Phlegm noise in Overdrive

I've got a 5.2L with 158,000 miles on it.
Around 150,000 miles I started hearing a phlegm/knocking noise around 55 mph, or when going into overdrive or when releasing the pedal a little and then pressing down again. It's not a loud noise. It used to be very seldom that I'd hear it, but now I hear it anytime I'm on the freeway, or accelerating up a hill. It seems to just be getting worse. There is no loss of power or loss of performance. Any ideas?

have you noticed any oil usage?
I had a similar problem with my truck. at first it was only when the engine was under load(accelerating up hill, or taking off quickly, or when towing) at first I thought it was just a batch of bad gass, but the problem got progressivly worse. then I noticed that it had started using some oil(not much, like 1/2quart in 3000 mi.) turned out that what I was hearing was spark knock, and it was being caused by a blown plenum(belly pan) gasket. if you think that this might be your problem, there are a couple ways to check the gasket.....
1: remove the air hat, and open the throttle blades, and look down into the intake(flashlight helps) to see if there is any oil accumulation in the intake manifold.
2: with engine ideling and at operating temp, remove the PCV valve from the valve cover, place your hand over the PCV hole. if preasure builds, then the gasket is OK, but if you can feel vacume at the PCV hole, then the gasket is blown and should be replaced.
if it turns out that the plenum gasket is bad, if you are mechanically inclined, you can pick up a new gasket set and change it yourself in about 4-6 hours. if you have to take it to a dealership to be fixed, it will run around $400-$450 for them to do it.

I have noticed oil leakage, a little more than you mentioned though.
About 1/2 quart every 1500 miles. I will check to see if thats my problem.

That's pretty severe leakage.

that is some severe oil loss, and if it is in fact "oil usage" (oil being lost internally) and not leakage(oil actuailly leaking out of the engien and leaving a puddel on the ground) then I'd be willing to bet that your plenum gasket is in fact blown.
basically what happens is this: for some reason dodge uses a two piece intake manifold. the top part is aluminum, and the bottom is covered with a steel pan(AKA belly pan), with a gasket between the tow pieces. when this gasket fails, it allows oil to be drawn directly out of the crank case, and into the intake manifold and cylinders, thus causing the spark knock(pinging) and oil usage.

I haven't noticed any oil puddles under the truck, so I'm going to check and see if it's the plenum gasket. Any idea on what I'd need and how much time I'd need to change this gasket?

well, just the other day I saw a really good wright up with pictures on another site, but I can't seem to find it again.
anyway, you'll need to get a new gasket set(I don't remember the part number, but it will have plenum gasket, and intake manifold gaskets. 5 pieces total if I remember corrctly).
you'll basically be pulling the intake manifold, so you'll haveto drain some of the coolant, remove the AC compressor, alternator, and the bracket that those mount to. disconnect the fuel line from the fuel rail (may need a specail tool to unhook the quick connect). unhook the injector wires, throttle linkage, cruise cable, throttle valve cable(kick down cable) and any vacume lines that are attatched to the throttle body. I'm sure I have forgotten something, but once you have everything disconnected, pull the intake manifold. then just unbolt the pan from the bottom of the manifold, replace the gasket and reassemble everything.
you'll need a torque wrench, and a good manual comes in handy too.
I'll keep looking and see if I can find that wrightup that had the pictures and post a link for ya.
oh, and you'll also want to get a new T-stat, and gasket as you'll have to disconnect the radiator hose from the intake. it's a good time to switch to a 180* T-stat if you haven't already.
most shop manuals say that it should only take about 4 hours, but I alwayse like to give myself extra time just incase something comes up along the way.
the new gasket set should be around $35, but if you decide to take it to a dealership to have it changed, expect to pay around $450 to $500

Thanks for the info, I'm going to do it on Saturday, so I'll have plenty of time.

