A quarry operation reported that a Volvo L220H wheel loader was frequently triggering a "Transmission Temperature High" warning light, forcing the machine to derate and slow down. The operator noted that the issue occurred mostly when traveling downhill from the crusher to the stockpile. The transmission oil level was correct, and the external cooler fins were clean.
The technician connected the Volvo diagnostic tool (VCADS Pro) to read the live transmission data. When the machine was traveling downhill, the retarder pressure (used to slow the machine) was spiking to 150 psi, but the transmission temperature was rising rapidly. However, when the machine was working on flat ground or carrying a load uphill, the temperature remained stable.
The Volvo L220H utilizes a hydraulic retarder integrated into the transmission to assist with braking. The oil flow for the retarder passes through a dedicated section of the transmission oil cooler. The technician removed the retarder control solenoid valve on the transmission valve body. The valve spool was found stuck in the open position due to a small piece of rubber O-ring debris. When the machine was coasting downhill, the stuck valve was applying the retarder partially, creating massive internal heat within the transmission fluid.
However, the heat wasn't dissipating. The technician performed a flow test on the transmission oil cooler. The flow rate was significantly lower than spec. The cooler core was removed and pressure-tested; it was found to be internally clogged with a thick sludge. This sludge was restricting the flow just enough that the added heat from the stuck retarder valve couldn't be cooled efficiently.
The repair involved replacing the retarder solenoid valve and flushing the transmission cooler with a specialized solvent to remove the internal sludge build-up. The transmission oil was changed, and the filter was replaced. After the repair, the machine could travel downhill all day without the retarder overheating the system, and the temperature gauge held steady at 85°C.
