Monarch 20M Oil Recommendations

I just picked up a 20M and have finished moving it into place and am changing the oils. I believe the manual calls for 30 weight oil. What would be a good oil for the headstock and other locations?
Thanks!

Doing more research it appears Mobil DTE 27 is equivalent to 30 weight. I’ll try to get some pictures posted if the lathe. Feel free to comment on oil recommendations if I’m off on going with DTE 27.

DTE Heavy Medium in my CW16 Monarch for the last 20 years

Same in other oiling places, Vactra #3 on ways and slides and in apron

Have a CM manual if needed that can be scanned and emailed if you want to private message that address

It's true that SAE engine oil (SAE J 300 spec) has an ISO viscosity grade of 100 and that Mobil DTE 27 is also ISO VG 100, but that's it. Mobile DTE 27 is an hydraulic oil and is engineered for very different service than either motor oils or gear oils. Motor oils and hydraulic oils are designed to work with filters and have additives to hold particles in suspension until the filter can remove them. Gear oils are intended to operate without a filter and are engineered to let particles settle to the bottom of the gearbox. Some of the additives the give the best performance in a gear oil are not compatible with the exotic alloys used in some hydraulic systems, so you may not get the best anti-foaming or rust-and-oxidation additives available.

Back when this machine was built, about the only difference in oils was the viscosity and oils had very few, if any additives. Chemical/petroleum engineering has come a long way since.

The correct Mobil oil for the job is Mobil DTE Heavy, which is ISO VG 100. Don't get the DTE Named Series gear oils confused with the DTE 20 Series hydraulic oils; they are very different oils, despite both having "DTE" in the name.

Cal