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Old 02-22-2010, 05:15 PM   #1
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Default Had the pleasure of repairing the infamous GM 3.1 and 3.4 lower intake? Come in...

I've got a 96' Buick Century with the GM 3100 in it, 94K miles on it. Changing the oil yesterday I noticed coolant leaking down both sides of the block. Thought great, there's no way both head gaskets went... So I checked out the seam around both heads, it was dry. So I looked around up top and noticed a big puddle of coolant under the upper intake manifold and it looked damp almost all the way around where the lower intake manifold mounts to the head. Did a little reasearch and apparently this is a VERY common occurance with both the 3.1 and 3.4 from GM from like 1994-2003... WTF?! almost a decade and GM doesn't do anything about it? From what I understand, the gasket material that they use isn't compatible with the Dexcool and deteriorates and cracks... nice...

Anyways, so before it starts getting into the crankcase (Doesn't appear to have done that yet by the looks of the oil) I want to get this fixed before I get to deal with internal engine damage from the antifreeze/oil mixture.

For those of you who have done it, need a little help. From what I understand, there is a revised gasket, I am going to use the Fel-Pro gasket as it's a metal/neoprene, which holds up just fine from what I have read. Also, I can re-use the old bolts just soak them with serviceable, breakaway loctite. Use black RTV on the edges of the valley cover as there is no gasket there... I was thinking about just using the GM assembly adhesive here, I don't really like RTV.

Other than that it's pretty straight forward. I turn wrenches for a living, so it shouldn't be too bad. Just looking for some heads up on odds and ends I'll need before I get into it...

Thanks guys!
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Old 02-22-2010, 05:26 PM   #2
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it's not as bad of a job as a lot of people make it out to be. one piece of advice is to make sure to keep track of the pushrods as they are different length from intake to exhaust. i cant remember right now which one is shorter. i just did this job on my wifes 99 Monte Carlo & it only took me about 3-4 hours & i was taking my time.
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Old 02-22-2010, 05:56 PM   #3
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FEL98004T is the small port intake set that is the good lower set. comes as a complete set with upper mani gasket and valve cover gaskets. leave the fuel injectors on the rail, just disconnect the fuel press reg. keep the pushrods in order. clean all the stuff out after you change the gaskets, meaning oil and coolant. it all gets messy.

do not reuse the old LIM bolts. they are TTY. check out here for the gaskets and such.
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in case you cannot tell, i do these ALOT. lol
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Old 02-22-2010, 06:03 PM   #4
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yes as john said do not reuse the lower bolts. just buy new ones they are inexpensive. the Felpro set is a very good set and seems to hold up the best. Make sure like everyone said to keep the pushrods in order or you will see some damage!. It is not a hard job especially if you work on cars for a living already! There is a really good DIY somewhere i remember seeing it a while back on a thread.
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Old 02-22-2010, 06:17 PM   #5
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id do it for $100 if you were in the area. lol.
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Old 02-22-2010, 06:57 PM   #6
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Cool guys, thanks for the heads up. Did you guys use RTV on the edges? I was thinking of using something like GM assembly adhesive instead?

I can get the new bolts from GM? I was told just to clean the existing ones and apply loctite. Apparently the new ones are just bolts with loctite anyways?
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Old 02-22-2010, 06:58 PM   #7
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Also, the car has 95k on it, anything else I should change out while I'm in there anyways? I was going to go ahead and do plugs/wires/belt, and swap out fuel pressure regulator because it's bad anyways...
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Old 02-22-2010, 11:44 PM   #8
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Quote:
Originally Posted by 98RedBird View Post
Cool guys, thanks for the heads up. Did you guys use RTV on the edges? I was thinking of using something like GM assembly adhesive instead?

I can get the new bolts from GM? I was told just to clean the existing ones and apply loctite. Apparently the new ones are just bolts with loctite anyways?
I would just stick with buying a metal gasket. Once a little air gets in with the Dexcool it turns to corrosive sludge. I would check all your coolant hoses and flush the system really well since you'll be going at it already.
Don't reuse the lower bolts as already said. The right way is cheap.
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Old 02-23-2010, 08:38 AM   #9
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Fel Pro has everything you need, including the new LIM bolts. Check out that site, its the one stop shop for all your 3100/3400 needs. You will have to use RTV on both the front and rear valley crossover. Buy a larger tube of it, as that small tube runs out. Do not use any sealant on the gasket or any surface other than the valley crossover. Make sure to clean off all the surfaces (including the tops of the heads where the valve cover gasket goes). Use a small dab of RTV there as well on that part where the LIM meets the head and has the notch for the valve cover. ALSO make 100% sure that the metal lower gaskets are seated perfectly in the holes on the heads and that they do not spring up. I have seen that happen, and when you go to tq down the LIM bolts, it will crack the LIM.

Just use some permatex RTV. The GM stuff is no better and it prob more $$$.

