Air compressor oil

[thiggy]

I have an old 3 hp electric compressor and cannot find my owner's manual. What weight oil should I use in the compressor crankcase?

[cabinetman]

I have an old 3 hp electric compressor and cannot find my owner's manual. What weight oil should I use in the compressor crankcase?

Most compressors take 30w non-detergent oil.

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[LCHIEN]

don't they sell generic compressor oil in places like HF and industrial supply houses?

[dbhost]

and Lowes, and Home Depot, and Ace Hardware and... Yeah, compressor oil is all over the place... Check in the tool dept...

[cabinetman]

The OP didn't ask where it was sold, but motor oil would be as easy if not easier to find and would likely cost less than oil marked "Air Compressor Oil". One more thing...make sure it's not an oilless compressor.

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[woodturner]

What weight oil should I use in the compressor crankcase?

Many air compressors use 30w non-detergent oil. However, if you look on the nameplate of the compressor or near the oil filler cap, it may be marked on the unit itself.

In any event, make sure you are using non-detergent oil. Motor oil is not a substitute for compressor oil, and can cause excessive wear and leakage if used in a compressor.

[sweensdv]

........ One more thing...make sure it's not an oilless compressor.

And if it were oilless, just where would you add and drain the oil?

[LCHIEN]

where do you put the air in and how do you know when its full??

Do you have to drain the old air?

What if it's an airless compressor (what else would you use with an airless sprayer)?

[cabinetman]

Many air compressors use 30w non-detergent oil. However, if you look on the nameplate of the compressor or near the oil filler cap, it may be marked on the unit itself.

In any event, make sure you are using non-detergent oil. Motor oil is not a substitute for compressor oil, and can cause excessive wear and leakage if used in a compressor.

Motor oil (30W non-detergent oil) is a substitute for air compressor oil and has no ill effects on their operation. It does not cause excessive wear or leakage. Oil marked "air compressor oil" is not recommended to be used in automotive engines as a substitute for motor oil.

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[thiggy]

Thanks for all your suggestions. I think I will go with the 30W non-deterg, as I already have a few quarts on hand. I of course have already drained and refilled the old air and adjusted the carburettor spring tension.

[woodturner]

I think I will go with the 30W non-deterg, as I already have a few quarts on hand.

That should work fine.

The important part is the non-detergent oil. Detergent oil such as motor oil has "detergents" in it that are designed to dissolve and dislodge particles and dirt, such as wear particles and combustion byproducts (in an automotive engine, for example). Systems designed for detergent oils have a filter to remove these particles so that they do not cause further damage.

To avoid any confusion, by "motor oil" I mean commercially available API certified oil. All current API grades of oil are detergent oil and have been for decades. By current definition, "motor oil" means detergent oil. There terms are sometimes misused or interchanges by the misinformed in casual discussions , but SAE and API define motor oil as detergent oil in current usage (and have since 1951). API-SA oil is a non-detergent oil and is still available for use in antique cars such as the Model T, but is considered "obsolete" by API. For those interested in learning more about the API grades, here is a link
In current usage, API defines motor oil as detergent oil.

In an air compressor, lawn mower engine, or other applications where there is no filter, these particles remain in suspension in the oil and cause excessive wear. That's why detergent oils should not be used in air compressors.

If you have used motor oil in your compressor, though, don't immediately freak out :-) The wear is gradual, and for casual homeowner and hobbyist use, it may take years before the increased wear is significant. If one used their air compressor professionally for a living, they would see the excessive wear much sooner (assuming they knew what to look for and were watching for it), but it appears that is not the case for you or others posting in this thread.

FWIW, if anyone is interested in learning more about oils and their properties, tribology is the study of surfaces in relative motion and includes lubricating oils as well as materials. A search on tribology will provide links to many informative sites. I would also be happy to answer any questions, though we should probably start a different thread if we want to discuss tribology. This research paper explains the properties of the detergents and why they are added to motor oil
detergent motor oil

[cabinetman]

In any event, make sure you are using non-detergent oil. Motor oil is not a substitute for compressor oil, and can cause excessive wear and leakage if used in a compressor.

The important part is the non-detergent oil. Detergent oil such as motor oil has "detergents" in it that are designed to dissolve and dislodge particles and dirt, such as wear particles and combustion byproducts (in an automotive engine, for example). Systems designed for detergent oils have a filter to remove these particles so that they do not cause further damage.

In an air compressor, lawn mower engine, or other applications where there is no filter, these particles remain in suspension in the oil and cause excessive wear. That's why detergent oils should not be used in air compressors.

If you have used motor oil in your compressor, though, don't immediately freak out :-) The wear is gradual, and for casual homeowner and hobbyist use, it may take years before the increased wear is significant. If one used their air compressor professionally for a living, they would see the excessive wear much sooner (assuming they knew what to look for and were watching for it), but it appears that is not the case for you or others posting in this thread.

FWIW, if anyone is interested in learning more about oils and their properties, tribology is the study of surfaces in relative motion and includes lubricating oils as well as materials. A search on tribology will provide links to many informative sites, many of which do not require a Ph.d to understand.

Many of our forum members use air compressors and the oil type should not be misunderstood. Your statement that motor oil is not a substitute for labeled "air compressor oil" could be your misunderstanding when you searched websites for an answer to the question. When rewording your answer from website information, "motor oil" is available in both detergent and non-detergent. Motor oil...per-se, if non-detergent (30w) can be used.

If you have used motor oil in your compressor, though, don't immediately freak out :-) The wear is gradual, and for casual homeowner and hobbyist use, it may take years before the increased wear is significant. If one used their air compressor professionally for a living, they would see the excessive wear much sooner (assuming they knew what to look for and were watching for it), but it appears that is not the case for you or others posting in this thread.

That statement continues the generalization about motor oil, without clarifying the fact that it's the detergent type that may be problematic. The use of the words...motor oil, is too general without the specificity of it being detergent or non-detergent.

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[cwsmith]

And if it were oilless, just where would you add and drain the oil?

Easy, if there is no filler plug... just remove the spark plug and pour it in there!


Even Walmart sells "compressor oil" and I have seen it in Harbour Freight. But, as already mentioned my several other members 30 wt NON-detergent motor oil is highly recommended and is in fact the only recommendation on my little 2-gal lube Craftsman compressor.

I see that you are in the south, so 30-wt should be fine. Up here in the NE, that would present some problems as it would get pretty stiff in the winter and, as I have experienced in my old I-R twin tank, it will cause the motor to trip the breaker.

I hope this helps,

CWS

[cabinetman]

I see that you are in the south, so 30-wt should be fine. Up here in the NE, that would present some problems as it would get pretty stiff in the winter and, as I have experienced in my old I-R twin tank, it will cause the motor to trip the breaker.

I hope this helps,

CWS

Switch to a 20W non-detergent.

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[woodturner]

I see that you are in the south, so 30-wt should be fine. Up here in the NE, that would present some problems as it would get pretty stiff in the winter and, as I have experienced in my old I-R twin tank, it will cause the motor to trip the breaker.

If you could find a multi-weight non-detergent oil, that might be a solution as well, but it will be difficult or impossible to find such an oil, since multiweights are primarily used for motor oil.

Synthetic oil would be another option. The cold temperature viscosity increase of synthetics is at least an order of magnitude less than non-synthetic oils. In addition, synthetics are available for non-engine applications such as manual transmissions and are easier to find in a non-detergent formulation.

You could also use a lighter weight oil, but would eventually see greater wear. However, for light usage it is probably a minor issue - the increase in wear caused by using a lighter oil could take years to become noticeable.