Is the plenum gasket on these magnum 5.9 engines guaranteed to fail? I've read quite a bit on the repairs. I think I may have the original gasket. I checked the bottom of the intake with a magnet and it stuck so I'm sure it's a metal plate and not the aluminum aftermarket plates. I didn't get any oil from straight below but couldn't reach towards the back of the plenum. Been chasing a cylinder misfire that pops up random. Mostly been cylinder 8 for a while and now 4 has been pretty common on every run cycle after I clear it. Not sure if previous owners had the gasket replaced at the dealer.

 

Yep. Standard failure. You don't have to replace the steel plate with the aluminum feller though, just use GOOD quality gaskets, and get shorter bolts for the plenum plate.

 

I have about 82k and no signs of the plenum leaking that I can tell. I plugged the pcv valve and the hose that goes to intake and started up and removed the tube that goes from the filter housing to the other valve cover. I didn't get any vacuum from the hose I disconnected from the filter housing so it seems the gasket is good. I have no idea if the gasket was done previously. All I can see is that I see some black RTV type gasket on the front and back of the plenum. The sides look like regular gaskets. I like doing preventative maintenance but if I can avoid this one, I'd be happy.

 

Take a peek into the back of the intake, pull the throttle body if you have to. If you don't see oil pooling in there, (there will likely be a bit when the PCV gases enter the intake) then don't worry about. Just keep it in mind.

 

Just did the plenum repair on my '03 2500 Ram van with the 5.2l. Has 176,000 miles,was having a random "miss" at low to mid RPM's,with no codes thrown.Van would idle and accelerate perfectly in park or neutral,miss would occur only under load,and would not happen at higher rpm's.In the past I've replaced both cam and crank sensors,both O2 sensors,and had my PCM repaired.My plenum gasket wasn't blown,there was baked on oil from PCV on plenum plate.After the repair,the miss was worse,and finally got the multiple cylinder misfire code,as well as misfire in cyl #1 & #6.Pulled the wires for both to check the plugs and the metal tip of the wire stayed on plugs 1 & 6.looked like they had not been making proper contact for awhile.New set off wires and my van now runs like new.I'm not a novice,but this got me HUGE eyerolls from my father and brother for not following basic troubleshooting protocol!I'm glad i did it,it was easier to replace the valve cover gaskets with the intake removed,and the intake bolts were rusty,intake gaskets around the water ports looked a little sketchy.

 

I bought the aluminum plate/bolts from ebay,and used the Dorman gasket kit from Amazon,much cheaper than the Hughes kit.Gasket were decent,didn't use the t-stat because I recently replaced the water pump,t-stat,fan clutch,and radiator.

 

probed a camera down the intake. The complete plenum looks really clean but there is a decent amount of oil back in 1 corner. I'm not sure if this is normal oil from the pcv valve. Anyone have any input.

 

Use your camera to look at the gasket area where the steel plate meets the aluminum manifold, might be able to see if the gasket is out of place.

That isn't a lot of oil....... but, still not a promising sign.

 

haha. I'll take a better look tomorrow. Saw I can change the resolution on the camera as well. I'm still hoping for the best

 

Just plug the breather hose and then the PCV valve and hose. After that start the engine, pull out the dipstick and connect a vacuum gauge to it. If the plenum gasket is leaking you'll get a vacuum reading. If however it's starts showing pressure then remove the gauge and turn the engine off. Pressure on the gauge is due to ring blow-by along with a lack of vacuum in the crankcase.