Next, mark a target on the heat exchanger inlet and outlet and number these 4 and 5, respectively. This records the temperature drop across the cooler. The benefit of this step is that if the oil flow rate through the exchanger and the temperature drop across it are known, the actual heat rejection of the exchanger can be calculated.
And if the system is overheating, knowing the actual heat rejection of the exchanger can help determine whether the problem is the result of an increase in heat load (due to an increase in internal leakage, for example) or whether the problem lies in the cooling circuit itself.
For example, if a hydraulic system with an input power of 100 kilowatts is overheating, and the actual heat rejection of the exchanger is 30 kilowatts, then the efficiency of the system has fallen below 70 percent. Therefore, an increase in heat load is the likely cause. On the other hand, if the exchanger is rejecting only 10 kilowatts of heat (which in this example equates to 10 percent of input power), then it's likely there is a problem in the cooling circuit or there is insufficient installed cooling capacity.
Install a pressure gauge or transducer to record operating pressure if one is not already available. If the system is a closed-circuit hydrostatic transmission, install a similar device to record charge pressure.
With that accomplished, now draw up a table like Table 1 to record the date, time, ambient temperature, operating temperatures and operating pressure(s). Note that there is little point in recording the temperature across the heat exchanger if the fan or water pump isn't running. And, charge pressure is relevant only to closed-circuit hydrostatic transmissions.
In terms of compiling this data, it's a good idea to take readings on the hottest and coldest days of the year, and on a couple of average-temperature days in between. This provides a baseline of information. Beyond that, taking readings at regular intervals - each day or shift, for example - can provide early warning of impending problems. And if the system starts to give trouble, taking a set of readings will reveal if the machine is operating outside its normal parameters.
