Does Motor Oil Corrode Brass?

[John Hasler]

I did an ASTM copper strip test on four kinds of oil in pursuit of something to use to compound worm gear oil with.
This test consists essentially of soaking a strip of clean copper in the subject oil for three hours at 100C and comparing
the color with a photo of a set of strips.

The test: https://www.google.com/url?q=http://www ... xLveTv7gME


1) Medical grade light mineral oil

2) NAPA ISO 100 motor oil ("single weight")

3) Resolute 5W20 full synthetic motor oil

4) Lucas heavy engine oil additive

According to Lucas this is all hydrocarbons, about ISO 1500 viscosity.

Result: no visible difference among the five strips (the fifth strip was left out in the room air)
My wife could see no difference either (with her opinion about the colors came her opinion about me using the kitchen for this while she was gone).

I'm going to compound my worm gear oil using the Lucas and the synthetic.

[ctwo]

Those seem like common automotive materials, so I would not have expected corrosion, rather less than open air... I am amazed how clean a well maintained (ATF lubricated) transmission looks inside though.

[warmstrong1955]

As far as I know, motor oils & hydraulic oils are all yellow metal friendly.
When you get into gear oils, is when life changes, mostly, when you get into EP (extreme pressure) gear oils...a GL-5 spec. They can also do things to friction materials...ie;wet disc brakes.
EP oils are best suited, and in some cases mandatory, for worm gears, and hypoid gears, which of course, is dependent on the load. The days of SCL type EP (I think SCL is dead....thank you EPA) lubes & even newer mineral oil based types, are going away, and being replaced by synthetic oils. The synthetic EP oils I have used, were all yellow metal friendly. I know of none that are not, but it's always best to ask the manufacturer....something I always did.

Bill

[John Hasler]

Some of the additives in older oils corroded brass and were not to be used in anything (such as manual transmissions) with brass parts: that's partly why the test exists. The manufacturers say that their newer products are not corrosive but it's still widely asserted that you must never use oil with any additives in a worm drive. These assertions are often made by oil manufacturers selling $100/gallon worm oil.

The synthetic oil I tested is labled GL-5. It would be useless for me to try to ask the manufacturer, of course. The results were not unexpected and the experiment a bit over the top considering what I need the oil for but it was fun and I learned a lot about lubrication.

Next up: measuring the 40C viscosity of the Lucas and synthetic so that I can compound a mixture. Need to scrounge some small plastic spheres...

[choprboy]

The answer is probably not, but maybe, and it completely depends on which particular "motor oil" you are using. The same can be said for "GL-5" oils... in that you can't really tell anything by the label.

The corrosion can come from a number of sources, but as warmstrong1955 says, it happens mostly in EP rated oils. The most common way manufacturers get an EP oil is to add sulfur to the mix. GL-4 oils typically have a fair amount of sulfur, but that sulfur is "locked up" in the oil matrix. GL-5 oils (but not all) commonly have an excess of sulfur, which can break down and attack copper-bearing alloys. Most motor oils have very low levels of sulfur (using calcium/zinc/phosphorous and in combination with low-sulfur fuel requirements), but some apparently can have quite a bit (special racing oils/heavy engine oils, etc.).

[John Hasler]

They don't add elemental sulfur. They add sulfur containing compounds such as ZDDP as anti-wear additives. Whether or not a particular compound is corrosive depends on more than just what elements are in it. However, they've been forced to cut way back on sulfur containing compounds lately. Some also claim to have added corrosion inhibitors that negate the effects of corrosive EP additives.

Fortunately, I only need a pint of worm oil and I have several quarts of each of the tested ingredients.

[SteveM]

I am amazed how clean a well maintained (ATF lubricated) transmission looks inside though.

The best penetrant for getting rusty fasteners loose is a 50/50 mix of ATF and acetone, and the acetone is only there to make it flow and creep better.

I have a squirt bottle of it under the bench at all times.

Steve

[John Hasler]

I am amazed how clean a well maintained (ATF lubricated) transmission looks inside though.

