Komatsu PC90 Overheating Issue

[John C.]

Correct. Your photo of the monitor in your machine only shows the S and L power modes. The machines with a machine control computer will show HO, SO, LO and FO.

 

[LACHAU]

Sorry for my confusion, but does that mean that my PC90-1 doesn't have a machine control computer?

Correct. Your photo of the monitor in your machine only shows the S and L power modes. The machines with a machine control computer will show HO, SO, LO and FO.

Sorry...so sorry Sir; but I should inform that PC90-1 has 02 controllers : one for PUMP and the other for Engine throttle!!!

 

[LACHAU]

Attached files are Hydraulic and Electric Circuit diagram in PDF format for more convenience reference.

 

[LACHAU]

The other is ENGINE controller.

 

[John C.]

It does not actively stroke and de-stroke the pumps as the engine load is increased or decreased. Do you see a speed sensor in the schematic? We used to see the same thing in the PW90 machines. The power set switch only has two positions, light load or full load. The TVC solenoid pressure is preset so that the engine can't be overloaded. There are no diodes to indicate faults in the systems. My thought process is the someone turned the screw in a bit or there is something wrong with the solenoid valve. It can probably be tested by running a boom up cycle time. If you are getting boom up cycles at 3.5 seconds or less, the pumps are overloading the engine.
Thanks for the schematic! I love that it can be blown up for an easier read.

 

[LACHAU]

It does not actively stroke and de-stroke the pumps as the engine load is increased or decreased. Do you see a speed sensor in the schematic? We used to see the same thing in the PW90 machines. The power set switch only has two positions, light load or full load. The TVC solenoid pressure is preset so that the engine can't be overloaded. There are no diodes to indicate faults in the systems. My thought process is the someone turned the screw in a bit or there is something wrong with the solenoid valve. It can probably be tested by running a boom up cycle time. If you are getting boom up cycles at 3.5 seconds or less, the pumps are overloading the engine.
Thanks for the schematic! I love that it can be blown up for an easier read.

It does not actively stroke and de-stroke the pumps as the engine load is increased or decreased.

In this regard, you're right John! But PC90-1 hydraulic control system also has some other functions.

 

[LACHAU]

Hello everyone, I have a Komatsu PC90 that overheats after about an hour of use. I have changed all cooling related parts such as new radiator, thermostat, cleaned between radiator and oil cooler, inspected fan and foam seals around fan. Nothing has not improved it. I can run without issues if the outside air temperature is cold, but if it gets hotter than about F out, I have to take many breaks and run with hood open.
In the past I have had a leaking engine oil seal into the bell housing from one side and a leaking hydraulic pump seal into the bell housing from the other but the engine seal has been repaired. I still have the leaking seal in the hydraulic pump that is causing me to have to drain the bell housing daily before running.
After reading many posts on here, I am wondering if this leaking hydraulic pump seal is related to my engine overheating issue. Any guidance would be appreciated. I have been dealing with this issue for >10 years. Thanks!
I have had a couple people come out to look at it but they couldn't figure it out. One guy thought it might be a blown head gasket but it doesn't consume any engine oil and I don't have any air or bubbles in my coolant so I think that is ok. Any ideas? (I have seen some similar issues on here and many knowleg members chimed in to help. I look forward to hearing from John C. as well as others.) Thanks everyone!

We may go too far!!! Back to main subject is "OVERHEAT".
Bobby, Could you inform us about MAX Hydraulic pressure??

1. A lot of excavator's overheat due to hydraulic pressure set too low!!!
2. Does the machine get OVER-LOAD at heavy load (Engine speed drop down)???