Bondioli & Pavesi

[marrt]

I called B&P and had an interesting discussion with one of their engineers. Here's a few highlights for the knowledge base:

+ My older, new generation 425 has the 21cc M4PV21 pump, not the NT10 pump. The NT10 is now discontinued.

+ He strongly recommended the use of hydraulic fluid (46AW or 68AW) over motor oil. Hydraulic fluid has a much better additive package for wear, rust inhibitors and dealing with water and ail infiltration. According to him, "the fluid is the most important thing on the machine." He said some of the newer synthetic fluids, effectively, had the same multi-viscosity characteristics as motor oil. This is necessary for avoiding cavitation during cold starts.

+ He did NOT like the use of a suction side filter due to cavitation potential during colds starts. He suggested running the RPM's as low as possible until the fluid warms up or consider using a magnetic heater on the tank.

+ And finally, he suggested adding a 3 micron filter on a return line somewhere, or building a filter cart. The 10 micron filter will not provide optimal cleanliness for the pump.

+ He said both the NT10 and M4PV21 have relief valves built into the pump itself.

Very nice guy.

 

[ponytug]

Dear Marrt,

Thanks for the update. It is great to have input from the manufacturer.

Personally, your post will add some impetus for me putting in a fine filter somewhere. I'm think of the return beyond the joystick. Some of the older 14XX have a fine filter (on the high pressure side of the steering/FEL circuit I think).

I looked into the motor oil vs hydraulic fluid, and what I came away with was that if you run at one temperature, hydraulic fluid is probably the best choice for all of the reasons cited. If you have cold starts, motor oil is the way to go. There is a huge difference in viscosity at low temperature, which may be why the B&P engineer dislikes pre-filters, which do induce cavitation much more strongly in hydraulic fluid.
10W40 has a viscosity of 14.6 @212F vs 839 at 32F
30W oil has a viscosity of 10.5 @212 vs 1257 @32F mm2/s kinematic viscosity.

Everyone claims additive packages, but what is in any given oil is known only to a couple of people at the plant, which makes it tough to compare. There are a few motor oil sites that have oil parameters over time for something of a bake off between motor oils. I have never found one for hydraulic fluids.

I split the difference and went with synthetic motor oil (better shear resistance, and supposedly better additive packages) 10W50 (better high temperature viscosity, and probably not worth it.).

Thanks again for the information.

All the best,

Peter

 

[marrt]

Dear Marrt,

I looked into the motor oil vs hydraulic fluid, and what I came away with was that if you run at one temperature, hydraulic fluid is probably the best choice for all of the reasons cited. If you have cold starts, motor oil is the way to go. There is a huge difference in viscosity at low temperature, which may be why the B&P engineer dislikes pre-filters, which do induce cavitation much more strongly in hydraulic fluid.
10W40 has a viscosity of 14.6 @212F vs 839 at 32F
30W oil has a viscosity of 10.5 @212 vs 1257 @32F mm2/s kinematic viscosity.

Peter,

I thought the same...until I discovered this site: SAE Multigrade Oil Properties

The viscosity of 10W40 motor oil is 94 cSt at 40C and 14.6 at 100C (as you note)
The viscosity of 68AW is 68 cSt at 40C and 8.7 at 100C

The means 10W40 motor oil is about 50% thicker at start up. This is bad because, in cold climates, it could create cavitation.

Further, the optimal viscosity for my MP4PV21 pump is 15 cSt +/- 35 cSt. This means I'm FAR below the optional for a cold start. The 10W40 has a viscosity of 881 cSt at 32F. No wonder the pump whine's so much. BTW, here's a cool calculator for this stuff: Jiskoot - uid and gas hydrocarbon sampling

Assuming the running temperature of the hydraulic oil is about 180F (does this sound about right?), the 68AW would deliver a viscosity of 13.8 cSt vs. 22.54 cSt for 10W40. Both are within the optimal range in this condition. However, the 10W40 is on the high side, which would generate significantly more heat and, I assume, "waste" more power.

