2004 Grand Prix engine swap

I recently had my engine sieze up on my 2004 grand prix gt. While looking for a new engine i was told that i need to get an engine from a 2004 and back grand prix. I was under the assumption that engines from 2004-2008 will work. I found an engine from a 2009 Buick Lacrosse with 20000 miles on it that says it will fit a 2006 grand prix gt. I was pretty sure that it would work with my car but the seller says that he doesn’t think it will. It is the same 3.8 w/o supercharger. Am i wrong or is the seller wrong?

I’ve run into this before with GM engine/computer swaps. You have to make sure that the engine/computer will work together whichever is replaced. The engine will physically fit into the vehicle but you have to make sure it will work with the computer.


The are same L26 3.8L. Theoretically it should just swap right in.

I think there was a change from series 2 to series 3 .8s around that time.

Listen to the seller. He wants to sell the engine. Why would he lie? Also listen to Tester. If you try it, you will have issues. Look at www.car-part.com to find a more compatible engine. There are hundreds out there.

Well the thing is that they are an auto recycler that has multiple of both engines. And the one they say will work costs more. They didn’t say anything about the computer though. Just that i would have to use teh same manifold i think it was if i swapped the engine. Is there any way to find out if it would work without actually putting it in and trying it. From what i can tell mine is a series 3 not a series 2. The reason i don’t want to keep looking is they are mostly more expensive. The one i found is $450 for an engine with 20000 miles on it. They say it would work with a 2006 grand prix. Same body style and all the other replacement parts i have gotten are interchangable between the 2 years but not interchangable with the engines they say i would use. Is there anything that i can look for on my car or on the other engine that would tell me for sure if it would work?

One other think i wanted to mention. When looking for engines and parts it ask for the 8th digit of the VIN. Mine is 2 which as far as i can tell means its the same engine as the rest. But like i said before thats why i am on here asking.

Check with another junkyard, there’s an interchange manual that lists this kind of thing.

Me, I’d take his word for it.

I ran into the same sort of problem swapping an engine between a 1997 Stratus and a 1999 Stratus. They both had the same engine but I was told that they were not interchangeable… I pulled the intake and exhaust manifolds from the 99 engine and bolted them onto the 97 engine and dropped the 97 engine into the car. That was four years ago and it is still running great. Just make sure that the electronics will swap ie. sensors, switches and the like. If it is the same block the internals are likely to be the same. Mechanical is mechanical… It’s the electronics that are being put on modern engines that make them non-interchangeable. They just have to be in the same locations and the same sizes if they bolt into the block etc.

04 motor should be easy to find. But finding one at a price your willing to pay is another matter. You found a 20k mile motor for 450? Way to cheap to believe. Should be 1k at least. I would be worried a newer motor might have different engine mounts or torque brackets on a new car since the engine compartment sheet metal may have changed.

I agree that the price sounds cheap for a 20k miles engine. Hopefully they ain’t lyin’.

As to the interchange, I can’t answer that question. If you live in or near a major metro area you might check with the public library in the reference section to see if they have the Hollander interchange manuals.
If the engine block, cylinder heads, and so on show a match then the peripherals should swap out and make it a direct fit.

I found the cylinder head casting numbers and there are 3 or 4 of them. I’d make sure the numbers on your current heads match the ones of any engine you’re considering.

As for the cost i thought the same thing at first after seeing how much lots of people want for them. But the place i am looking at has a few of them of different mileage. The same engine with 60000-90000 miles on them are the same price. I guess it was$475 not $450. and im not sure if that is with or without any kind of core charge. They are an auto recycler that buys cars from insurance totals and what not. They have a lot of engines from rear end collisions that totalled a vehicle but the engines are untouched. I might have to look for that manual you are talking about.

So update for anyone who is interested. My car is done. I got an engine from a 2009 Buick Lacrosse with 21000 miles on it. It was the same series 3 engine with the vin 2. Knowing that any engine from a grand prix from 2005-2008. May need some things to be swapped between the enigines but it will definately work. I sent it to the mechanic to let him do it instead of doing it myself. Im not sure what all he had to do to make it work but it worked. If i find out what all needed to be done i will update.

I’m happy to see a happy ending. Good job letting us know.

Thanks for the followup.
Happy motoring.

I asked the mechanic what need to be done to do the swap. He had to change some sensors. Not sure which ones. And he shaved down one of the engine mounts because he thought it was too close to the oil pan. Wasnt touching but just a preventative measure. I think he used the same engine mounts and wire harness and everything from the old engine though. Im not driving the car but my mom is driving it 60-70 miles 3 or more days a week. If there is any kind of problem we should definately find out soon but so far i don’t see there being one.