A new client consulted me about the hydraulic oil turning black, smells bad and is depositing varnish in the Hitachi EX5600 excavators he is responsible for. These are BIG diggers. Twin Cummins QSK50s with 4 main pumps (250 GPM) on each engine. Bucket capacity is 40 tons. And a 240 ton dump truck is loaded in 6 passes, in around 3 minutes. Well that’s the machine’s performance target anyway, which the operators hit 90% of the time.
When I inquired about the hydraulic system’s operating oil temperature I was told normal operating temperature is 200ºF (93ºC) and the high temperature alarm goes off at 225ºF (107ºC) when the heat exchangers plug. When that happens the operator is supposed to stop digging and let the machine cool down!
By any measure these numbers are HOT. And plenty hot enough to accelerate oxidation of the oil and deposit varnish. But that’s not the end of it. Heat is a contaminant. And a hot-running hydraulic machine is an unreliable hydraulic machine. This mine is doing oil analysis; monitoring the oil’s acid number and particle concentrations, but at the same time are oblivious to the fact that these machines are running way too hot for optimum reliability. Reminds me of a lyric from the Midnight Oil song: “How do we sleep while our beds are burning?” This machine is cooking itself. But as long it’s loading a truck every 3 minutes we’re good… for now.
The other thing about high operating temperature is, the solution to the problems it causes is essentially another problem: getting the operating temperature down to 176ºF (80ºC), at least. This is not usually something that can be done by flicking a switch. And if it’s hard to do, it often doesn’t happen.
But the fact of the matter is if a hydraulic machine is allowed to run hot, everything else you do will be in vain. In 80/20 terms, hot-running is a ‘little 20’ issue responsible for the ‘big 80’ of reliability problems and the nasty repair bills that follow. And to discover 6 other costly mistakes you want to be sure to avoid with your hydraulic equipment, get “Six Costly Mistakes Most Hydraulics Users Make… And How You Can Avoid Them!” available for FREE download here.