Hydraulic oil coolers?

[Captinjack]

My backhoe hydraulic oil over heats after about an hour of operation. It has done this since new and the supplier is worthless and the manufacturer isn't much more help sooooooooooo. Is it feasible to install a small fan powered cooler on the return line so that I could keep on working?

I have a PTO driven pump that had the drain and fill/vent plugs reversed releasing all the oil from the speed increasing gearbox. The clear sight glass showing the proper oil level traps oil and ALWAYS shows the proper oil level even without any oil in the box!

I got that corrected and use Royal Purple oil in the pump drive, but it's better but not good enough yet.

The reservoir tank holds about 5 gallons and the BH is a Prairie Dog 7.5 made in Bugaria.

I only have about 20 hrs. tops on the hoe so this overheating problem needs to be fixed.

Thanks for any input y'all can provide.

 

[RonMar]

Define overheated? How are you measuring this overheat? If the return line to the resovoir is unrestricted/low pressure, then I don't see why you can't add a fan/coil oil cooler. My next question would be is since they don't come with a cooler, is adding a cooler a fix to a problem or a bandaid that will mask the actual problem? Hot oil is caused by friction, Friction is caused by pressure. Are you sure about your plumbing being correct? Could you possibly have a fitting, QC, pipe or hose that is overly restrictive or clogged? Is the flow from resovoir to pump suction clear and unrestricted? Is the pump matched to the application(too much pump, too much backpressure)? I would probably start with a pressure gauge "T"d into the pump output/valve inlet so I know exactly where I stand before heading in the direction of re-engineering the system.

If your dealer isn't a good resource, I would try going to Praire Dog directly. Does everyones overheat/is this common? Are you in a particular climate that would make it likely to overheat?

Good luck

 

[sandman2234]

I would think that just adding a cooler without a fan would be a help and probably not be near as much problems. Putting it in the air flow of your existing radiator fan would help considerably but would take a lot of extra piping. Adding more reserve might be easier than adding the cooler, by just adding an extra tank under the tractor. My Ford has a similar tank, but it is for fuel, not hydraulic oil.
David from jax

 

[Captinjack]

Define overheated?

The return line got soft and blew out spilling oil all over the place. This happened the first time I used the hoe for about 2hrs. It has gotten really hot every other time I used it. The paint started burning off the reservoir tank one time when I was digging out a stump. I don't know what the temperature was, but I know or believe it was in excess of the 180 deg. F limit.

Are you sure about your plumbing being correct?

There is only a high pressure out from the PTO pump and a low pressure clear 3/4" line for the return. The return line is clear with spiral wire to prevent collapsing. I changed the filter and that didn't make any difference.

I did contact the mfg. and they recommended to check the pressure on the system. I have a pressure gauge with the fittings and hoses that they recommended, but I've not connected it yet as I.......A. am not sure how to do this and B. I thought the PTO pump not having any lubricate in the gearbox was what was causing the high temps. This doesn't appear to be the case as it still gets too hot to work more than about an hour or so. Checking the actual pressure is first on my troubleshooting to do list. The BH is 265 miles from where I live so this isn't going to be a run out to the garage and try this experience.

Could you possibly have a fitting, QC, pipe or hose that is overly restrictive or clogged?

While the BH is not overly powerful, in my limited experience with tractors and hoes, I don't think a system designed for 2000 psi will be any more powerful than it is. The boom up function is a bit slow. There is nothing obviously clogged or causing too much back pressure. Are there any tests to determine this?

Prairie Dog says that this is not a common problem, but we all know how these statements go especially from someone we don't have any previous experience with.

Many thanks for your quick reply. I appreciate the knowledge and experience of the posters on this forum. That's why I don't post often although I am a voracious lurker.

I just did a search on google and found some fan coolers and some technical books on hydraulics. I bought a $37 book from them to educate myself as I know I can understand this stuff. I'm an electrical whiz so the hydraulics shouldn't be too difficult. I didn't appreciate the importance of delta P or pressure drop, but it makes total sense as it would be the same as a resistance in an electrical circuit.......it generates more heat the more you increase the resistanc. I've got my work cut out for me, but am confident that success will be achieved. The hoe is virtually new although I've had it for two years. I just never had to use it very much.

 

[RonMar]

There is nothing obviously clogged or causing too much back pressure. Are there any tests to determine this?

The pressure gauge "T" d into the pump pressure outlet or the valve high pressure inlet will help to determine this. That valve should be open center, so with your hands off the controls, the pressure at operting RPM should be Zero, or very, very low. In this condition the oil shouldn't be getting all that warm. Now if you ran a cylinder to it's stops and held it there for an extended ammount of time with the safety relieving, then I would expect the oil to heat up. The pressure should only rise when you are working a cylinder and then only as much as the work the cylinder is doing would create, up to the max pressure allowed by the relief. Another check is how long it takes to fully extend or retract a cylinder. If you know the cylinder diameter, stroke and rod size, along with the pump GPM output, you can calculate how long it should take to fully extend or retract the cylinder under no load and compare that to how long it actually takes.

