How hot is too hot for hydraulic oil?

Contributed by Mark ‘Manyletters’ Pszczolkowski, Senior Hydraulics Consultant, CD Industrial Group Inc.

When I first moved to Canada, people asked about what is normal. I come from an area where I thought cold was cold and found out that cold was different in northern Canada. So I experienced the same thing when I went down to Texas. And the first time I was down there, guys asked that same question. How hot should a system run? And I was used to Canada.

I’m used to saying “Well, look, if we can get a system to run about 120° F, I’m really happy. But realistically, 140° F is a good number to shoot for.” Well, they all laughed at me and I knew I’d said something silly. So I asked them why and they said the ambient temperature here in July is 120° to 125° F.

Okay, so let’s think about that, right? They asked me how come you always point in Canada when you build the oilfield equipment? How come you always point the radiator onto the hydraulic tanker? Seems stupid that it would get hot right from that. It’s not so stupid when you come to Canada in February. We’re looking for every ounce of heat we can get.

The average person can hold their hand on a tank that is about 140° F maximum. Tougher guys, of course, welders, those guys, will always do a little more. If you can’t keep your hand on it, you need to start looking for a number. Well, the next number to look for is what type of shaft seals on hydraulic pumps and motors are you using because they will have maximum limits, and if your tank is at that temperature, then I’ll guarantee you components within the system are gonna be even higher.

For hydrostatic drive systems, they’re gonna run a little hotter. So 160° F is a good temperature to shoot for. So if you can know, find the tag number for the pump and use that — because if you can get the tag number for that pump and look up a specification sheet, the manufacturer of that pump is going to have guidance for the right viscosity of oil and the temperature ranges, and that could be some data that could help you get re-established if you’ve got no manual.

Most people, when we talk about temperature, they’re trying to see how hot can they run it, rather than work in the opposite way and seeing how cool can they get it to run — and what’s causing the heat to build up in the system in the first place. Those are all things you have to spend some time and learn.