You have a leak and you are getting air into your sysyem. Does your system ever howl, especially at low speeds and turning sharply. If so then you probably have a leak on the low pressure side. Go to the car wash and blast the hoses and box etc. with soapy water and then rinse.. Drive it about 15 minutes and then lay cardboard on the driveway and place your car on the card board and let it run for 15 minutes and then look to see what area the leak/s are coming from. Changing your filter(John's idea) is a good idea and easy to do.. Please let us know what you find....I discount water because you have been replacing your fluid so fast that it can't be water...Jim

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James A. Harris