I would not use anything flammable.
Real ultrasonic stuff- Branson MC-3http://www.cleanosonic.com/mc3-metal-cleaner/
it recommends a 7%-10% solution strength, so a little goes a long ways. It's fairly obvious when you exhaust the chemical because parts don't clean as well or as fast. MC-3 is designed for ferrous, non ferrous and stainless. For nice or finish work, this is what I have and like.
Simple Green works ok. Just don't use it or anything else full strength and think miracles will happen because there's more chemicals in it. It's safer than some other cleaners. Any caustic cleaner like Purple Power that makes aluminum & pot metal castings white will ruin parts, especially if you leave them in there for a long time.
I've done a lot with plain distilled vinegar diluted with water, especially for ferrous items that are more durable than alloy parts. Using diluted Simple Green or vinegar is a good way to eliminate lots of crud before you run it with the more expensive proper chemicals. I've cleaned several large professional kitchen burnt-on & baked-on gas range tops & all related parts plus grills & other professional kitchen equipment with distilled vinegar & water in my larger unit- dirt cheap and very effective. Very cool to have a perfect rings of identical blue flames without hours of lethal oven cleaner soaking and scrubbing.
The cleaning action is done by cavitation- imploding microscopic bubbles of gas within the solution which "scrub" the parts. Whatever chemicals you add only help with emulsifying these released oils so they don't stick back to the cleaned parts. Water alone works pretty well as far as the cleaning but not as well for the emulsifying. Keeping parts suspended off & away the floor and sides of the unit works best. If your parts are too big for the tank and cannot be suspended without touching, it won't clean as well and supposedly can damage the unit. I do larger parts 1/2 in and 1/2 out of the tank, then reverse them to finish cleaning.
1967 Galaxie 500 Red original Q code 428
1967 Galaxie 500 White with Black stripes 428PI clone- car is dead & long gone, sold near Oak Ridge TN 2000, would love to find it.....
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