The best penetrant for getting rusty fasteners loose is a 50/50 mix of ATF and acetone, and the acetone is only there to make it flow and creep better.

I have a squirt bottle of it under the bench at all times.

Steve

Just about any light oil mixed with acetone works well. WD40 is light oil in a volatile hydrocarbon carrier but I think acetone works better as a carrier. I suppose the best penetrating mixture would have lots of EP additives.

[Mr Ron]

My 65+ year old Sheldon lathe specifies SAE 30 non-detergent oil. It has bronze bearings. Some have recommended a detergent oil, others have not. Based on your experiment with different oils, what would be your recommendation for an oil for my lathe? The straight oil proponents claim a detergent oil will make the bearings "too clean" and cause the bearings to start running dry, especially on an old lathe.

[warmstrong1955]

My 65+ year old Sheldon lathe specifies SAE 30 non-detergent oil. It has bronze bearings. Some have recommended a detergent oil, others have not. Based on your experiment with different oils, what would be your recommendation for an oil for my lathe? The straight oil proponents claim a detergent oil will make the bearings "too clean" and cause the bearings to start running dry, especially on an old lathe.

Non detergent oil is spec'd out in applications where there is no filtration. With non-detergent oil, contaminants will settle out to the bottom of the enclosure.

Detergent oils will hold the contaminants in suspension, so they can be filtered out. No filter....not a good idea, as you will be running any contaminants thru the gears & bearings & whatever continually.
It will not make bearings 'too clean'. As far as coefficient of friction, non and detergent oils are the same, depending on what anti-wear additives are in each. In the mining industry, many, and most, use detergent motor oils in the hydraulic systems. 15W-40 is a favorite. Advantage is reduced wear due to the increased AW ingredients in motor oil compared to hydraulic oils, including AW hydraulic oils, and commonality of oil in different machines & their systems. Makes it harder for a guy to put in the wrong oil in the engine, hydraulic, or transmission systems.

My lathe, and my mill, specify non-d motor oils, and that is what I use in both.

Bill

[John Hasler]

My 65+ year old Sheldon lathe specifies SAE 30 non-detergent oil. It has bronze bearings. Some have recommended a detergent oil, others have not. Based on your experiment with different oils, what would be your recommendation for an oil for my lathe? The straight oil proponents claim a detergent oil will make the bearings "too clean" and cause the bearings to start running dry, especially on an old lathe.

My experiments don't really have anything to do with detergents: those additives have never been accused of being corrosive. Same applies to the viscosity index improvers that make an oil "multi-weight". It's entirely about the lubricity enhancers and EP additives such as ZDDP. I suspect that I've confirmed that modern engine oils (even GL-5 oils) are "yellow metal friendly" (except for some specialty products that brag about extra ZDDP). I only know for sure about the exact products I tested, but that gives me stuff I can use.

However, I don't believe that engine oil detergents (a usage of the word detergent remote from the common meaning) can suspend metal wear particles. Their purpose is to keep particulate products of combustion in suspension. My machines don't produce any of those so I don't care about detergents one way or the other.

[warmstrong1955]

However, I don't believe that engine oil detergents (a usage of the word detergent remote from the common meaning) can suspend metal wear particles. Their purpose is to keep particulate products of combustion in suspension. My machines don't produce any of those so I don't care about detergents one way or the other.

Well....it will. Not only particulates, but metals will stay in suspension. Not as long, but they will. Depends on the down time....BUT....soon as you start things moving again, whether it be an engine or a gearbox, all that stuff is circulating through the system. Non detergent oils do not do that. The stuff settles and stays put.
If you had ever seen what happens to an engine, that was using non-detergent oil, and was changed to detergent oil, you would be a believer. The detergent, does just like it's name, and will clean out all that sludge settled in the pan, the valley and elsewhere in the block, churn it up, and send all that nasty stuff, including metal, thru the bearings, and everything else for that matter. This is ungood.

Bill