How often will I need to replace this plenum gasket? I started getting the pinging at around 150k. Will the replacement gasket last another 100K+ or will I be replacing it in another 5k miles. I read in another forum that a man had a dodge dealer replace his, and he had to have it replaced 5 more times in the same month.
Will I need to replace the spark plugs?
How do I get rid of the carbon that has built up? Do I just need a good combustion chamber cleaner?

well, I replaced my plenum gasket at around 60K, and am now at 85K with no problems. there are several companies that make billet plenum pans, that supposedly eliminate any chance of future gaskt blowouts, I'll see if I can find some info on them for ya.
also, I belive dodge has revised the gasket, and it is supposed to be better than the stock one.
or, there is alwayse the option of switching to the M1 intake manifold, which is all one piece, and eliminates the plenum pan all together.
as far as changing the plugs, I guess it depends on how long the gasket has been leeking. if the plenum gasket has been leeking for a wile, there is a good chance that the plugs have quite a bit of buildup on them, in that case, I'd recomend changing them.
as far as removing carbon buildup, you can pick up a can of combustion chamber cleener at the dealership, and I think it's prety reasonably priced.

I replaced the gasket this weekend, what a job! My check engine light is on though. How do I get it to turn off? Is this an indication that I did something wrong, or is it just because of having disconnected a lot of electrical wiring?
Also, I still hear the phlegm noise, Do I need to run fuel treatment through the system, or will it go away with time? If I replace the sparkplugs, will this take care of the spark knock?
I put a new 180* thermostat in but it seems to be running around 200*. Should it be running hotter than it did with the old thermostat, or colder?
I haven't had much time to test it out. I had to refill the coolant, which might have just taken a little time to get around the system to cool it down. I've only driven it about 5 miles since I did all of the work.
Thanks for all the help,

Did you make sure you added water with your coolant? It should be half coolant, and half water. Your check engine light is on probably because you don't have a connector back on good. Do a key code check and see what codes are coming up. That way, you can find out if it has to do with something you were working on.

Thanks, I'll do that. I did not add water, to the coolant yet. I was going to do that tonight. I just found a website with code check errors, so I'll check that tonight as well.

If you have 100% coolant in there, it will run hotter. Coolant is not as effective at disbursing heat as water is, which is why we don't runl 100% antifreeze. LTJG is right, 50/50 unless you're way north somewhere.

it would be a good idea to at least check the plugs, if the plenum gasket had been leaking for a wile, there is a good chance that some of the plugs may be fouled.
also, once you get the codes, all you have to do to reset the computer (check engine light) is disconnect the negative battery cable for a little bit, then hook it back up, and you should be good to go.

Alright, Thanks for all your help!

Well, I got home last night and checked my truck's "check engine" light. It didn't even come on. Thank goodness, there were no error codes.
I also poured water into the coolant. The temperature guage was real hot then real cold and real hot..etc. I drove it for about 15 miles, and it evened out right in the middle of 130 and 210. Then I shut her off. About 10 minutes later I started her up again, and the temp fluctuated again. Well, this morning I decided to drive the beast to work. The temperature never moved past half way between 130 and 210. It stayed put the whole way.
The spark knock only happened a little this morning, and I think it will go away after a few drives. My commute to work is about 60 miles, and I only heared the knock twice It was because I was trying to make it knock. It was much harder to make it knock this time, than before I fixed the plenum. I can't wait to see how it holds up, and if my oil consumption is taken care of.
Thanks to all for your help and suggestions.
Ya'll are going to laugh at this, but it took me 16 hours to replace that little gasket. The most frustrating part of the whole job was scraping off the old gasket from the plenum pan, and tightening up so many bolts 1-2 foot pounds at a time. I took my time, and made sure to do things right though. I've never done anything more than an oil, tires, or brakes change by myself. I learned alot about my 318 though, and really enjoyed the project. Next I have to replace my A/C. Any ideas where I could get a good compressor/clutch for a real good price?

Try eBaymotors.com. Sometimes you'll find stuff on there. If not there a local junk yard will probably have a dodge truck lying around somewhere. And then you could always pay top-dollar for one at an auto parts store or through mopar.