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Old 12-30-2018, 08:00 PM   #1
Mini-Skoolie
 
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1996 cat 3116 hydraulic fan motor.

I am having a major leak in the vicinity of my power steering reservoir, hydraulic fan motor, and the hoses coming off the bottom of the reservoir. I verified everything is tight and am fairly certain it is not the hoses. I am also fairly certain the fan is not kicking on when it should/ at all. When I park at operating temp of 190 the fan should be running full blast? Iíve only ever seen the fan slowly spinning.

I had a mechanic look at it and heís trying to tell me the hydraulic motor is not working properly causing fluid to backup in the reservoir and overflow??? This doesnít sound right to me.


My theory, thereís a leak at the hydraulic motor, causing it to not have proper pressure to spin, and when it does spin on the highway just from air movement around it, itís flinging oil everywhere?


I lost about a gallon of oil in a 1.5 hour period on the highway, and stopped the first time I discovered the leak because trans temp was slowly rising. And engine was running warmer than normal.
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Old 12-30-2018, 09:11 PM   #2
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Join Date: Jun 2016
Location: Orange County, CA
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Year: 1990
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Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
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Originally Posted by DMCGARIGAL View Post
I am having a major leak in the vicinity of my power steering reservoir, hydraulic fan motor, and the hoses coming off the bottom of the reservoir. I verified everything is tight and am fairly certain it is not the hoses. I am also fairly certain the fan is not kicking on when it should/ at all. When I park at operating temp of 190 the fan should be running full blast? I’ve only ever seen the fan slowly spinning.

I had a mechanic look at it and he’s trying to tell me the hydraulic motor is not working properly causing fluid to backup in the reservoir and overflow??? This doesn’t sound right to me.


My theory, there’s a leak at the hydraulic motor, causing it to not have proper pressure to spin, and when it does spin on the highway just from air movement around it, it’s flinging oil everywhere?


I lost about a gallon of oil in a 1.5 hour period on the highway, and stopped the first time I discovered the leak because trans temp was slowly rising. And engine was running warmer than normal.
Any leak at the reservoir itself should be easy to see and easy to fix - the only connections there are low-pressure return hoses from the motor and power steering, and the supply hose back to the pump itself which is under slight suction. Or is the fluid coming out the reservoir's breather on top? If the inlet sides of the pump or motor are leaking, even slightly, you'll know about it in a hurry! 1500 PSI hydraulic fluid will spray everywhere, and I mean everywhere, from even the tiniest hose pinhole or loose connection. It's safe to assume that your pump and motor do have slight internal leakage, but that should not manifest itself as external leaks because usually the fluid is seeping past the lobes inside, not passing through the external seals. Does your motor have an internal or an external drain system? An old, tired and slightly internally-leaking motor will spin by hand more freely than a new tight leak-free motor - how does it feel when you spin the fan backwards by hand? If you disconnect both hoses from the motor or pump, either should have significant resistance to turning by hand if they are in good condition, but if either can be freely turned by hand then they are probably worn internally. Another thing to check, and something that will reveal if there's mechanical wear within the entire system, is a fluid analysis - iron or aluminum particles in the fluid will prove wear. Is the fluid black, or does it still look like new? Also, is the solenoid directional-control valve leaking?

On my bus the fan runs at half-speed (i.e. with the directional-control valve open and diverting half the flow straight back to the reservoir) up to 195 degrees, then the valve closes and runs the fan at full speed when hotter than 195. Hysterisis is usually about 7 or 8 degrees, depending on the brand of coolant temperature switch.

What exact make and model of pump, motor and solenoid valve does your bus have? I'm now very familiar with my bus's setup after having replaced everything a year or so ago, and most others such as Blue Bird's are broadly similar to mine, but it's well worth you learning all you can about your specific setup to help you troubleshoot.

