I plan on doing mine soon and still deciding if I should get an aluminum plate, now, speaking of different expansion rates, aluminum will expand about twice as much as steel for the same temperature change but we are talking about 100 degrees F or less and the difference in lenght for that range is very small. Now, the bolts that hold the plenum pan are still made out of steel and they also expand and contract less than the aluminum intake.

I have seen a series of very well done videos on youtube where the owner replaced the steel pan by aluminum and had the gasket blown soon because the bolts got loose somehow. Certain details like that could make a difference too. These videos are a great guideline IMO.


I think I'll do mine which is still original from factory at 60,000 miles re-using the OEM pan, black rtv on both sides of gasket and check on all bolts torque while taking it apart. Maybe I missed something but it seems that the same lenght OE bolts are used for the aluminum pan so they will not bottom up as they could if using the thinner OE steel pan.

I also heard from another owner who simply took the plenum off and just put in some thick washers and torqued all bolts again which solved his problem, the gasket was still in one piece.

It would be nice having some info on people who kept their OEM steel pan making sure the bolts are not too long.

 

Skip the RTV. The problem with that is, you can't lay a good even bead, that will spread nicely when you torque down the plenum pan. You will end up with high spots, and voids, that will leak. Best bet is just use a GOOD gasket, and shorter bolts, with blue lok-tite.

 

Thanks Hey You!

 

After loosing another O2 sensor, I have decided to replace the steel plenum plate with an aluminum one. I was lucky enough to grab a 2'x4'x1/4" piece of aluminum from an ex-employer, with their permission, of course. I traced out the pattern of the steel plenum plate onto the aluminum plate and used a jigsaw to cut it out. Then, I filed down the sharp edges caused by the cutting. I decided to leave one side of the aluminum plate straight. I don't think it will be an issue.
Since I have torn into my engine this far, I have decided to replace some things. Here is a list of the parts that will be replaced:
PCV (broke when removing hose)
Intake bolts (the TTY ones)
Intake gaskets (including plenum plate gasket)
Spark plugs
Wires
Cap and rotor
TB gasket
Harmonic Balance
Oil pressure sensor
Forward O2 sensor
Water temp sensor (broke when unplugged wire)
Timing kit (chain, sprockets, and gaskets)

I might have to replace the timing cover as well. It appears to have some cracks in it (I will post pictures) but I am researching to see if these are actually from the casting process.
All of these parts cost me about $250; the aluminum plate I got for free and I have priced a new timing cover at $182.00 -free shipping.
Is there anything that I have forgotten that I might want to replace while I have things opened up? Any input would be greatly appreciated.

 

Think your cracks are just from the casting process.

Don't forget the bypass hose from the water pump, to the intake as well.

Do yourself a favor, and get a good, double roller, timing set. The morse style chains tend to stretch too much.

 

Just did the plenum gasket over the weekend, took about ~13 hours total with cleanup. I mainly wanted to replace the manifold gasket due to an annoying leak down the bellhousing but did the plenum gasket as I was in there. I'll share a bit of my experience.

My stock plenum gasket was fine with no visible blowouts or leaks at 125k km's. The manifold gasket was blown out both front and rear and were leaking.

I've heard people say the stock plenum plan is "flimsy" or "cheap sheet metal" which really isn't true. It's approx. 12-13 gauge steel and is rigid. I had the intent of fabbing up an aluminum pan before this but after seeing the plate I have no regrets not making one. The expansion rate theory is debatable but I can't comment on it without any testing being done.

I used the Dorman kit 615310 with all the goodies and found the gaskets to be pretty good quality. It is an excellent budget kit. Only complaint is that I had to spend an hour today on lunch and $10 extra replacing the supposed 195 F thermostat included in the kit, which was actually a 160 F stamped incorrectly. Yes, I probably should've boil tested it before putting it in but hell I figure in this day and age they should be able to get a damn thermostat right.

The supplied plenum pan bolts were the same length as the factory ones and I had no noticeable issues with bottoming out when torquing. I used mostly Permatex anaerobic sealant for putting stuff back together. I used a thin coating on either side of the plenum gasket and in the corners of the manifold gasket.

If anyone is contemplating doing this job, it is not overly challenging just time consuming. Good idea to do the cap, rotor and distributor seal while you've got the intake off as well, looks like a royal PITA to do either of those with the intake on.

 

It's really only debatable for those who are bad at math. The dissimilar expansion rates are not sufficient to cause premature gasket failure when sufficient and consistent clamping force is applied via the bolts. For those who are bad at math and/or physics: If the dissimilar expansion rate theory had merit, there'd be puddles under factory original Ram and most other vehicles equipped with V-8 engines and automatic transmissions. Same aluminum, same steel, about the same surface area, about the same normal temperature excursions... no widespread leak problems except those created by clowns who won't use torque wrenches.

About the only improvement derived from swapping in the aluminum pan is due to its greater rigidity bringing greater equalization of the clamping force applied to the gasket. Whether or not it's truly a benefit I can't say -- it might be that a typical vehicle will require service that necessitates removing the intake manifold (and so acquiring an intake manifold gasket set) long before the plenum gasket fails.

 

Thermal expansion is not a theory. You can pull the coefficient of thermal expansion for aluminum/steel (basic metals) from any physics book...

 

Yep. Did that. Used one of my engineering reference books rather than a physics text. Aluminum expands about twice as much as steel... 12.3 versus 6.7 millionths of an inch, respectively, per degree Fahrenheit per inch. So over the length of the long side of the gasket, about 14" from center to center of the outboard bolts, and over the span from -30F to 200F (very cold start to normal operating temperature) the aluminum will expand by just shy of .040" and the steel by just shy of 0.019", for a relative motion seen by the gasket of just about 0.021" distributed along its length. That's not going to tear one ply toilet tissue.

I've not accounted for the expansion of the gasket material because I've no freaking clue what's in it. Chances are quite good that it's going to thermally expand a lot more than the metals around it and so be racing out ahead of the metal anyway. If it were going to be a problem, we'd all be spending as much time replacing gaskets as driving.

The failure is simply due to the tearing motion the gasket experiences. Where the gasket is sufficiently clamped it cannot move, where it is insufficiently clamped it does move (due to the pressure differential across it). At the point of greatest tearing stress the gasket will eventually fail. The deflections we see in the many photos of blown plenum gaskets are a helluva lot greater than tens of thousandths of an inch.

'Nuff sed?