I also put 3 quarts of motor oil in the car about three
weeks ago on 1994 Mercury Cougar

The oil was very low. Should I be out of oil again because I am hearing a high pitched sound coming from
the motor that I ussually hear when it's out of oil.
What could the problem be?
The last time it was low on oil, I didn't hear that sound.

Asked by for the 1994 Mercury Cougar
you are either using oil or you have a bad oil leak ,either way have your mech ck it out
1 more answer
Maybe you could have a shop check it , before the engine locks up. 'Acceptable' oil consumption on older (high mileage) engines is about a quart every 3-4000 miles , by many standards. You appear to have gone well past that limit.
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