John
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Old 12-30-2018, 09:30 PM   #3
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Quote:
Originally Posted by Iceni John View Post
Any leak at the reservoir itself should be easy to see and easy to fix - the only connections there are low-pressure return hoses from the motor and power steering, and the feed hose back to the pump itself which is under suction. Or is the fluid coming out the breather? If the inlet sides of the pump or motor are leaking, even slightly, you'll know about it in a hurry! 1500 PSI hydraulic fluid will spray everywhere, and I mean everywhere, from even the tiniest hose pinhole or loose connection. It's safe to assume that your pump and motor do have slight internal leakage, but that should not manifest itself as external leaks because usually the fluid is seeping past the lobes inside, not passing through the external seals. Does your motor have an internal or an external drain system? An old, tired and slightly internally-leaking motor will spin by hand more freely than a new tight leak-free motor - how does it feel when you spin the fan backwards by hand? If you disconnect both hoses from the motor or pump, either should have significant resistance to turning by hand if they are in good condition, but if either can be freely turned by hand then they are probably worn internally. Another thing to check, and something that will reveal if there's mechanical wear within the entire system, is a fluid analysis - iron or aluminum particles in the fluid will prove wear. Is the fluid black, or does it still look like new? Also, is the solenoid directional-control valve leaking?

On my bus the fan runs at half-speed (i.e. with the directional-control valve open and diverting half the flow straight back to the reservoir) up to 195 degrees, then the valve closes and runs the fan at full speed when hotter than 195. Hysterisis is usually about 7 or 8 degrees, depending on the brand of coolant temperature switch.

What exact make and model of pump, motor and solenoid valve does your bus have? I'm now very familiar with my bus's setup after having replaced everything a year or so ago, and most others such as Blue Bird's are broadly similar to mine, but it's well worth you learning all you can about your specific setup to help you troubleshoot.

John
Wow John thanks for the thorough response.

Iím not sure the make and model of the pump motor or solenoid valve.

The fan when spun backward meets resistance almost immediately and if I try to free spin it hits the resistance and bounces back (a good sign it sounds from your description)

What would cause oil to come from the breather on the reservoir?

Would solenoid issues cause leak symptoms?

The motor itself looks newer than the surrounding components so Iím hoping that isnít the failure point.
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Old 12-30-2018, 09:44 PM   #4
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Join Date: Jun 2016
Location: Orange County, CA
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Year: 1990
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Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
It sounds like your fan motor is OK. Good. Ordinarily nothing should ever come out of the breather, unless you've over-filled the reservoir and when the fluid gets hot it expands and comes out. The solenoid directional-control valve will bleed off fluid if its internal valve is worn and allowing fluid to seep past, and that will definitely cause the fan to run slower than it should. At 2100 RPM engine (and pump) speed my fan at full speed is turning at about 1800 RPM, and at half-speed it runs very slowly (or hardly at all) when at 600 RPM low idle. A cheapo handheld non-contact tachometer is useful to measure fan speed.

One thing I did when I rebuilt my entire cooling system was to install two hydraulic pressure gauges to make troubleshooting easier. A 2000 PSI gauge reads supply pressure at the fan motor's inlet, and a 100 PSI gauge reads back-pressure at the motor's outlet before the fluid goes through the cooler and back to the filter and reservoir. If the pump is under-performing or if the motor is seeing too much back-pressure, these gauges will tell me what's happening. Well worth it. (Besides, who doesn't like gauges? I've got 24 so far! Knowledge is power.)

John
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Old 12-30-2018, 09:54 PM   #5
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Thanks again John. The breather shouldn’t be “breathing” out enough oil to cause a low level, so I’d say that is not the cause. The motor I agree seems good also. Would the solenoid poppet seeping be noticable and at a rate of a few quarts per hour? That seems excessive. Is the inlet side at 1500 psi even in low idle?
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Old 12-31-2018, 08:23 PM   #6
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Join Date: Jun 2016
Location: Orange County, CA
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Year: 1990
Coachwork: integral
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
Let's hope that the pump is also OK - pumps and motors usually last for a few hundred thousand miles before succumbing to inevitable internal wear, but their deterioration is usually gradual. If the solenoid directional-control valve is worn and not sealing, it's basically leaking internally, and it will result in some hydraulic fluid being diverted back to the reservoir even when the fan should be running at full speed. The only answer to that is to replace it, but that could be easier said than done. If you have a common brand such as a Parker/Eaton, then all it takes is a trip to your local hydraulic dealer and they can get you a new one. If on the other hand you have some funky old hasn't-been-made-in-a-million-years Danfoss 7W110-2 like mine, I had to hunt far and wide to find a replacement - I found somebody in MN who had five, maybe the last five in existence, so I bought three, one to use and two as spares. For a tenth of their original price it was worth it.

