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O&K MH 4 CITY Hydraulic system Trouble!?

A

Alban

New Member
Joined
May 4, 2021
Messages
4
Location
North Macedonia
Hi,
Recently I have been working on a MH 4 City 1996 , it has some trouble with the hydraulic system ,
when I turn on the excavator and the engine runs on low rpm no warning lights come on, giving more throttle the Hydraulic High Temp light lights up , it does as well when we extend the arm ( retract the cylinders ) the excavator sometimes runs fine for up to 30 min , then it looses power...
many electricians have checked the temp sensors and the tank pressure sensor but none of them have fixed it yet...
I haven't been able to find the whole Service Manual anywhere,
how can I check the relief valve and the main hydraulic pump?

we have changed the hydraulic oil , checked the fan and replaced the hydraulic oil cooler( cleaned it as well ) but the light lights up even when the oil is cold ( 20°C ± 5°C ).

8045_9009030950992.jpg
 
B

BillG

Senior Member
Joined
Mar 26, 2009
Messages
510
Location
S. Wisconsin
I have absolutely no experience with this particular machine so i will ask some questions first. Is the sensor a simple electro mechanical type or an electronic type such as a varistor? Has the temperature been checked at the sensor location or just the hydraulic reservoir (maybe the same)? Most of these machines have a thermostatic bypass which prevents oil from reaching the cooler until the oil is at temperature, does the cooler get warm? When the system looses power, how long does it take to reset and will it reset just by turning the machine off for a few minutes? Does it derate (loose power) as soon as the light comes on? Do all functions loose power? Is the light directly controlled by the sensor or is there a control board? Have you bypassed the sensor (depending on type) to see if the problem maybe a shorted wire harness?
 
A

Alban

New Member
Joined
May 4, 2021
Messages
4
Location
North Macedonia
BillG said:
I have absolutely no experience with this particular machine so i will ask some questions first. Is the sensor a simple electro mechanical type or an electronic type such as a varistor? Has the temperature been checked at the sensor location or just the hydraulic reservoir (maybe the same)? Most of these machines have a thermostatic bypass which prevents oil from reaching the cooler until the oil is at temperature, does the cooler get warm? When the system looses power, how long does it take to reset and will it reset just by turning the machine off for a few minutes? Does it derate (loose power) as soon as the light comes on? Do all functions loose power? Is the light directly controlled by the sensor or is there a control board? Have you bypassed the sensor (depending on type) to see if the problem maybe a shorted wire harness?
Click to expand...
It has a pressure sensor and a temp. sensor on the Hydraulic tank, the cooling system is connected in a way that the Fan is driven via Oil , and it starts as soon as the engine starts, and the main hose is directly connected, the cooler get warm safe to touch but not HOT , the system resets if the excavator is turned off for like 15-20 min, yes as soon as the light lights on it looses power it barely moves the arm or the rotate the wheels ( like switching into slow speed ) it has the board computer under the Driver seat all the wires are connected there, they have tried bypassing the temp sensor even the pressure sensor but it was all the same.
https://my-live-01.slatic.net/p/f472cc39a8269738ac7da400c01f517d.jpg_2200x2200q80.jpg_.webp -- the oil temp sensore is similar to this one.
 
A

Alban

New Member
Joined
May 4, 2021
Messages
4
Location
North Macedonia
We have been it a huge loop for over 3 months now , the excavator is out of service but we're unable to fix it, I think maybe the problem is with the main Hydraulic pump , recently i have unbolted the Tank cap where the Hydraulic filter sits pressed down in place by a big spring , in the middle of that Cap it has a magnet and it was full of metallic particles...
 
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