GM V-6 and Intake Manifold Leaks

adc100adc100 Member Posts: 1,521
edited March 2014 in Chevrolet
I added this topic because bits and pieces of it have appeared elsewhere. I think it is a huge problem. Certainly it is worse than the Toyota Sludge Issue (possibly imagined). Anyway I am on my second manifold leak on my second Corsica. The first one at 126K and this one at 76K. I intend to pursue the issue with GM and if I get no satisfaction I'll see 'em in court. I'm retired and have the time. Even if I get no free work-It'll cost 'em lawer money (along with me). I know part of the problem is the antifreeze. They had to come out with one which did not attack the manifold gasket-Dex-Cool. I'm not sure the Dex Cool solved the problem as I was told by the Chevrolet Dealer in Oxford N.C (cant remember name)that this is still occurring in the V-6 3.4 and 3.1 (I would also guess the 3.8-but don't know for sure). I would appreciate good factual information and hopefully this will not generate into a "sludge board"



  • 0patience0patience Member Posts: 1,712
    This is a problem with ALL aliuminum and "plastic" manifolds. I have seen several replaced because they wouldn't stop leaking.
    The 3.8 series II is actually worse.
    The one on my wife's 99 Lumina with the 3.1, the intake gasket let loose at 50,000 miles. We have an extended warranty and it paid for it all.
    Sorry, but it isn't so much a problem with the coolant as it is with the expanding and contracting of the aluminum.

    You would not believe the amount of vehicles that came to me in the late 80s, because they were diagnosed with blown head gaskets. Every one of them, the intake manifolds had "worked" themselves loose and popped the gasket.
    These problems didn't come about until they started using the aluminum intake manifolds.
  • lbthedoglbthedog Member Posts: 198
    I guess I'm wondering how you'll "take em to court" when you've gone so far past warranty. The second poster is closer to the truth. Expansion rates of aluminum and the ability of gaskets to seal has been a hit or miss proposition. The gaskets have to shrink and expand as the aluminum and bolts holding the whole thing together do the same. Retaining torque as bolts stretch is another problem. The 3.8 plastic manifolds had problems when EGRS screwed up and high heats came into play.

    It's not fair to compare this to the Toyota issue which is about Toyota not honoring a warranty. This is more about high mileage engines and what sometimes fails.
  • mastermechanicmastermechanic Member Posts: 31
    Is your odometer going backwards? What year is your Corsica? "The first one at 126K and this one at 76K." Who changed the gasket, you or someone else? A few things, those bolts are not a high torque specification. On mine, they are just over hand tight. I think they are around 10-19 foot-pounds. They are supposed to be torqued in sequence. Make sure that both surfaces are spotless. Don't use a scrapper to clean them. You'll have a grove and then you will really have a leak. I used steel wool. Aluminum loves to warp over time. You need to have the intake checked, and if you have a warped intake, you need to take corrective action.

    Your posting indicates a lot of miles on your vehicle. What year it it? I have a 93 3.8 and a 96 3.1 with no leaks on either. Of course I just overhauled the 3.8( the apv not the car.) runs like a watch.
  • mastermechanicmastermechanic Member Posts: 31
    I just got done fixing a coolant leak that I had. The vehicle is a 1993 Chevrolet Lumina APV 3.8L.

    At first, I thought that the leak was coming from the water pump. I then concluded that since the area below the water pump was dry with no water leaking below it, I assumed that the leak was down farther around the freeze plug. Using an inspection mirror, I concluded that the freeze plug was not the problem either. Someone suggested that I use some of that "Engine Block." They said that the have used it for blown head gaskets and it worked. I tried it and it seemed to work for awhile, but then the leak got worse.

    I then performed an extensive inspection between the area behind the water pump and the power steering pump. With the engine running, I saw a trickle of coolant coming from the approximate area, but I could not pinpoint the leak. I concluded that I had an intake leak because I was also experiencing a sluggish performance with the vehicle which would occur in a fuel/water mixture.

    On Friday, I decided to dismantle the intake with the intention of replacing the lower intake gasket. I got as far as removing the alternator when I saw that the leak was not the intake gasket, but a cracked heater hose outlet. It turns out that initially GM used a neopream(sp?) (plastic) outlet connector that screws right into the aluminum intake. What those engineers were thinking when they decided to use that type of material is beyond my scope of compression. I figure someone's brother-in-law owns the company that manufactures that P.O.S.

    Since the crack was in between the manifold and the nut part of the molding, unscrewing it was out of the question. To make matters worse, the extreme heat melted that P.O.S. to the manifold, much like melted cheese on French fries. So I used a flat-tip screwdriver to pry some of it out being careful not to damage the aluminum threads on the manifold. The piece that was still in there was a full circle. All I had to do is pull a small arc of that circle out where I could then pry the rest of that thing away from the threads while using a pair of needle-nose pliers to grab the pieces.

    I then use a circular wire brush, the size of a button, on a 90 degree electric drill and an inside pipe threader to clean out the threads. I then went down to the dealer where I found out that GM's replacement part for that outlet is made of STEEL (good thinking). What an idea, to make something that is exposed to extreme heat out of a material that won't melt. I purchased the outlet for six bucks and the bypass hose for another four-something, and returned home. I installed the outlet, replaced the alternator and reconnected the battery cable, refilled the coolant, and fired it up. No leak, no problem. In my opinion, they're too many jerks out there with too many hair-brained way to do something different.

  • lbthedoglbthedog Member Posts: 198
    Seen many leaks from corroded "quick connects" made out of pot metal. Usually ten year old vehicles. Some galvanic action takes place. For the most part both the 60 degree and the 90 degree V-6 s have a decent track record. Alternators being a weak point but considering how much power is put out on 12 volts, things could be worse.
  • 0patience0patience Member Posts: 1,712
    mastermechanic, (brrrr, like someone grating their fingernails down a chalkboard)
    there is a TSB out on those engines for the failure you are talking about.
  • adc100adc100 Member Posts: 1,521
    My daughter owns this car now. The vehicle has 76K. I haven't seen the leak because the car is NC and I live in Pa. Where does the oil leak at?? (It is oil) I know this an open question but do these leaks proceed to failure very quickly??? Of course the vehicle also has developed alternator noise as well. These Corsicas-that I once thought were good cars are a total piece of GM junk.
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