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Since the 3.9L motors have been around for awhile now, just curious to how reliable they are? I know GM has put them in quite a few cars over the past 6 years, but how are they holding up? Also, are they difficult to work on for service work?

Reason why I ask is I am looking at a 2006 G6 GTP to be a daily driver and it has around 70k miles. The thing is really sharp, but I am a little weary of the LZ9 engine. I have had a couple 3100 and 3800 cars, but this 3.9L engine is new to me. It looks pretty easy to work on as far as normal part replacement (water pump, alternator, spark plugs, ect). Then again anything looks easier than my North* powered Bonneville.
 

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I had an 06 GTP 6 speed that I drove every day. I had very few issues and the ones I had I was able to fix myself thanks to a Haynes Repair manual. I traded it in with 125K miles on it, and it was still running strong on the original clutch. Brakes were my most common replacement. Front rotors warp super easy, my only complaint.
 

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3.9 is about the worst engine you can get in the G6........theres not many people that HAVNT had to have headgaskets replace AT LEAST once at some point or another.....quite a few of them before 30k miles at that....also doesnt get good gasmileage at all if you want a good reliable engine get one with a low mile 3.6 and only use a high quality full syntetic oil...... on occasion the timeing chains have "stretched" when people dont use a good synthetic oil and go by the oil life monitor rather than every 3-5k miles, im at 5k miles on my mobil 1 right now and gonna be changing it tomorrow but the oil life in the DIC still says 78% oil life remaining lol......
 

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my G6 has a 3.9 and its a daily driver since 2006. I haven't had a problem with the engine. I might be one of the lucky one. But I think 3.9 is the best thing for G6.
 

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Me too, good engine, loads of power and gas mileage is ok, I average 24 when I granny it but that's not very often I think it pulls almost as good as a v8


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I have the 3.5 LZ4 which is based and almost identical to the 3.9. My head gasket has been replaced once and now the second one is starting to leak. Gasket problems seem to be common on a lot of GM engines, not just the 3.9 V6.
 

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Discussion Starter #7
3.9 is about the worst engine you can get in the G6........theres not many people that HAVNT had to have headgaskets replace AT LEAST once at some point or another.....quite a few of them before 30k miles at that....also doesnt get good gasmileage at all if you want a good reliable engine get one with a low mile 3.6 and only use a high quality full syntetic oil...... on occasion the timeing chains have "stretched" when people dont use a good synthetic oil and go by the oil life monitor rather than every 3-5k miles, im at 5k miles on my mobil 1 right now and gonna be changing it tomorrow but the oil life in the DIC still says 78% oil life remaining lol......
Seems to me almost every vehicle GM has built in the past 20 years has crappy headgaskets, especially V6 engines, so thats a given. As far as the 3.6vvt goes, I'm pretty sure the oil has nothing to do with the chain stretching. Any synthetic or syn blend oil will work fine, its to lubricate and cool. Oil does not prevent the timing chain from stretching. Keeping the revs under control might, but not different oil. I drive a Bonneville GXP now, so I'm used to crappy mileage. Over 20 mpg would be great, and a 3.9 should be able to do that just fine.

Thanks for the post everyone! Anything else to know about the LZ9?
 

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Seems to me almost every vehicle GM has built in the past 20 years has crappy headgaskets, especially V6 engines, so thats a given. As far as the 3.6vvt goes, I'm pretty sure the oil has nothing to do with the chain stretching. Any synthetic or syn blend oil will work fine, its to lubricate and cool. Oil does not prevent the timing chain from stretching. Keeping the revs under control might, but not different oil. I drive a Bonneville GXP now, so I'm used to crappy mileage. Over 20 mpg would be great, and a 3.9 should be able to do that just fine.

Thanks for the post everyone! Anything else to know about the LZ9?
a forum member with a 3.6 that drives like a grandpa and used no syntetic oil had to have his timing chains replaced at 50k miles or so and he was going by the OLM and 6-8k oil changes i think it was.......... ive used mobil one full syn and race my car all the time and always drive spiritedly.....spun a rod bearing at 36k due to autocross and must not have gotten oil for a sec and sloshed away from the pickup is best we can figure but my chains werent streted at all and i take my engine up to 7k rpm all day every day it has nothing to do with the chains stretching i'm telling you the OIL DOES. and part of it is definately GMs OLM i just changed my oil at 6k miles (normal do 5k but had to go a lil over this time) and the OLM still said 68% oil life remaining.....

the 3.5 and 3.9 are REALLY bad for head gaskets i had to have them replaced in my 3.5 GT 3 times 3.6 really is the best V6 gm makes now lol and it gets good mpgs too i average 20mpg around town driving around agressively.....hell if i go to the drag strip and reset it it shows to be getting 17avg at the track........ and on the highway if i try i can pretty easilly get 35mpg avg 100% hwy at 70-80mph
 

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I have the 3.5 LZ4 which is based and almost identical to the 3.9. My head gasket has been replaced once and now the second one is starting to leak. Gasket problems seem to be common on a lot of GM engines, not just the 3.9 V6.
the LZ4 3.5 and LZ9 3.9 are identicle engines with exception to the cranks stroke and a few other things but otherwise same block and heads etc

also havent seen nearly as many HG failures on the 3.9s that make less than 240hp either (convertible, impala etc)
 

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Is it due to the Dex-cool anti-freeze that's causing all these gasket failures?
not quite sure anymore i know that used to be the cause but im somewhat thinking a lot of it is due to the iron block and aluminum heads.....disismilar metals will expand and contract at different rates and if the head gasket isnt exactly "GOOD" itll allow seapage which will eventually warp the head IMO..... thats my theory anyway as they dont have any of these problems with their all aluminum engine although the dex cool certainly does leave a nasty film/ corosion in the aluminum engine too :(
 
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