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If the reservoir is full of oil and the loader cylinders won't move, then most likely, the pump is toast.

What you have is called an "open center" hydraulic system. Oil is gravity fed to the inlet of the hydraulic pump and then pushed by the pump to the loader control valve. From there it returns to the reservior to be pumped again. The only time the pump does any serious work is when one of the two levers is pushed or pulled. The flow of oil is then diverted to one end of the cylinder/s or the other.

In order to test your system for the max pressure it will put out, you need a glycerin-filled pressure gauge capable of reading at least 3000 PSI. You also need some hydraulic fittings and a high pressure hydraulic hose to connect the guage to your system. You need a Tee fitting that will you to insert it right at the point where the high pressure hose coming from the pump to the loader valve screws on to the loader valve. Remove that high pressure hose from the loader valve and screw on end of the Tee fitting onto the valve and then screw the hose onto the other end of the Tee fitting. The third opening on the Tee fitting connects to the high-pressure guage.

In order to test for pressure, start the tractor after installing the above items and checking that you tightened all fittings. With the tractor running at half throttle, pull the bucket control lever backward and hold it in that position. If you don't see the pressure increase on the guage, to at least 500 pounds, then the pump is likely weak and needs to be replaced.
 

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Tudor makes a good point about the relief valve. It should be located in the loader control valve. Photos would be a huge help here.

The guage is a twenty dollar item here http://tinyurl.com/ku8l8m and can be found for as little as twelve at some places.

Item 4020 is overkill for your tractor but it will certainly work. http://tinyurl.com/nt8kuv

If you click on any one of the three valves shown at the top of this page http://tinyurl.com/nvv2mx and then enlarge the photo, you can see the relief valve on the end closest to you and the adjustment/access to the relief next to the control handles. The relief consists of a concave seat with a steel ball bearing sitting over the hole drilled in that concave seat. There is a coil spring that presses the ball bearing against this seat to close the hole off. If the oil pressure in the system rises higher than the pressure from the spring, then the ball will lift off the seat and allow the oil to escape back to the reservoir.

If a piece of junk gets stuck between the ball and the seat, then the hole will remain open. If the spring breaks and then collapses into itself, then the ball won't stop the flow. Rule out the relief valve first.

It it's ok, then remove the pump and take it to a hydraulics shop. They can run the number and tell you if parts are available. Belt driven pumps use special bearings to support the side loading that a pump that is coupled straight on to a shaft never encounters. In other words, any new pump you contemplate buying, must have bearings capable of handling the side loading stresses from belt drive.
 

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Doug,
When testing hydraulic systems to see what pressure is there, you can't take any chances on have a guage that won't handle the pressure.

Realistically, your Bolens with a hydrostatic drive will have what's called a "charge pump" that is part and parcel with the whole hydro unit. That charge pump serves a purpose for the hydro but it can also be tapped into to provide some modest hydraulic power for cylinders.

At best, your pump would put out perhaps 3 or 4 GPM and be able to develop 1000 PSI tops. I suggest that you go to the Bolens site here at MTF and provide that list with the model and serial number of your tractor. They can probably tell you which make and model hydro is in your unit and then the specs can often be found on the manufacturer's website.

In other words, you need to know what SHOULD be there in the way of pressure in order to make a test. Remember this..... max pressure in a hydraulic system is created when a cylinder has travelled as far as it will go and you still hold the lever in the ON position. Go buy a gauge that reads 3000 PSI and it will cover almost all the tractors you are likely to own. Systems in the 4000 PSI range are not very common compared to systems that max out at 2200 PSI.
 

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I think you've found the problem BUT....if the pump has been starved of oil for a long time, then essentially.... it has been allowed to run in an almost "dry" state and that does not bode well for any pump. I would take the tank and screen to a place that has a heated tank filled with caustic soda and ask them to cook it for you. Engine rebuilders have such tanks as do automotive machine shops that specialize in doing valve jobs.

I would also carefully dismantle the pump. Do this on a clean bench and spread a large rag on the bench to catch anything that might fall from the pump when you open it up. Look for accumulations of metal filings and heavy scoring in the end plates. Check the gears for any sign of metal galling.

If you are unsure about what you see, then take the dismantled pump to a local hydraulics shop for a 1 minute inspection. Their experienced eyes will know just how good or bad this pump is. Depending upon what you find, you might want to remove all of the hydraulic lines and wash them out with solvent. The rod end of the loader cylinders should be removed from loader so you can pull the rod/piston in and out to remove all of the old oil.

This is your opportunity to really clean this hydraulic system up. If you are really, really lucky.... the pump will still have some good life in it but that life can be shortened if you leave contaminated oil in the system to circulate. As for oil, you can use ATF or any universal hydraulic fluid. My choice would be the ATF along with installing a true oil filter on the return line to properly clean the oil instead of just catching the rocks.
 
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