It seems that figuring out how much oil an air compressor needs is a bit of a challenge for some, including me!
Like many questions about how air compressors work or how to fix an air compressor, knowing the make and model of an air compressor can sometimes help, but sometimes, when the manual has gone missing, that’s a problem.
How Much Oil Does an Air Compressor Need?
First, make sure that the compressor in question is actually oil-lubricated not oil-free? Seems silly not to check, yet given that many air compressors on the market today, and particularly those for home and small workshop use, and “lubed for life” from the factory and no lubricating oil needs to be added to them, make sure yours is an oil lubed type.
How do you know?
Take a close look at the compressor pump. For example, the image below shows a small, 2HP air compressor pump.
The red square shows the approximate location of the oil sump on this compressor pump. The blue circle shows the oil fill and oil sump vent cover, and the orange circle shows the site map.
If this pump was “lubed for life” it would not have an oil fill or sump vent port, nor would it have a sight glass.
Oil Sight Glass
The oil sight glass in the image above is the way this compressor pump can be checked to ensure that this pump has enough oil. The image below shows a close-up of a compressor pump sight glass, and in this sump, the oil is as the correct level, which is 1.2 way up the red dot in the middle.
Oil Dip Stick
Like most cars, some air compressor pumps don’t have a sight glass but use an oil dipstick instead. These are typically found as part of the oil fill tube cap, and extend down from the cap into the sump and oil.
The markings on the dipstick indicate the oil level there, and when the oil needs to be added to ensure that the compressor pump has enough oil.
Compressor Oil Check – Alternative Method
In the absence of an oil sight glass or an oil dipstick, and compressor sump may only have two plugs threaded into it.
Typically the top plug is the fill port, and the bottom plug is how old, used oil is drained out in order to make an oil change.
The red circle shows the oil drain from this compressor sump, and the white circle shows the fill port.
When the old oil is drained from the sump, the bottom plug is threaded back in. Then, fresh oil is added via the top port until the oil reaches the bottom of the threads in that hole. Typically, that’s the full mark for this type of oil indicator.
How Much Oil Does a Compressor Hold?
Why do we need to know? Simply, at least as far as I can see, to find out how much new oil is needed to refill the sump after the old oil is drained out? Buy too little, it’s another trip to the store. Buy too much, and you’ll end up with a partial oil bottle hanging around the workshop for how long?
If there’s another reason why a person would want to know “How much oil does an air compressor need” I’d appreciate you providing that information as a comment.
Smaller air compressors with less than 1 HP electric motor may only use 6-8 oz. Others use quarts. How much oil does a specific compressor need? Without a manual, it’s sometimes very difficult to determine how much oil a specific pump requires. These are the steps I’ve used to determine the answer.
Contact the compressor pump manufacturer… an option but often not successful as so many brands of compressors are sold by big-box stores that have no support for the products they sell and store staff may have no idea who actually makes the compressors branded for them.
Another option… if there is still oil in the sump. is to catch the oil as it is drained, and dump it into any container that has fluid levels marked on the outside. If, for example, the oil in the vessel reaches the 7 0z level, I’d acquire a 1/2 quart bottle if available, and if not, a full quart. If the fluid level exceeded a quart, I’d acquire two bottles of oil.
No oil in the sump to measure… then I use the internet to search for “specifications for the compressor (make) and (model)”. This sometimes returns an accessible (means you don’t have to pay for it) manual. Or if you don’t mind paying for a manual, searching for a manual for that make and model will typically get a result, and the manual “should” provide the answer as to how much oil.
If there is no manual available, “drill down” several pages, looking for blog postings, etc. about that specific compressor make and model. Quite often you’ll find that someone, somewhere has asked the same question of an industry or mechanically-related blog, and you can determine it then.
Look also for sales postings for that make and model as if there are some for sale, the seller may have added a page or two from the manual, and the oil quantity may be there.
Failing that, buy a gallon of compressor oil lubricating oil and fill the sump to one of the levels as outlined above. You’ll likely have oil left over, but better that than having a compressor seize up due to insufficient oil.
Overfilling vs Underfilling Air Compressor Oil
Both of these scenarios can be damaging to your air compressor and so you should try to avoid them. Overfilling the compressor will result in internal damage, while underfilling can lead to premature wear of internal components. For more information on this visit this article on compressor oil, which includes useful reader questions and responses.
If you have any questions about how much oil air compressors need, please leave a comment below so that someone can help you!