I'm looking at purchasing a high mileage, very well maintained 2006 Grand Prix 5.3 v8. It has 396,000km on the original engine (new tranny). I'm guessing GM put this motor in a number of work trucks, so I'd imagine it has some legs. Other than a compression check and a look at the belts, are there any common failure points that I can check before purchase? Any telltales that the motor is on it's last legs? Anyone have undocumented issues with these cars?

Thank you

  • I am thinking at 400k miles it is nearing end of life. Plan on an engine transplant.
    – Moab
    Aug 31, 2016 at 20:13

1 Answer 1


tl dr: Move along; nothing to see here.

396,000km (246k miles) is a lot of use even for LSx engines. Unless you are getting this for free, I'd pass. There are several reasons for this.

Even though this is a 5.3L engine, it isn't the same as what comes out of the trucks. It's nomenclatured as an LS4 engine. According to this Wikipedia Article, the crankshaft is shorter on both the front and the back of the engine (by over a cm on each).

The block on this is made of aluminum. Unlike most of the truck engines (L33 being different) which come with cast iron blocks, you won't be able to do much in the rebuild department on this block. You could try to bore the cylinders on this, but at most I believe you can only go 0.005" over. If it takes more than that to clean up the cylinders, you have to resleeve. This is a very expensive proposition.

The other thing which is different is, the bell housing bolt pattern is different than a standard Vortec engine, or just about any other LSx motor for that matter. Since it's designed to go in horizontally, it mates up to a different type of transmission. You'd have to get an adapter to make it work.

My suggestion to you is to absolutely PASS on this engine, due to it's oddity and how many kms it has on it. If you look, you can find an LM7 (5.3L Vortec which is cast iron) or even an LQ4/9 (6.0L Vortec which is cast iron). These are all over the junk yards due to them being put into millions of trucks. You can also find them cheap because of this, complete with wiring harness. These engines are completely rebuildable and can be done so quite inexpensively. You should be able to find them just as easily in Canada as I would expect to find them here in the States. If worse came to worse, a short trip over the border could prove fruitful.

  • 1
    I didn't realize the 5.3l in these cars was so different from the commonly available truck engine. I was hoping it was a candidate for an engine swap. Thank you for the detailed answer :)
    – Paulj
    Sep 1, 2016 at 17:27

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