I got water in the hydraulic fluid of a Bobcat 720 so was changing out the fluid by running it out the accessory hose. Unfortunately, I ran the pump dry. I don't know hydraulics, but the concepts *seem* easy enough. Famous last words, eh? I hoped that topping up the reservoir and radiator might get the fluid where it needs to be. It didn't. I replaced the filter, filling the new one before screwing it on. I tried filling through the openings on the top of the pump. I figure I need to crack open some/all of the output lines from the pump, but... I don't know the routing! I'm not sure which are "in" and which are "out." I've tried to figure out which Vickers pump is in there and look for a web resource that can tell me which is which. No dice. The only numbers I see on the pump (which has several thick coats of paint to try seeing through) are the patent number and a six-digit which does not come close to the model numbers. I figure it is a serial number. Any suggestions?
Bobcat 720 lost hydraulic fluid prime
- Thread starter dmccr
- Start date
Great advice. I am not confident there is oil in the pump, as I can't get it to flow. The reservoir is below the pump level, so I doubt opening the valve to the aux coupler will work. Gravity is not on my side (in more ways than one). That is why I was trying to fill the radiator... to use gravity. It is mounted above the pump.
The only other way is to put a jack under the back to stop it tipping back. Use another jack or chain hoist and lift the bucket/arms up in the air while someone sits in the seat to operate the lift pedal. This will draw oil through the pump and into the lift arms as they extend, it essentialls prims the pump. I have done this when re-installing a pump, it worked for me, hopefully it will for you too.
The other way is to operate the aux hydraulics and use a vacuum cleaner, and draw the oil through. You just need to get a little oil moving to get to the pump.
Fancy! Now to figure out how to drag this beast down to the barn where I can hook up the chain hoist!
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Even if you remove the pins holding the end of the ram to the arm, lift the arms and block them high enough to pull the end of the ram stick, as long as you can extend the ram sticks, it will draw oil through the pump.
You guys rock! I'm primed! Now the dilemma is how to get all that milky fluid out of there! Think a helpful eight-year-old with an empty milk jug and a kitchen sink. Lots of water in that "radiator." I've already put 15 gallons through the machine.
The only way i know short of pulling every hydro line is to run the machine, that includes lift tilt and drive then dump the fluid, repeat till the oil is clean. Remember to change or at least drain the hydro filter. I did this on a machine, drained the filter a few times during the oil purge, worked pretty well. You may need to re-prime like you did before after every cycle you do.
I've had a couple of suggestions to speed the process... Seafoam Transtune additive and Mercon (instead of regular oil). I don't think I want to get the dye in there... I'll never get it out! The Seafoam is tempting, as it says it removes water. How it "removes" it is really the question... bonds to it and causes it to evaporate? Bonds to it and keeps it in suspension?
It will hold it in suspension, it will hol don to it, not make it disapear. The best way may be to run it, then dump the oil a few more times to get the water/seafoam mixture out.
I personally would run cheap and nasty oil through it to flush, then use the correct grade you want to run the last two changes.
Just remember to operate ALL functions between changes. Drive it, lift/tilt, make it work, get the oil flowing around. This way you will replace all the old oil with fresher oil, then you drop it then it happens again untill its as clean as it can be.
There was another member that bought some cheap water absorbing filters, then ran his oil through the quick couplers to get it as dry as possible. I don't know how much they cost, and how much they could absorb. When your oil is white, it has to go, you can't just suck up the water. It wouldn't be a bad idea for when you have done a few changes to get it to a good colour though, but this is your call.
Mikethomas
New member
- Joined
- Oct 25, 2025
- Messages
- 1
Does 10/30 only work or does hydrostatic work?
The only difference between engine, hydraulic and hydrostatic oils are the additives. The base oil is all the same.
On older machines a good hydraulic oil is normally used these days as new engine oil additives, like detergents, can harm seals.
You just need to get the correct weight oil for your climate or season that the machine gets used in. In mild climates a good AW46, in cooler climates a good AW32 and so on.
I live in Oregon and my climate is pretty mild so I used NAPA AW46 in my Bobcat 742. Never had any problems and the price won’t break the bank.
Sapientoni
Well-known member
- Joined
- Jun 13, 2025
- Messages
- 103
It can get confusing if you go to Tractor Supply to get "hydraulic" oil. The key guide these days is the AW42 or AW32 designation by your machine manufacturer. Just like engine oils used to be just 10w 30w 40w etc. and now they are specified such as WSS-M2C963-A1 , or DW FE SS SE etc
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