Trying to find out what motor is in my car

I bought a 1999 Dodge Avenger Sport from another guy. When i had my first mechanical failure i found out the motor in the car was not the standard motor that comes with it. The original motor should be a 2.5L and the previous owner put in a 3.0L. im trying to find a way to know exactly what motor is in my car. Perhaps serial numbers on the motor its self and a website to research it. I need to order some parts for the motor and dont know what im looking for.

Can you take a picture of the engine and post it? As far as I know those 2 engines are not interchangeable.

Order an inexpensive part for each engine size to see which one fits. Would the spark plug type give a clue?

When i had my first mechanical failure i found out the motor in the car was not the standard motor that comes with it. The original motor should be a 2.5L and the previous owner put in a 3.0L. im trying to find a way to know exactly what motor is in my car.

It’s the one right under the hood of course.

Sounds to me like you already know.

It’s not the standard motor.
The previous owner put in a 3.0L.

You had a mechanical failure. Have you asked your mechanic?

Seriously?

The 1999 Dodge Avenger came with 2 motors:

4 Cylinders Y 2.0L SFI DOHC
6 Cylinders N 2.5L MFI

Not sure if that helps, but it might.

There should be some markings on the motor. Normally stamped into the block, either somewhere near the oil pan, or just under the head (I know, the whole block, right?). See if you can find them and post them back here.

The 3L is likely from a Dedge Caravan or Chrysler T&C. I imagine that when the engine was replaced the ECM was changed as well

Engine swapping today is a complete nightmare…Different companies make engines all over the world and sell them to anybody who wants them…Serial numbers stamped into engine blocks?? Not very likely…There may be some casting marks that denote a SERIES of engines, but not the specific model of engine…The exact year and model of engine information was listed on an underhood label on the vehicle the engine was removed from. This information should have been transferred to a durable tag placed on the engine when it was pulled. Reputable salvage yards do this, along with the mileage on the car being salvaged. In your case, with nothing to go on and with a choice of perhaps a dozen similar engines as possibilities, it will take a fair amount of investigation to determine exactly which engine it is…Locate the ECM, the “computer” and trace it back to what engine it belongs to should be fairly easy…

I’ll bet it’s the 3.0L Mitsubishi 6G72. Very similar to the standard 2.5L V6, and will bolt up to the stock transmission as well.