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mixing grades of oil, Mobil DTE light+ heavy, =medium?

cyanidekid

Titanium
Joined
Jun 4, 2016
Location
Brooklyn NYC
I have 5 gallons of Mobil circulating oil DTE light ISO 32, the machine manufacturer calls for 47, I just got the machine (used Graziano SAG 17, pumped system in the headstock), and am planning on running a batch of oil for a bit, and dumping it, to clean out the headstock and feed gearboxes.

I'm sure running the light won't do any harm, especially in winter, but after the flush, I'm wondering if I can get away with dumping 10% DTE ex. heavy, ISO 150 in with it that I also have in stock to save 200$. do the manufacturers blend grades to adjust viscosity?

any thoughts from the Tribology tribe?
 
No, but it's a good question. I once read an article where Smokey Yunick ran an engine with clear plastic windows in the oil pan and his #1 surprise was how well two different brands of oil stayed separate, even at full temp and 6000RPM. But, if the oil is the same other than viscosity, I wonder...
 
Oil viscosity is not controlled like diluting lemonade or syrup. DTE Heavy mixed with DTE Light will not produce DTE Medium.
 
Yep, it is a bit like combining 1/2" bearings and 1" bearings. You don't get a 3/4" equilivent.

Was hoping someone could bring a little more insight than the above Metaphor.

Good question though, and if we got some good information on the why's and how's....(the oil, not the bearings)

R
 
OK, here's a bit of technical insight, quite simplified but accurate. Ignoring synthetics, "oil" is a bunch of long, generally straight hydrocarbon chains. There's a linear chain of Carbon atoms, with Hydrogen attached everywhere they can be. Generally, two H to every C in the middle of the chain, and 3 H to the end Cs. These chains come in a bunch of lengths. The really short ones are gases at room temperature: methane, ethane, propane (1, 2 and 3 Carbon). The short-but-not-that-short ones are volatile liquids: butane and octane (4 and 8 carbon), for instance. The longer ones are more viscous fluids, and generally the longer the chain, the more viscous the liquid. Fuel oils (diesel) and lubricating oils usually have 16 or more Carbon in their chains. Paraffin wax is at the long end of the length range (roughly 20 to 40 Carbons), which English-usage paraffin is American-usage kerosene, pretty much a light version of diesel.

The refining process sorts these chains more or less by length. (It also does a whole bunch of other stuff I'm not going to address.) However, it is only exact for the shorter lengths. At longer lengths, you end up with a blend of various similar lengths, instead of 100% pure C16H34. Kerosene is usually more highly refined than diesel, but it's basically the same range of lengths heavily weighted to the shorter end of the range 9 to 16 (approximately) Carbons.

All that's high-school chemistry, by the way. Or at least it was in the 70's.

Anyway, when you buy DTE Light, it has some blend of hydrocarbon chain lengths. (I don't know specifically what that blend is.) DTE Heavy has a different blend, with longer chains. If you mix DTE Light and DTE Heavy, you get a blend of chain lengths, but it's not the same blend that Mobil puts into DTE Medium. The mixture has a much broader range of chain lengths, with not especially very much at the sweet spot for DTE Medium.
 
I've mixed hydraulic fluids like this: Chevron Rando 32 with Chevron Rando 46. No issues. I'll put half and half in a jar and stir it up and see if it separates out.

What I wouldn't do is mix different types or manufacturers unless all the API specs matched. Part of those specs is cross-compatibility. I don't know the number- if you did, you could just compare that one API spec and that would tell you if they are compatible.

The additives can interfere with each other- oil that uses zinc-based additives can't be mixed with oil that use a different type.

Oil is cheap, machines are expensive. If you have to mix, do it to get by- but flush and fill with the right oil as soon as you can.

Mixing for the sake of using up oil though- I wouldn't do it. I'd come up with something else to do with that oil.
 
Thank you for that summary of the chemistry, sf. I understood that is what’s going on, the thread title was a bit of a canard, I know you wouldn’t actually make medium weight mixing light and heavy, but I’m still having a hard time trying to think of how you would do any actual damage in such mild service as a lathe.

In a gas turbine, helocopter gearbox, or other high speed high temp high load application, yes of corse, but In a lathe, especially one that isn’t being pushed to its absolute limit 10 hours s day in a production environment, I’m thinking you can totally get away with it.

I think it’s the clutch where it matters most, what would happen? A bit of slippage, inconsistent lockup? How bad can it be? Anyone tried it?

it seems much more important to just keep clean oil in the dam thing! Way too much time and fretting and sweating on here about what oil is the exact match to the manufacturers recommendation of blablabbitybla that is no Longer available...:)
 
it seems much more important to just keep clean oil in the dam thing! Way too much time and fretting and sweating on here about what oil is the exact match to the manufacturers recommendation of blablabbitybla that is no Longer available...:)
That is certainly the case!
 
You can mix DTE Heavy with DTE Light to get DTE Medium. Use a viscosity calculator which you can find online to mix the proper proportions to end up with the final viscosity. I worked for XOM for a number of years on assets that used DTE lubes, and when the regional distributor didn't have enough of a specific grade, we mixed grades according to the in-house lube representative at XOM. Call the XOM tech rep at 1800 662-4525, option 1 then 3 for verification.
 
If you want a serious answer to this question, ask a serious bartender. Not one of those juggling hipster bartenders.
 








 
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