88 4.0 keeps blowing exhaust manifold gaskets

I got sick of listening to my old cracked exhaust manifold, so I paid a local shop with a good reputation to replace it. They charged an arm and a leg, but now I'm glad I paid someone else to do it because this is the second time the manifold gasket has blown in 3 months since they did the work.

Both times the same thing has happened: after a couple thousand miles or so, I start to hear a little exhaust leak under load. Then shortly thereafter it spits out a chunk of the manifold gasket from the very front of the #1 exhaust port. (Yes, I have a stud there and it is in fine shape.)

Anyone seen anything like this happen? What could be causing it? My only thoughts are: 1) poor torque, or 2) excessive exhaust backpressure.

it pretty common, i'd recomend searching threads. there was a good one I read not too long ago that talked about this. I think it was called "performance mopar manifold"

he put one in with a flex-pipe in between the manifold and downpipe which takes some of the stress off of it i guess.

oh and i've got an 89 w/ the same problem. your not alone ;0

Is it possibly that the exhaust manifold may be slighty warped? Allowing there to not be a tight fit between the head and the manifold flange?

The next time they put another gasket on have them coat each side with Permatex copper RTV.

1) Check the mating surfaces of the head and manifold for imperfections - if you can feel them, they're significant. Correct by draw filing (look it up if you need to - it's a useful thing to know...)

2) When you install the gasket next time, apply a thin (~1/16") even coat of RTV copper (nothing else - the red won't last...) to both sides of the gasket. Install gasket, install manifolds, install screws finger tight only. Go have a sammich and a cuppa - give it about a half-hour to start setting up. Maybe an hour. Come back, and torque to spec (start at top centre, clockwise spiral outwards, 19-21 pound-feet of torque.) Better to do to 10 pound-feet then to 19-21, since that will help the RTV "squidge" (technical term there!) into any remaning imperfections and such.

The RTV copper really is "copper-bearing silicone," and I use it on exhaust gaskets all the time. The Permatex stuff is also sensor-safe - I checked. The coating of RTV will give an extra boundary layer on both sides of the gasket, and will help to fill any imperfections that allow gasses to get past the "fire ring" (crimped metal ring around exhaust ports) that is likely causing your gasket to burn out.

Also:
Replace the screws and studs. I tend to use silicon bronze, but you can also replace with carbon steel if you can't find Si-bronze. Use SAE5 instead of SAE8 - and if you have to use carbon steel, replace them every time you do the job! They get weak with heat-cycling (although SAE5 holds up to repeated heat-cycling better than SAE8 does.) If you can get Si-bronze, then you can just anneal them and reuse them - heat them to a dull red (800* or so, I believe) and drop them in water. This reverses the "hardening" of the metal that takes place in use - and metal that is hardened without being tempered gets brittle (yes, I know it sounds backwards. Trust me - we're dealing with a copper-based alloy, and not an iron-based one. Copper responds to heating and quenching in the opposite manner as iron.)
If you put anything at all on the threads, use LocTite #272 or equivalent. No other grade of LocTite will survive the heat of "normal use," and you shouldn't need never-seez for this! (If by some chance you do decide to use never-seez, torque values are 5 pound-feet for intermediate and 10 pound-feet for final. But, you don't want that.) Why don't you want never-seez? Manifold screws work loose on their own, and don't need the help. If a manifold screw is loose enough long enough, you'll be doing the gasket job yet again! On that note, it's a good idea to check torque on those screws annually - you'll find one or two loose when you do. Don't skip the lower rear ones because they're a pain - those are usually the ones that are loose...
Make sure you retain and reuse the dish-shaped washers under the screw heads - they're there for a reason. That reason is to help keep the screws from loosening under normal use (iron expands .000006"/in/*F. Aluminum twice that. Screws that have to clamp aluminum and iron will have an uneven force under the head, that tends to unscrew the thing. The dish-shaped washers put a little "give" in the system to allow for this.) If you lose them, replace them - you can probably still get them OEM, or you can order Belleville Spring Washers from a fastener supply house. I'd probably use two under each screw head, nested together. I have yet to experiment with this idea, so I'm not sure.
If you need studs, you can cut them easily enough from threaded rod - 3/8"-16. Cut them about two inches long. Make sure to get new nuts - the OEM ones are threaded 3/8"-24 (there is a valid engineering reason for doing this sort of thing, but it doesn't apply here, as the loads are too small.) I use brass rod for new studs. Threaded rod in carbon steel is typically not treated to SAE8-equivalent strength, which is what you want. However, if you cut the studs from steel, coat the cut ends (since they won't be plated.)

If your still running the original CAT, it may be so plugged the pressure has to go somewhere.
Warped exhaust manifolds are common. I've had to file mine straight.
Make sure the manifold gets tightened from the center out.
Check your manifold and see if it glows red at night or the ends of your plugs look melted. I've seen some cooked gasket before, it isn't temperature proof, just temperature resistant.

http://catalog.remflex.com/category_s/85.htm

i wonder if this thick, carbon fiber gasket can be port matched to a renix head

its supposedly blowout proof.
I've got a leak at number 1 too, because the water jacket leaked around the stud, from head bolt 11. found this "super" gasket when I looked for a fix. Good for sealing up slightly warped manifolds, because it has a large amount of "crush", and is very resistant to heat.