw this out on the table for discussion / insight.
Came across some documentation for a Great Bend 751 backhoe. Two items popped up that caught my attention. The first, was there is NO hydraulic oil in this unit, rather 10W40 motor oil (?).
I was always led to believe, that the whole idea behind hydraulic circuits was that of the heat capabilities and expansion factors of hydraulic fluids offering excellent coefficients, versus standard oils (motor oils) offering few to none. Yet this model 751 backhoe from GreatBend (maybe additional models as well), requires 10W40 motor oil (?).
Secondly, it goes into detail for securing threaded pipe fittings. It identifies, that "Never use teflon tape to secure a seal...." Rather "use only a teflon paste".
I have heard that power steering fluid works in some hydraulic circuits, quite well. However, PS fluid IS a hydraulic oil.
I am curious ~ Any insight would be appreciated.
- Willie H
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 | beagle
Join Date: Jan 2004 Posts: 1333 Michigan 
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2006-09-06 134004
The teflon tape comment is standard for hydraulic circuits. You should not use tape in high pressure circuits because the threads of the joint cut the tape as the joint is tightened. This can leave slivers of tape inside the joint that can end up in the circuit and cause problems. It's always best to stay away from tape in hydraulic circuits.
The motor oil is a little more curious. I assume the unit you are looking at has an independant pto hydraulic pump, and does not run off the tractor hydraulics. Not only is the viscosity quite a bit different for motor oils, hydraulic fluids (brake/power steering/automatic transmission, etc.) are formulated for high flow applications. Even 10w40 oil would seem too heavy for an efficient hydraulic application, causing excessive heat build up at the pump.
....
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 | kthompson
Join Date: Oct 2005 Posts: 5275 South Carolina 
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2006-09-06 134007
I believe you will find the biggest problem with the teflon tape is it getting placed to low on the male fitting, past the threads. That sure would allow the tape if cut to move into the system. If used properly it sure would seem hard for that to happen. Of course when a fitting it removed, the female part should be cleaned.
At same time, would not a glob of paste creat some problem?
Long years ago we had to use teflon tape on stainless threads as the paste would push out of some fittings. The paste could be better now or the threading of the stainless could be smoother. That was 20 years ago.
kt ....
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2006-09-06 134010
First off, the reference to teflon tape is more likely the result of someone using it wrong and getting pieces of it clogging up the machine which the manufacturer then fixed under warranty before they realized it was a defective component, just a defective operator. LOL.
As for the hyd. oil, yes this is common, especially in light hyd. and HST circuits, all our commercial mowers for instance call for motor oil ONLY as hyd. fluid.
The weight of the oil is not as bad as you would think, our JCB backhoe for instance runs straight 68 weight hyd. oil in it's hyd. system.
Best of luck. ....
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2006-09-06 134013
Some systems with the motor oil do require an additive to work properly. Most all hydraulic oils are of a 30 weight and less in the ag tractor line with some of your better hydro oils into the 10 weight range. We've had to watch what we recommend for about 15 years now for hyraulic ol in some skid steers as well as other equipment. ....
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 | DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2006-09-06 134017
My dump trailer uses ATF. ....
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 | kwschumm
Join Date: Feb 2003 Posts: 5764 NW Oregon
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2006-09-06 134018
My Bandit chipper uses 30 weight motor oil in the hydraulics. So does our log splitter. ....
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2006-09-06 134019
My problem with multigrade oils is the fact the surfactant in the oil can absorb water if the system is allowed to stand for a long time. This is why a lot of lawn mowers recommend straight weight oils.
Like other oil discussions on the board the newer oil's surfactants maybe a lot better at suspending dirt without attracting water.
The biggest difference between ATF and hydraulic oil is the level of surfactants. We often use ATF to clean and free up an old engine due to its high level of surfactants. ....
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| WillieH
Join Date: Feb 2003 Posts: 543 New England
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2006-09-06 134020
The 751 in question, does in fact have a pto pump set up rather than tractor hydraulics, so needless to say, there had better not be any contamination from one circuit to the other.
My dump trailer uses ATF as well, however ATF is still not -"motor" oil persay.
Kind of interesting - I had no idea that so many equipment pieces currently on the market, used motor oil in the hydraulic circuits.
Question: By using a motor oil in place of a true hydraulic oil, would it require a different setting of the pressure control/relief valve for proper operation? Or, is there a general operating pressure for motor oil versus hydraulic oil in the same system? (speaking of compact backhoes here only)
Thanks to all -
I always say, a day that one does not learn something new, is a bad day!
~ Willie H ....
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 | earthwrks
Join Date: Dec 2003 Posts: 3853 Home Office in Flat Rock, Michigan
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2006-09-06 134035
My New Holland skid steer uses 10W-30 for the hydraulic system and the final-drive chain cases.
Engine uses 15W-40.
When I quizzed my dealer on the 10W usage he said it was to reduce foaming at high temps., and reduce internal corrosion of the hydraulic system. ....
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 | greg_g
Join Date: Jan 2004 Posts: 1816 Western Kentucky
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2006-09-06 134037
Murf, the "68" in AW68/ISO68 is not the same as engine oil "weight". ISO68 hydraulic fluid actually has a SAE viscosity equivalent lower than that of 30W engine oil. There's a reasonably straightforward viscosity chart at http://www.bobistheoilguy.com/visc.html
//greg// ....
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