Q: Should I buy an Acura tl 2009 with an engine replacement at 70k miles?

If a used engine was installed, to make a wise decision you would need to know exactly how many miles were accumulated on that used engine PRIOR to its transplant to the car that you are looking at. However, if a "new" engine was installed, then you might have the opposite of a red flag which is a good deal but even that depends on whether the "new" engine was actually properly installed according to the instructions. The only real "red flags" in a car purchase are collision damage (whether such damage is repaired or not stay away), rust, abuse, and lack of maintenance. Consequently, the mere fact that a "part", even a part as big as "the engine", was replaced is not important. What is important is whether the part was PROPERLY installed and, in your particular circumstance, if the part was "used", exactly how many miles were on it prior to installation in the present car? And, of course, is the engine presently functioning well (it can be tested and evaluated, to some extent, during an inspection).

With regard to any used car purchase, you want to confirm that the vehicle has NEVER been in a collision (Carfax might be helpful) and that the vehicle does not have any outstanding recall-related repairs. Apart from that, inasmuch as used car repair, maintenance, and restoration costs are highly dependent on the actual, as found, condition of the vehicle, the only way to get a reasonably precise estimate of costs you might face, and also to protect yourself in the transaction, is to request a pre-purchase vehicle inspection. That inspection, carried out by a certified Mechanic, dispatched to your location, will give you the exact data you need to make an intelligent, informed decision about any car. If you look at the just cited link for YourMechanic’s inspection service, you will see a long list of the vehicle systems that must be inspected as well as details of YourMechanic’s inspection methodology. If you need further help, please do not hesitate for a moment to re-contact YourMechanic and we will assist you further in your attempts to make a wise used vehicle purchase.