The 3.4 DOHC is a #$@ to work on. By the book, you're supposed to remove the rear head to replace the alternator. The 3.1 MPFI in my 91 Lumina was a beast, I totalled that car, rebuilt it, went hardcore mudding with it, ran it without oil, name all the bad things you can do and I did it to that motor, and I still had 240K when I junked it. 3100'* rarely blow head gaskets; I've personally never seen one blow and rarely hear of one that has blown. INTAKE gaskets, now that'* another story. Malibus seem to be worse than Luminas, I've done intakes on Malibus with 50K on them.

There is that exception; those that think an intake gasket is just another small leak and refuse to replace it and lose all their coolant, either into the oil or elsewhere. I miss my Lumina, that thing went through EVERYTHING. I'll have to post pics of some of the messes it'* been through (I had my digital camera with when I slid into a tree at 40mph head on -- it looks kinda funny, with the headlights popping out like a comic pair of eyeballs). The transmissions were fairly good as well, I got 200K out of my original one until I used it to pull my dad'* 97 C1500 out of a steep ditch. I didn't realize until after it was out (and after I had done a major burnout) that I was only spinning one wheel the entire time and burnt the transmission. Lost 3rd gear.

The 3400 is a good engine overall. They all at one time or another will experience an intake manifold gasket leak. But other than that they are pretty reliable, and as long as you don't run it hot you should have no problems. As soon as you overheat it a little you will blow head gaskets due to it being Iron block/aluminum heads. The heads will warp and obviously with a warped head you can never get the head gasket to seal. It is exactly the same engine as the 3100 except with a larger bore. Anyone that says the 3400 is worse than the 3100 is crazy because they are literally the exact same thing but with different bore sizes. That would be like saying a 350sbc is worse than a 305sbc.

You MUST be thinking of the 3.4L DOHC. The 3400 is an entirely different engine, its whats in the Malibus, Grand Ams, etc..... Pretty peppy for what it is and pretty reliable. Its essentially the engine I have in my STE with a larger bore size and no turbo.

Shawn

Very interesting stuff. So lets go over some new questions, if it does blow again, would it be best to go with an aftermarket gasket? And if so which brand?

You said head gaskets blow due to high heat. What if I replace the thermostat with a lower temp one?

And how hard is it to replace the intake manifold gasket on this engine?

Thanks for the info and I hope you can answer the rest of these questions, he really loves his minivan and he would hate to ether give it up or go through another head gasket replacement. If there is a better aftermarket gasket though I may convince him to keep it and just go with another replacement one more time.

1) I'm not sure what brand gasket he'* been using, but I wouldn't necessarily replace it with an aftermarket gasket so much as just a different brand gasket.

2) Changing the thermostat will have no effect on head gasket failure rate.
EDIT: Unless the current thermostat is stuck shut, of course.

3) As a professional automotive technician, a lower intake manifold gasket on a Malibu takes me around 4 hours to complete. But remember: I've done at least 50 of these -- I have air tools, lifts, everything in an auto shop to play with. There are some tricks you learn that makes the job much easier and faster. My first one probably took 7 or 8 hours.

If the head gasket blows again, I would say that it has a warped head or heads and that would need to be replaced before a new head gasket is going to do any good. As was already said, its usually a pretty safe bet to go with felpro or GM gaskets. (gm will likely cost more)

An intake manifold gasket isn't too difficult, I can do one on my car in a couple hours, but I've also had my engine apart a lot of times. I would say with normal hand tools it would probably take you 6-10hrs. (like was already said)

A lower temp thermostat isn't going to help much because if its overheating the thermostat isn't what is causing it (unless the t-stat is bad). Overheating enough to cause the head to warp is due to something else. A cooler thermostat wouldn't be a bad idea, but its not going to help this problem much. I usually just run a 160-180 t-stat in all my cars just as personal preference. That way if it does have a problem that causes it to overheat I have a little more time to catch it. (and in my turbo cars the chips require it)

Shawn

they did release a updated intake manifold gasket for the 3400'* (and other 60* v6'*) that when properly installed doesn't fail as much as the original.

the 3.4dohc was based off the quad 4, not the 3.1. the northstar also began its development around the same time, 2 quad fours sharing the same crank basically. it wasn't realesed untill 93 because they didn't have a transmission to hold it (fwd auto)