For spark plugs, just use some TR55s. No need for the expensive stuff or even platinum. They work just as well on the V6 engines as they do in the LS engines.
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Old 02-23-2010, 11:33 AM   #10
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A family member recently had this issue on his 01 Monte Carlo. I offered to fix it for $400 since it seemed fairly time consuming to move everything out of the way. They instead took it to a shop that charged $800.
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Old 02-23-2010, 11:35 AM   #11
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$700-1k is normal. It is not that big of a job but it does pay well.
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Old 02-23-2010, 12:00 PM   #12
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Originally Posted by John@Scoggin View Post
$700-1k is normal. It is not that big of a job but it does pay well.
Its good to hear he at least didn't get ripped off, per say. He wanted the job done over the weekend I had a wedding and didn't want to wait a week for me to take care of it.
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Old 02-23-2010, 12:45 PM   #13
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Quote:
Originally Posted by John@Scoggin View Post
Fel Pro has everything you need, including the new LIM bolts. Check out that site, its the one stop shop for all your 3100/3400 needs. You will have to use RTV on both the front and rear valley crossover. Buy a larger tube of it, as that small tube runs out. Do not use any sealant on the gasket or any surface other than the valley crossover. Make sure to clean off all the surfaces (including the tops of the heads where the valve cover gasket goes). Use a small dab of RTV there as well on that part where the LIM meets the head and has the notch for the valve cover. ALSO make 100% sure that the metal lower gaskets are seated perfectly in the holes on the heads and that they do not spring up. I have seen that happen, and when you go to tq down the LIM bolts, it will crack the LIM.

Just use some permatex RTV. The GM stuff is no better and it prob more $$$.

For spark plugs, just use some TR55s. No need for the expensive stuff or even platinum. They work just as well on the V6 engines as they do in the LS engines.
Awesome man, thanks for all the help!
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Old 02-24-2010, 01:40 PM   #14
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I've had two GM cars with 60* V6 motors, and have had this issue with both, twice with one. Not a terrible job, definitely take the oppertunity to do plugs and wires while you have the room to work and everything apart.

The other option would be to remove the entire engine, and reinstall a 3800 instead, perferably with an M90 on top - man a sleeper supercharged '96 Century would be nasty! They are nice and light too!
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Old 02-24-2010, 01:42 PM   #15
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If you have studied the architecture differences between the 60* Gm engines and the 90* Gm engines, you would not say that. Not to mention the large PITA to make everything work correctly. And there is no 3800 engine that is light. Cast iron block, Cast iron heads, Heavy crank, heavy cast pistons.....the math does not add up.
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Old 02-24-2010, 02:35 PM   #16
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If have studied the architecure of the fifth generation buick Century, you may not say that. That generation Buick Century was actually offered with a 90* 3300 motor until 1994, which shares the same external dimensions series I 3800 motors - much like the L99 and the LT1. So the architectural difference of the two motor's isn't an issue, the car was manufactured with either engine, and more specifically was originally designed for the 90* motors , and then the 60* motors were introduced and accomodated later in the generation, so the materials and potential needed to make such a swap certainly exists. The 3800 is absoutely a heavier motor, I'm referring to the car itself, those generation Centuries are pretty light cars - definitely lighter than the W-body car's the 3800 is usually in.

I abosultely agree with regards to plumbing and wiring you'd have a nightmare on your hands, I've seen 60* for 90* swaps in a few GM's, and its complicated for sure. My comment was largely in jest, I don't think it was hard to understand that doing a motor swap in place of a simple gasket replacment isn't a practical solution, and was offered as a funny idea that has some feasibility.
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Old 02-24-2010, 02:38 PM   #17
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I already knew that. I meant the potential for producing power. There is a reason that GM stopped making the 3800 but is still producing the 60*.

The engine swaps never work out like they are supposed to. I know most had alot of probs with harnesses/pcms. Even the people that are swapping the 4t65 in place of the 4t45 in the N bodies are having trouble that would not normally arise.
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Old 02-24-2010, 02:48 PM   #18
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Agreed. 3800 is really, really old technology. I bought a '98 GTP a few weeks ago, my buddy who used to have a 320hp a dohc twin turbo 3.0 VR4 was blown away that a motor displacing almost a liter more than his old ride made 80hp less on about the same amount of boost. I had to explain how all the old technology of the cast 2 valve heads, the ineffeciency of a blower over turbos, etc, etc could add up to such a difference. Strong as hell with all those old school "heavy" parts, absolutely. Potential for performance, definitely not.

Shoot, a perfect comparison show just how poor performing the 90* is to compare it with the new 60* dohc 3.6 - making more power than even the boosted 3800's, and returning much better mileage I'm sure. I'm no 3800 nut swinger, I just tossed it out there for fun. I do still like my (let face it, my wifes) new GTP - smooth, comfy, and tons of torque.
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Old 02-24-2010, 03:50 PM   #19
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They are nice. They needed a refresh. It didnt happen. The aftermarket is starting to weaken also, which kinda sucks for them. They needed an alum head.
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Old 02-24-2010, 04:01 PM   #20
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They are nice. They needed a refresh. It didnt happen. The aftermarket is starting to weaken also, which kinda sucks for them. They needed an alum head.
Better of them to build off the more compact 60* motor that already had the better designed aluminum heads - it has worked out pretty well, I liked my 60* motor's quite a bit, minus the gasket issues and the cold start rattle that just takes some getting used to. I wish GM had made a factory turbo'd 60* application, they take to boost pretty well - I used to have a Grand Am and be a part of that community. A couple of guys were making decent power with blowers and really good power with turbos on them pretty easily - just no trannies to hold it - and like you said that upgrade is no fun.
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