What about a system with wear? Wouldn't the thicker oil work better? It's an interesting question. Common sense says yes, but my gut says no. I think the thicker oil would end up reaching a higher running temperature, which would raise the viscosity and negate the benefit. That's my theory at least.

 

[woodlandfarms]

My 1850 has a 25 micron high pressure filter on the steering lift tilt dump circuit. Shcroeder N-25

When does cold start really come in to play? Generally we get down to about 45 at night with around 10 nights at 28 a year. Tractor is clunky but gets going.

 

[MossRoad]

I've managed to start mine (25hop Kohler gas engine) with no pre-heating and only using a shot of starting fluid at -5F. It was not pretty. And it gets harder to do that as the tractor gets older each year.

 

[ponytug]

Hmm...I compared UTF and hydraulic oils, but I haven't ever checked 68AW. Thanks for bringing it up.

When you get to pumps and filters, you start to get into a viscosity regime that is no longer macroscopic. Some oil folks talk about "shear", but the concept is highly relevant to high mileage engines or pumps with lots of hours or grit on them. The gaps between the rotors or vanes and the walls of the pump or motor get larger due to the wear and more oil slips through the gap. High viscosity generally retards that, but there are significant non-linear effects to this "microscopic" viscosity. It is related to how attracted the lubricant is to metal, and how well the oil entangles other oils. I tend to think of the effect as microscopic tumbleweeds.

To get a feel for the effect, you can try stirring a thick suspension of cornstarch- you can stir it slowly, but if you suddenly move your spoon, it will lock up.

I think it is great that you have optimal numbers for your pump! I'm not a cavitation expert, but I suspect being 50% high isn't a huge issue, but I also suspect that doing as many do here of letting the tractor oil come up to operating temperature before using it is a great idea. Makes me think that a plug in oil heater might be a great idea for my tractor.

All the best,

Peter

 

[SpringHollow]

For many of us, the question is what is the viscosity at low temps like 0°C (or much lower in my case), not at 40° C.

Ken

 

[marrt]

Ponytug,

I agree with your points. And, to be clear, while 68AW may be a good comprise if one has frequent cold starts, this doesn't mean it's the best compromise overall. My goal was to figure out the best hydraulic oil to use, since I want the benefits of an additive package specifically designed for hydraulic systems. Viscosity is only one consideration. Here's a chart giving the recommended viscosity for various pump designs:

http://media.noria.com/sites/magazine_images/201007/pg28.gif

And here's a chart showing the tradeoff between mechanical efficiency (i.e., difficulty to pump thicker oil) and volumetric efficiency (i.e., less bypass in a worn system).

http://www.designnews.com/photo/157...olumetric_efficiency_curve_increasing_the.jpg

If you can maintain your tractor in a climate controlled condition, then you may want a viscosity on the high side of "optimal." The chart below suggests an average optimal range of 10 cSt to 50 cSt for the "average" pump. In that circumstance, 10W40 motor oil would be a good choice. Using a synthetic motor oil, I doubt you'd have a problem even down to 0F. At 0F, the viscosity of 10W40 is 3843 cSt. That's still below the cavitation limit in this chart.

http://media.noria.com/sites/archive_images/Backup_200507_LubSelect-Fig2-Viscosity.gif

As usually, the more I read, the more confused I get.

 

[ponytug]

When it comes to oil selection, I'm right there with you...
All the best,
Peter

As usually, the more I read, the more confused I get.

 

[J_J]

Has anyone converted to hyd fluid, and if you did, did you see any difference?

I also have a Case 1845c that uses motor oil for the hydraulics, but they also add a qt of special additives.

PT has been using 10W-30 or 40 since the early 90's. Have not heard of any problems

I am not buying the fact that hyd fluid is better.

Here in Florida, I could probably get away with 30wt non detergent, so any water that got in the system would settle on the bottom.