Just noticed something upon bringing the truck into the garage for misc look over and minor maintenance. Engine warm after a good drive around town, fully up to temperature. Not hot, normal. Turned off. Pop the hood. While the engine is cooling I can hear very distinctive POP, few minutes in between. The first couple are the loudest. Seems to be coming from the top side of the engine. I am wondering if this could be coming from the intake manifold and whether it is a known issue on the 4.7 as they age.
Absolutely, used to hearing minor ticks and creaks as exhaust system cools. This is something else. Much much louder and a "POP", like blowing and popping a lunch bag inside a plastic pail kind of sound.

The truck is a 2005 Dakota 4.7 auto 4wd. The truck is not run hard. Casual pleasantry drive about use. It runs smooth, it runs great, no performance issues.

Any ideas?

 

If it's around the top of the engine after a hot shut-down, it may be something heat-soak related (engine briefly gets warmer post-shutdown since the coolant stops flowing)...This was also the cause of vapor lock in pre-fuel injected engines.

One thing that comes to mind is that it may be a detonation of the fuel-air mixture trapped in whichever cylinder was in the compression stroke as the engine stopped turning, which was ignited by hot carbon buildup in the cylinder that got even hotter during this heat-soak after a few minutes...I don't know if that's actually possible, just speculating.

 

Heat soak is a good possibility. Thanks.
At this time I am suspecting it may be expansion/contraction movement of the plastic manifold eeeking against the bolts holding it down. I will have to check the bolts for tightness.


On a possibly related but slightly separate topic. The truck has had a really annoying tick on the drivers side for awhile. Saturday night I attacked that. I planned to expect broken manifold bolts. None broken. What I did find was:
- top rear bolt missing completely. The hole is stripped of most of the threads. Only about 4 threads left deep in the hole.
- the manifold is either warped or oem defect or bad design from the start. Lay the manifold on a flat table. 0.030" variance between front 3 ports but the rear most port had close to 0.110" air gap !!! The rear port on the drivers side also feeds the EGR, which the truck had previously tossed codes for.

I believe this manifold surface problem to be original and attempted to be fixed at least once before by previous owner. The manifold gasket gasket I took out was not in bad shape, not representative of the age of the truck, and the rearmost port gasket was sooted but not burnt or blown. This tells me the gap had been there all along, including the stripped bolt hole which is probably from the last guy trying to tighten it and get the gapping space to seal. No matter how hard you pull with the bolts, an aluminum head is not going to pull a heat cycled and hardened steel manifold flat.

Being a Saturday night, no machine shops, and truck needed in the am. My fix was pretty simple. I hand cut and layered pieces of gasket to fill in that rear port gap. The other gaps I did not concern with as I was putting in a nice new thick FelPro gasket which bridges them all. I bolted the manifold on and torqued all the good holes to 18 ft.lb. For the stripped hole, I used a non-manifold longer bolt that was able to bite into the last few threads left in there. Torqued that one to hand tight plus 3/4 turn.

Tick is gone, truck runs great, and noticed actual improvement in fuel economy to boot. Probably the effect of eliminating an exhaust leak and thus O2 ingress upstream of the O2 sensors. Anyways, l Will see how long that fix lasts. Crossing fingers. It may come back real soon or it may be years away. By the time it happens again I will have helicoil lined up for the one hole, and a machine shop identified to resurface the defective manifold.

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