You know how to check your engine and, in the case of automatics, transmission oils: just look at the dipstick. The correct — or incorrect — fill level is immediately obvious.
What is not obvious is the condition of the oil itself, so the next time you check take a clean piece of white paper with you. Paper towels or toilet paper are best suited for this operation.
Wipe the dipstick on the white paper and look at the oil residue. Engine oil should be of uniform color, with no particles or "foamy" material. If these are present you need to change the oil and check for coolant leaks. Smell the residue to detect traces of gasoline or "blowby," or the odor of burning oil.
Performing this test with transmission fluid, it too should be a uniform color (usually reddish) with no visible particles or "burnt" color. If it smells burned, it's either been there too long or there is trouble down inside the transmission.
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