777F, 777G, and 785D OEM Off-Highway Truck/Tractors Water Delivery System Caterpillar

Illustration 1	g03665736
Side of Vehicle Chassis (1) Hydraulic oil cooler group (2) Guard (3) Fan and motor assembly (4) Bracket

The hydraulic oil cooler group is located on the side of the chassis on the 777G and next to the cab on the 785D.

The WDS hydraulic cooling system is comprised of the:

• Hydraulic oil cooler group

• Hydraulic oil tank

• Hydraulic temperature sensor

• Bypass valve group

• Check valve

Hydraulic cooler group (1) consists of fan and motor assembly (3), brackets (4). Ducting and protective guards (2) may be included on various installations.

Fan and motor assembly (3) is controlled by the display. The cooling fan will operate at startup for 30 seconds. If the fan does not operate as described, the fan system has failed.

Bypass Valve Group

Illustration 2	g03665745
Bypass Valve Group (5) Bypass valve group (6) Check valve

Bypass valve group (5) is located in the cooler hydraulic lines.

Bypass valve group (5) contains a thermostatically controlled valve in order to control the flow of oil through the cooler. The thermostatic bypass is fully open below 57.2 °C (135 °F). When the valve is open, a portion of the return oil is sent directly to the tank. The bypass is fully closed at 65.6 +0/ - 1.2 °C (150 + - /–2 °F). When closed, the valve routes all fluid through the cooler.

As temperature rises above 57.2 °C (135 °F), the valve continues to close the bypass. This action allows for greater cooler flow, until fully closed at 65.6 +0/ - 1.2 °C (150 + - /–2 °F). The temperature sensor in the oil tank measures the bulk oil temperature for the display. At temperatures greater than 65 °C (149 °F) the display stabilizes temperatures by engaging the fan via the cooling fan relay. If hydraulic oil temperature exceeds 93 °C (199.4 °F), a warning is shown on the MD3 display. If the hydraulic oil reaches 100 °C (212 °F), the display will shut down the WDS as a protective measure.

Check valve (6) allows excess pressure to relieve directly to the oil tank to protect the cooler. Relief pressure is 172 kPa (25 psi).