A restricted suction line between tank and pump could cause pump cavitation and overly heated oil.

I don't think I have ever seen a clear hydraulic line, return or otherwise. what you describe sounds like something from Home Depo's plumbing department. It is a return line so it dosn't need to really be pressure rated, but what you describe dosn't sound very temperature resistant.

 

[john_bud]

If the paint is burning and the hoses exploding (ok, I'm being melodramatic!), you have a serious issue.

With a cold tractor, start the BH hydraulics and run them without operating the BH at all for 3 min. Stop and feel every hose for heat and the pump & controls. There shouldn't be any heat. Repeat 3 times. If you feel heat in one location, that's the spot to focus on (or the upstream spot!). If the pump is gettting hot, take the hoses off the pump and look for junk in them and in the pump.

I would check that the pressure relief valve isn't cracked open. When cold, start the machine and feel / listen by the pressure relief valve (screw in deal next to the inlet to the BH controls). You may hear fluid flow or heat. Take it out and look for small pieces of junk.



If the boom lifts slow, the cylinder could be bypassing the packing. Raise the dipper stick all the way and take the boom up and down as fast and far as you can 10times. Shut off the engine and feel the cylinder to see if it is getting hot. It shouldn't be even warm. Do the same with the dipperstick and then the bucket curl cylinder.

I suspect that you have a major restriction somewhere. Maybe an internal bypass in the pump or a cylinder. I doubt the relief, but it is the first thing to check and the easiest to clean/ correct. Given your comment on slow boom lift, I suspect it.

jb

 

[Soundguy]

I agree with ronmar.. I'd check for restrictions ont he flow and bad plumbing.

Oil making a relief valve open will REALLY heat the oil.

Also, too narrow of lines.. or a line inadvertantly assembled with a flow restrictor can cause problems. Also to high a volume of pump for that hoe / plumbing will restrict the oil flow.. etc.

I'd go with a oil cooler without the fan on the low pressure side if i added one. .. also.. if no filter inthe system.. add one.. a big one too..I wouldn't rule out a gallon sized one if i could find an application /xref/ filter that fit a base that wasn't way expensive... it dissapates heat on it's surface area too, and adds oil volume... all of which will help you.. etc..

Soundguy

Define overheated? How are you measuring this overheat? If the return line to the resovoir is unrestricted/low pressure, then I don't see why you can't add a fan/coil oil cooler. My next question would be is since they don't come with a cooler, is adding a cooler a fix to a problem or a bandaid that will mask the actual problem? Hot oil is caused by friction, Friction is caused by pressure. Are you sure about your plumbing being correct? Could you possibly have a fitting, QC, pipe or hose that is overly restrictive or clogged? Is the flow from resovoir to pump suction clear and unrestricted? Is the pump matched to the application(too much pump, too much backpressure)? I would probably start with a pressure gauge "T"d into the pump output/valve inlet so I know exactly where I stand before heading in the direction of re-engineering the system.

If your dealer isn't a good resource, I would try going to Praire Dog directly. Does everyones overheat/is this common? Are you in a particular climate that would make it likely to overheat?

Good luck

 

[sandman2234]

Were you having problems with the overheating before that first line broke? I realize it was in the lower hours of the machine, but just wondering.
I took my Steiner's suction hose down to the hydraulic shop and they made me another. As standard practice, I retain all old hoses and mark them in case I need another in a hurry. When I picked up the new hose, it was the same size on the O.D, but was 1/8" smaller on the I.D. I almost missed that, and requested the right hose. They couldn't make it, so I went with the smaller one, but it seems to be noticable in function. Due to room, a larger one necked down wasn't an option.
I just wonder if that happened to you?
David from jax

 

[Captinjack]

Yeah. The oil got hot right out the gate. Being a newbie, I didn't know what to expect from anything regarding power temps etc.

After about an hour of digging a ditch in relatively soft dirt, the return hose just "melted" close to the tank end. I was able to quickly reconnect the hose by sliding it over the male spiquot and prevented the wholesale loss of fluid.

I waited till the next day and the same thing happened again regarding the overheating , however this time I was watching how hot the fluid got and stopped before the hose got too pliable.

I still haven't been able to make any further checks yet as the tractor is at my deer camp. Unless I find something very obviously causing the overheating, I will install a cooler, but that may not be till spring 08.

 

[Soundguy]

That's not correct or good.

High temps like that will degrade components in your hyd system.

sounds like something is running against relief greatly heatingthe oil.. or you have a huge mismatch in flow rate capability to capacity.

If you don't find out the problem soon.. it will become apparrent as things stop working from melted seals or lots of metal showing up int he oil as parts self destruct..!!!

Did I mention that this was serious and you need to find the problem??

I don't think this is a 'lack of cooler' issue. vs a real 'problem'.. etc..

Soundguy