I'm still not sure I understand where exactly the leak is. If you're losing that much it should be clearly visible, and a worn out solenoid valve probably wouldn't be leaking externally at all, let alone that much.

The motor's inlet side will be at about 1500 PSI only when the pump is at full engine RPM; at lower pump RPMs the pressure will be correspondingly less. At 600 RPM low idle my motor's inlet pressure is very low, maybe only a hundred or two PSI, barely enough to read on my 2000 PSI high-pressure gauge. I suspect the relationship between pressure and RPM is more logarithmic than linear, but who knows?

Blue Bird has a useful brief explanation of their hydraulic fan system, most of which applies generically to other makes and models: http://www.centralstatesbus.com/wp-c...s/a3hydfan.pdf And here's Parker's take on it: https://www.parker.com/literature/Hy...ns%20Guide.pdf

HTH, John
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Old 01-01-2019, 04:46 PM   #7
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Quote:
Originally Posted by Iceni John View Post
Let's hope that the pump is also OK - pumps and motors usually last for a few hundred thousand miles before succumbing to inevitable internal wear, but their deterioration is usually gradual. If the solenoid directional-control valve is worn and not sealing, it's basically leaking internally, and it will result in some hydraulic fluid being diverted back to the reservoir even when the fan should be running at full speed. The only answer to that is to replace it, but that could be easier said than done. If you have a common brand such as a Parker/Eaton, then all it takes is a trip to your local hydraulic dealer and they can get you a new one. If on the other hand you have some funky old hasn't-been-made-in-a-million-years Danfoss 7W110-2 like mine, I had to hunt far and wide to find a replacement - I found somebody in MN who had five, maybe the last five in existence, so I bought three, one to use and two as spares. For a tenth of their original price it was worth it.

I'm still not sure I understand where exactly the leak is. If you're losing that much it should be clearly visible, and a worn out solenoid valve probably wouldn't be leaking externally at all, let alone that much.

The motor's inlet side will be at about 1500 PSI only when the pump is at full engine RPM; at lower pump RPMs the pressure will be correspondingly less. At 600 RPM low idle my motor's inlet pressure is very low, maybe only a hundred or two PSI, barely enough to read on my 2000 PSI high-pressure gauge. I suspect the relationship between pressure and RPM is more logarithmic than linear, but who knows?

Blue Bird has a useful brief explanation of their hydraulic fan system, most of which applies generically to other makes and models: http://www.centralstatesbus.com/wp-c...s/a3hydfan.pdf And here's Parker's take on it: https://www.parker.com/literature/Hy...ns%20Guide.pdf

HTH, John

Well after an exciting few days, unreliable mechanics, and gallons of oil. I found the leak. The shaft seal on the motor. Dang that was tricky! It only leaked at highway speed rpms, so recreating the leak in a parking lot was impossible, and after even a quick trip on the highway there was oil everywhere.


Any Leeds on replacement pumps? Hehe
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Old 01-01-2019, 09:00 PM   #8
Bus Nut
 
Join Date: Jun 2016
Location: Orange County, CA
Posts: 849
Year: 1990
Coachwork: integral
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
Quote:
Originally Posted by DMCGARIGAL View Post
Well after an exciting few days, unreliable mechanics, and gallons of oil. I found the leak. The shaft seal on the motor. Dang that was tricky! It only leaked at highway speed rpms, so recreating the leak in a parking lot was impossible, and after even a quick trip on the highway there was oil everywhere.


Any Leeds on replacement pumps? Hehe
Good, I'm glad you found it. Fan motor or hydraulic/PS pump? What make and model is it? As I've alluded to before, if it's a current American brand then parts such as seals should be readily available. If it's a Webster YC motor like mine, I had to have a replacement made to order by QCC - no fun.

It may still be worth your while to install some hydraulic pressure gauges like I did, then if you have too much back-pressure it will clearly show it.

John
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