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rotorwrench · 03-30-2021, 08:05 AM

Marvel Mystery Oil may have been a mystery back in 1923 when it was first sold as an engine cleaning additive but it certainly is no mystery in the modern era. It is simply a light oil with a solvent. The odor gives away the solvent in the mix. The stuff is not rocket science for sure but is is relatively safe to use when the directions are followed. MMO is comparable to ATF mixed with acetone and is likely a better penetrating oil than a lubricant but it does work in pneumatic air tools as a lube & cleaner. Air tools don't have to pull a heavy load and need to operate at high rpm so it won't hurt them at all.

I've heard of folks filling the cranckcase with diesel fuel, kerosene, or other solvents for a short run to clean crap out but that practice can be very risky. I wouldn't recommend putting anything other than engine oil in a crankcase for any length of time.
An engine's oil filter will clean enough crap out to do the job if a person follows good maintenance practices.

The Model A, B, and early V8 engines all could have used the benefit of an oil filtration system but it took Ford a while to incorporate a decent system. Screens work but they have to be cleaned and checked regularly with more frequent oil changes in order to be effetive.

03-30-2021, 08:05 AM	#29
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: Marvel Mystery Oil in Crankcase Marvel Mystery Oil may have been a mystery back in 1923 when it was first sold as an engine cleaning additive but it certainly is no mystery in the modern era. It is simply a light oil with a solvent. The odor gives away the solvent in the mix. The stuff is not rocket science for sure but is is relatively safe to use when the directions are followed. MMO is comparable to ATF mixed with acetone and is likely a better penetrating oil than a lubricant but it does work in pneumatic air tools as a lube & cleaner. Air tools don't have to pull a heavy load and need to operate at high rpm so it won't hurt them at all. I've heard of folks filling the cranckcase with diesel fuel, kerosene, or other solvents for a short run to clean crap out but that practice can be very risky. I wouldn't recommend putting anything other than engine oil in a crankcase for any length of time. An engine's oil filter will clean enough crap out to do the job if a person follows good maintenance practices. The Model A, B, and early V8 engines all could have used the benefit of an oil filtration system but it took Ford a while to incorporate a decent system. Screens work but they have to be cleaned and checked regularly with more frequent oil changes in order to be effetive.