In my quest to find the right oil for my old horizontal mill, I got hung up on which ISO 68 oil I should use for the machine: Mobil DTE 26 or Mobile DTE Heavy/Medium. Internet research brought up a number of opinions about the subject regarding why to use one oil over another. Finally, I contacted Mobil's industrial lubricants department where a representative took the time to speak with me about the oils in a little more detail. I will attempt to remit the information given to me, as well as dispel false information I gathered during my research. Know that I spoke with the representative specifically about DTE 26 and DTE H/M, but he confirmed that differences stay overwhelmingly consistent throughout the DTE line of oils.
DTE 26 is marketed as a hydraulic oil while DTE H/M is marketed as a circulating oil. This makes it sound like they are significantly different, however, with relation to the use in an old machine tool, these differences will likely have a minimal, and likely negligible, affect.
Both DTE 26 and DTE Heavy/Medium (DTE H/M) have what are called "Anti-Wear" additives. It was explained that this additive "sticks" to the metal surface. Upon two metal surfaces coming into contact, the anti-wear "coating" is sacrificial, and is scraped off of the surface instead of the metal. In case it is not obvious, this helps reduce wear on all the components lubricated by the product (including clutches). DTE 26 does contains more of this anti-wear additive than DTE H/M. It was discussed as to whether or not this anti-wear additive is bad for clutches. The rep noted that only for extremely sensitive clutches, (like say, where two parts need to engage extremely fast in an indexed fashion) often only found on late model machines, would it make any practical difference. He worded it where its not going to make an old clutch simply slip and stop working, nor will it make it have a 1 second delay in actuation. It is more like the clutch may get an additional 2 milliseconds of time before it engages as opposed to an oil that did not have this additive. For old machines like mine, this was not a concern.
Note that the anti-wear additive described above is NOT EP (extreme pressure) additive. EP additives operate differently than anti-wear additives and can have some non-trivial negative effects on certain clutches. Neither DTE26, nor DTE H/M contains EP additives.
Additionally, both DTE 26 and DTE H/M are non-detergent oils. This means that both will allow suspended sediment to settle to the bottom of a sump in an equal manner.
So with so much the same, why would you use one over the other? Again, with respect to old machine tools, there is very little practical difference, however, there are some situations where this could play a factor. It was described to me that almost all of these situations would occur on machine tools manufactured post mid-eightees.
First, if your machine happens to have a high wear items (generally a hydraulic pump, and more specifically, a vane pump), it may greatly benefit from the additional anti-wear additives of DTE26. Newer machine tools have components that are built to tighter tolerances with the expectation it will have these larger doses of anti-wear additives.
Alternatively, if your machine has close tolerance valves or tight passages that see high temperatures, the additional anti-wear additives of DTE 26 can actually burn and leave ash residue in these areas, causing problems.
DTE H/M does have additional defoamants, which may make it more suitable for environments prone to foaming (for instance, an 8000RPM gearbox with an oil bath).
Finally, DTE H/M does a better job of water separation. I believe it is technically a "turbine oil" even though the rep mentioned it is unlikely they would recommend this specific oil for that application.
The cliff notes:
Both oils have anti-wear additives, no EP additives, and no detergents. For an old machine tool (pre mid-eightees), the performance between the two oils is negligible. Even the additional anti-wear additives of DTE 26 is hardly a factor. It was suggested that first, pick which oil is cheaper in your area. If they are the same price, then base your decision on if you already have a different machine running one or the other. Finally, if all else was equal, the rep suggested DTE H/M simply because it had less additives that an old machine tool was not engineered to necessarily utilize.
DTE 26 is marketed as a hydraulic oil while DTE H/M is marketed as a circulating oil. This makes it sound like they are significantly different, however, with relation to the use in an old machine tool, these differences will likely have a minimal, and likely negligible, affect.
Both DTE 26 and DTE Heavy/Medium (DTE H/M) have what are called "Anti-Wear" additives. It was explained that this additive "sticks" to the metal surface. Upon two metal surfaces coming into contact, the anti-wear "coating" is sacrificial, and is scraped off of the surface instead of the metal. In case it is not obvious, this helps reduce wear on all the components lubricated by the product (including clutches). DTE 26 does contains more of this anti-wear additive than DTE H/M. It was discussed as to whether or not this anti-wear additive is bad for clutches. The rep noted that only for extremely sensitive clutches, (like say, where two parts need to engage extremely fast in an indexed fashion) often only found on late model machines, would it make any practical difference. He worded it where its not going to make an old clutch simply slip and stop working, nor will it make it have a 1 second delay in actuation. It is more like the clutch may get an additional 2 milliseconds of time before it engages as opposed to an oil that did not have this additive. For old machines like mine, this was not a concern.
Note that the anti-wear additive described above is NOT EP (extreme pressure) additive. EP additives operate differently than anti-wear additives and can have some non-trivial negative effects on certain clutches. Neither DTE26, nor DTE H/M contains EP additives.
Additionally, both DTE 26 and DTE H/M are non-detergent oils. This means that both will allow suspended sediment to settle to the bottom of a sump in an equal manner.
So with so much the same, why would you use one over the other? Again, with respect to old machine tools, there is very little practical difference, however, there are some situations where this could play a factor. It was described to me that almost all of these situations would occur on machine tools manufactured post mid-eightees.
First, if your machine happens to have a high wear items (generally a hydraulic pump, and more specifically, a vane pump), it may greatly benefit from the additional anti-wear additives of DTE26. Newer machine tools have components that are built to tighter tolerances with the expectation it will have these larger doses of anti-wear additives.
Alternatively, if your machine has close tolerance valves or tight passages that see high temperatures, the additional anti-wear additives of DTE 26 can actually burn and leave ash residue in these areas, causing problems.
DTE H/M does have additional defoamants, which may make it more suitable for environments prone to foaming (for instance, an 8000RPM gearbox with an oil bath).
Finally, DTE H/M does a better job of water separation. I believe it is technically a "turbine oil" even though the rep mentioned it is unlikely they would recommend this specific oil for that application.
The cliff notes:
Both oils have anti-wear additives, no EP additives, and no detergents. For an old machine tool (pre mid-eightees), the performance between the two oils is negligible. Even the additional anti-wear additives of DTE 26 is hardly a factor. It was suggested that first, pick which oil is cheaper in your area. If they are the same price, then base your decision on if you already have a different machine running one or the other. Finally, if all else was equal, the rep suggested DTE H/M simply because it had less additives that an old machine tool was not engineered to necessarily utilize.
