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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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nly use a high quality
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......
None of this is true, but I'm curious to know where the 'facts and statistics' that misled you are coming from. I'm quite sure you are wrong saying '3.9 is about the worst...".

The 3.9L, 3.6L and 3.5L V6 engines are all based on GM's 60-degree "High Value" platform and are identical except for displacement and the addition of VVT in the newer 3.6L and 3.9L. Before I bought our 2008 G6 GT w/LZ9 3.9L I went to Consumer Reports and looked up engine reliability on ALL of the GM platforms that used the 3.9L (LZ9). EVERY ONE of them was rated highest in reliability for 'Engine Major'. All the way back in 1984, my Pontiac 6000STE had one of the first 60-degree V6 engines (the 2.8L HO) and I put over 260,000 miles on that engine with nothing more than routine maintenence and Mobil One Synthetic oil.

Re: "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......"

This means you don't comprehend how the car calculates remaining oil life.

Most of us know by now that modern synthetic motor oils can last much longer than 12 or 24 months 'in the crankcase' and up to 25,000 miles depending on how the engine is being run. If you are running lightly loaded highway miles and spinning only 2,000 rpm at 70 mph, then there is no reason to change oil based on the old months/miles recommendations -- those who do are silly.

You already know that transmission lube replacement depends on severity of service, the same is true for engines. The advantage of computerized engine control is that we can monitor how hard the engine is being run and adjust oil change intervals accordingly. Over-the-road truckers and heavy-duty diesel applications (marine and construction) have been doing this for 50 years.

I would like to know where you heard about the 3.9L engine problems -- Head Gaskets??.

Please be specific.
 

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I've not heard of widespread head gasket failures on the LZ9. Most of the leakage issues seem to involve the coolant crossover pipe gaskets and the front main seal, neither of which are terminal.

Just an FYI though, the 3.6 (LY7) is a twin-cam engine (with aluminum heads and block) from the "High Feature" engine family. The "High Value" family that the LZ9 belongs to are pushrod engines (aluminum heads and iron block) that dates back to the first 60 degree V6 used in the Chevy Citation and its "X" body siblings. I believe that the LZ9 is the last iteration and even though it's eclipsed by the newer twin-cam designs, it's really quite a capable and willing engine with the VVT that you mentioned and roller rockers. I'm not disappointed in mine at all. Take care and good luck. - Mark
 
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