[jdkskyking]

Spent the morning cleaning out the header tank. Scale buildup and rust! Not fun to remove. Used a pressure washer and finally got rid of the junk. I’ll post pics later. A updated tank is in the future. 

Replaced thermostat with a genuine Caterpillar Water Temperature Regulator and updated temperature sensor. 

Using Caterpillar engine cooling system cleaner and distilled water, I ran the engine for 1.5 hours. 
The engine achieved and stabilized at 190*. 

I had closed the dash heat manifold valves. After an hour of running the engine I opened the valves. The engine temp dropped and eventually recovered and stabilized. 

I’m confident the engine thermostat contributed to the cooling issue. 

I drained the cleaner from the system and have filled it with distilled water. Tomorrow I’ll run the engine to operating temperature, drain, and add new Cat ELC. 

On the Hydraulic Fan front... I replaced the valve that is used to adjust system pressure and returns fluid to the reservoir tank. Until I drive the coach I won’t be certain if there’s a difference how the fan and radiator perform. 

Long and productive day, I’m glad Richard talked me in to working the problem myself. 
JK

The hydraulic manifold has a spool valve controlled by a 12v electric solenoid controlled by the engine ECM. The spool valve determines cooling fan speed, high or low. The CAT-13 ECM removes the 12v at 217° coolant temp. This allows the fan to run on high until coolant temp is reduced. 
There is also a logic valve in the system that prioritizes hydraulic fluid flow between the fan an gearbox. 
There are two pressure relief valves that return fluid to tank, a RV5 and RV6. 
The RV5 valve should be set to 2500 psi to protect the entire hydraulic system. The RV6 valve protects the gearbox and should be set to 2000 psi. The gearbox also has internal pressure relief system.