What kind of temperatures do you see on your excavators' hydraulic oil? When pushed hard, my 800 runs above 70 degrees Celcius, which I think is around 160 degrees Fahrenheit, and will go up to 78, which my operator thinks is a bit hot. Is this a safe temperature for the hydraulic oil? We only use the Hitachi Super EX 46HN synthetic oil and the outside air temps here now is around 90*F. Any thoughts?
Generally on most systems that have an alarm function for hydraulic oil temperature it will activate at 90+ DegC, often 95 DegC. I think you should be safe at 78 based on the ambient temperatures in which the machine is working. As always when working in really hot/humid climates make sure the radiator and hydraulic oil coolers are really clean, can't stress that enough. BTW, your Hitachi EX46HN is not a synthetic hydraulic oil, it's a mineral-based zinc-free oil. If you want a cheaper option, Conoco Ecoterra should be your choice, it meets Hitachi spec and is about 2/3 of the price.
Hey thanks Nige. This is very helpful advice. We try to wash the cooler/radiator out just about every day with fresh water, as we are working in a salt air environment and we tend to be particular about maintenance. I was just about to order two drums of the 46HN oil (which retails for over $900.00 a drum from Nortrax) so I will look for the Conoco Ecoterra instead. Thanks again.
250°F or 121°C is the maximum allowable temperature for hydraulic oil. Over that temperature, o-rings and seals will go hard and fail after an extended period. Bearings are seated on "interference fit" shafts by heating to 300°F or 149°C. So, over about 275°F (135°C), interference-fit bearing races will want to start to turn on their shafts, thus creating terminal damage when the inner race commences to wear the surface it is supposed to be held tight by. Hydraulic oil temperatures on machinery working in the interior of Australia often run at 250°F (121°C) or more. I have seen hyd tanks where the paint was blistered with the heat of the hyd oil. That's hot, and that's unacceptable. Damage is being caused at those temperatures. I had to install massive air-to-air oil coolers on my Liebherr 974 and 984 excavators, because the hydraulic oil temperature often exceeded 250°F (121°C). The other factor is that the oil film surface begins to break down at temperatures in excess of 250°F (121°C). In an engine, an oil temperature in excess of this can start to cause big-end and main bearing failures. In hydraulics, the oil film failure will cause metal galling and hyd pump failure. A temperature of 230°F or 110°C is about the maximum you should be operating hydraulics at, for any extended period.
In the 30+ years I have been around excavators, the rule of thumb on hydraulic system temperature on a machine with a properly designed and properly operating hydraulic cooling system has been 100° F (38° C) over ambient temperature.
Thanks very much guys. This all makes me feel much better as we are clearly operating below the higher end of the range. Thanks again for the info.