08 Grand Prix needs new engine

My 08 grand prix v6 3800 was having over heating issues so I took it to my local mechanic and he said it has a head gasket issue and he suggests to junk the car or replace the engine. I recently had to transmission rebuilt about a year ago so I don’t want to just junk my car. I want to know how much would a new engine cost and would I be able to put the v8 version of my model into my car.

Why can’t the head gaskets be replaced? Describe the problems that led to the recommendation by your mechanic. I had a car with a warped head, and I solved it by buying a junk yard head, shaving it flat, and replacing the valves and springs. That might be cheaper than replacing the engine. Maybe a surplus head can be used as is.

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He opened up a cap to something and it was rusted and he said this is a sign of a blown head gasket then offered me $300 for the car. I kind of regret going to him because it seems like the car in worst condition than I gave it to him in. It’s not overheating at idle no more but now the engine making a weird noise, and two flat tires some how.

Is this your regular mechanic? Get a second opinion. If the cap is metal, then it’s the radiator. If it’s plastic, then it’s the oil cap and that isn’t rust, it’s oil and water mixed together. The oil cap is black and on top of the valve cover. It’s in the cutout of the gray engine cowl in upper right of the photo below.


GM 3.8L’s are extremely common engines, you won’t have any problem finding one. But a blown head gasket isn’t necessarily a death sentence for an engine. I’d get a second opinion. A rebuilt engine will probably be in the neighborhood of $2k, plus labor. A junkyard engine will be significantly cheaper, but you’re rolling the dice.

They did do a V8 Grand Prix from 2005-2008. However, it never sold well, and consequently, the transversely mounted LS4 is rare. And there’s more to the swap than just dropping in the engine. Your transmission will have be either rebuilt again to HD specs or replaced with a 4T65E-HD, you’ll need new CV joints, the PS pump is different, motor mounts are different of course, a new exhaust system will be required, and you’ll need a new radiator for starters. Basically it’s going to cost more to do a V8 swap than it would just to buy another 2008 Grand Prix V8 outright.


The car also doesn’t turn on no more. This is what he shown me when he was explaining what was wrong with the car.

No you don’t want to spend the money to put a V8 in this old vehicle that did not come with one .
As for cost only the places that give you estamates can answer that .
This vehicle has to be in excellent shape before I would even concider a replacement engine.

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I do not think that you should buy into the bad head gasket/junk the engine scenario at this point.
Basing that diagnosis on what is shown does not mean anything. To me that looks like sludge that can develop from aged engine coolant; especially Dex-Cool.

There are various tests to determine whether or not a head gasket has failed. Compression test, cooling system pressure test, and gasses in the coolant test are some of them. Unless he has done those then he’s guessing or in a worst case scenario; scaring you into selling him the car for 300 bucks.

By not turning on what do you mean? The engine cranks but will not start up or do you mean that you turn the key and nothing happens?

It’s a good example of what I’m looking for near me for $880 for a 05 grand prix ls4, might get a quote from a local mechanic about labor cost. They even have a video of the engine running in the car.

At first it attempted to crank up and was making a loud noise but after that I would turn the key and the lights on the dash try and turn on but doesn’t crank no more. I do feel that I should get someone else to look at it because him offering me $300 for the car was kind of fishy to me.

Hope you don’t mean 4 cylinder by Is4 because that will not just bolt in.

I don’t call that fishy . He has to buy an engine - fix anything else that it needs - has his time to include in the selling price - plus after he is done he will be lucky to make much of a profit on the sale of this thing.

Is the car still at the shop or at your home? If at home did you drive it there? It’s difficult for me to tell at this point whether the engine has problems more serious than a head gasket based on the loud noise comment.
Is the oil level at the FULL mark?

If he did no testing and is basing what he told you on the grunge inside the radiator then the diagnosis is suspect in my opinion.

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It’s the 5.3 L v8 engine, and I will need more stuff ofc but I’m going to get a estimate tomorrow on what all it’ll take.


Installing an engine other than what emission sticker under the hood displays is considered emissions tampering by the EPA.



I was able to drive it home because the shop was like 3 mins away but i could tell it was driving weird, after that I noticed the engine had a weird sound that it didn’t have before so I parked it and didn’t drive it. Once i went to look at it today it made a loud cranking noise and now doesn’t start up. Also, the oil level is full but it just said charge system failure when I attempted to start it this time.

For Pete’s Sake , find a V6 and forget this V8 idea .

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I think that’s fishy too. I would not agree to sell the car to the same person/shop who is diagnosing it as “too expensive to repair”, as they have a vested interest which a neutral third party does not.

Furthermore, even with a blown head gasket/ruined engine, I bet you could get way more than $300–possibly as much as $1000–selling the car “as-is” on Craigslist. I see absolutely dreadful cars, which would have cost $1500 a year ago, going for $3k+ right now.

The “sludge” in the picture is created when Dex-Cool is exposed to air and/or combustion gases, and does not mean the engine is unrepairable. Also, if you do have the car repaired, stop using Dex-Cool. Replace the radiator and all coolant hoses, have the heater core flushed, and use a universal coolant, such as Peak Universal Long-Life.

I’ve had three of the V6 3800 and never had a lick of a problem with either of them. 350,000 on one, 520,000 on another and 120,000 on the other one. Most I had was a timing chain and the mechanic also told me the engine was shot and wanted to buy the car because he had a good engine. Cost me $125 in parts and a tow to put it back on the road. These are Bullitt proof engines but still I don’t like taking engines apart.

The 3.8 is one of the best engines ever built. I read a story some years ago that GM had plans to phase the 3.8 out but after a lot of discussion decided to keep it in production for a while longer.

My point earlier was that if this mechanic did no testing and gave you that diagnosis based simply on the sludge in the radiator then what he says should not be trusted.
I’ve seem signs of that sludge in my Sonoma’s radiator and have seen it in my son’s Camaro in the past. Entirely normal but gone completely since the Dex-Cool was ditched.

There is simply not enough known to be able to tell what is going on with your car.