10-05-2025, 02:33 PM
If I recall….
When the engine coolant temperature is in the normal range, the engine ECM provides a 12v DC current to a relay in the engine bay electrical box, mine is accessed from the right side engine bay door.
The relay then provides 12v current to the spool valve solenoid and in turn the system runs on low. On my 2005 version, during normal/low speed operation the fan rpm is 1/2 the Cat-13 engine rpm. I used an optical rpm gauge to determine my fan speed.
Note: During our discovery phase, Joplin Missouri Caterpillar found that my C-13 ECM was NEVER programmed to provide the 12v DC current to the relay.
Newell jumped the solenoid relay and guess what…. My fan ran on low speed. In other words mine too always ran on high…. And I also know why… hint, fan blade pitch set to the minimum pitch because the VICKERS V20 hydraulic pump can’t handle anymore pitch… not enough fan pitch = not enough air to cool the system…anywho… Cat programmed the ECM and at a coolant temp of 217° the 12v is removed to the solenoid system and the fan goes to high. On my rig 217° is way past the point of no return so I installed a temp sensor in the coolant system that catches it at 212°… I also re-pitched the fan blades to 25° but there are consequences to doing that that you should be aware of should you choose to do the same.
Back on topic.
On mine, high fan speed equals the engine rpm.
The first thing I would check is if you have power to the solenoid.
If I recall, Newell replaced my Solenoid during the early days of troubleshooting.
If the solenoid isn’t functioning the system will always run on high, the failsafe mode in the event of a failure in the solenoid system…
If there is no power, then more investigation must occur.
So you know… in my 2005 version “Gold Block”. In the normal mode the steering circuit is prioritized. Thats a good thing right? I have video of the cooling fan stalling as I make turns.
In “HIGH MODE” all of the hydraulic fluid/pressure/flow is redirected to the cooling fan motor and the Steering Gearbox gets what is left over….
Two additional items to know, the gold block has two pressure relive valves, a RV5 that protects the entire hydraulic system by sending fluid back to tank, and a RV6 valve that protects the ZF steering gearbox. The pressure values are stamped on the block body.
SIDE NOTE: The ZF Steering Gearbox has built in internal pressure relief valves so the RV6 is an extra measure of protection.
Start with 12v power and go from there.
JK
When the engine coolant temperature is in the normal range, the engine ECM provides a 12v DC current to a relay in the engine bay electrical box, mine is accessed from the right side engine bay door.
The relay then provides 12v current to the spool valve solenoid and in turn the system runs on low. On my 2005 version, during normal/low speed operation the fan rpm is 1/2 the Cat-13 engine rpm. I used an optical rpm gauge to determine my fan speed.
Note: During our discovery phase, Joplin Missouri Caterpillar found that my C-13 ECM was NEVER programmed to provide the 12v DC current to the relay.
Newell jumped the solenoid relay and guess what…. My fan ran on low speed. In other words mine too always ran on high…. And I also know why… hint, fan blade pitch set to the minimum pitch because the VICKERS V20 hydraulic pump can’t handle anymore pitch… not enough fan pitch = not enough air to cool the system…anywho… Cat programmed the ECM and at a coolant temp of 217° the 12v is removed to the solenoid system and the fan goes to high. On my rig 217° is way past the point of no return so I installed a temp sensor in the coolant system that catches it at 212°… I also re-pitched the fan blades to 25° but there are consequences to doing that that you should be aware of should you choose to do the same.
Back on topic.
On mine, high fan speed equals the engine rpm.
The first thing I would check is if you have power to the solenoid.
If I recall, Newell replaced my Solenoid during the early days of troubleshooting.
If the solenoid isn’t functioning the system will always run on high, the failsafe mode in the event of a failure in the solenoid system…
If there is no power, then more investigation must occur.
So you know… in my 2005 version “Gold Block”. In the normal mode the steering circuit is prioritized. Thats a good thing right? I have video of the cooling fan stalling as I make turns.
In “HIGH MODE” all of the hydraulic fluid/pressure/flow is redirected to the cooling fan motor and the Steering Gearbox gets what is left over….
Two additional items to know, the gold block has two pressure relive valves, a RV5 that protects the entire hydraulic system by sending fluid back to tank, and a RV6 valve that protects the ZF steering gearbox. The pressure values are stamped on the block body.
SIDE NOTE: The ZF Steering Gearbox has built in internal pressure relief valves so the RV6 is an extra measure of protection.
Start with 12v power and go from there.
JK
Kristi & Jeff King
Bentonville, Arkansas
#744 2005 45’ Newell Coach
ZF Suspension/Rear Axle Steering
CAT-13 ACERT KCB Engine 525HP 1642 ftlbs Torque Cat Compound Turbocharger System Producing 49 psi
Allison HD4000MH Transmission with PTO drive for Second Hydraulic Pump.