Check your vehicle manual. Your manufacturer has stated how often you should have an eagle transmission check your vehicle. For most new vehicles, transmission fluid must be changed ever 100,000 miles, and 30,000 miles after. However, schedule changes if you use your vehicle for towing, because that will require you to replenish your fluid earlier than expected. Additionally, you must also go to Eagle Transmission for normal check-ups in order for us to see if you have missed some leakage or if the filter is already damaged.