The manual doesn’t say what weight or type of oil to fill it with.
I read on another forum to use 5w-50 synthetic.
Oil for Brute air compressor?
Not knowing the model or seeing a photo makes it difficult to offer model specific recommendations.
If the Brute air compressor is under warranty, use the oil recommended in their compressor manual, as using other oil may void the warranty. Though, as you say, your manual doesn’t specify oil and that’s weird!
If the compressor is past the warranty stage, visit your local big box store and buy compressor lubricating oil. Typically, that will work.
You can, certainly, purchase higher tech, fully synthetic oils, but check the price versus the cost of the compressor. Your compressor may not be worth the investment in the higher oil, unless you are using it often and that’s your judgement call.
Me, I use the least expensive compressor lubricating oil in my smaller, DIY type air compressors, and so far, have never had an issue using it.
Do not use a detergent oil.
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