Meh129,we've had some cool weather this week (20's at night, low 50's day) and guess what. Early in the morning, 25deg,I fire it up, no sound. No knocking,tapping,anything. My wife said "that's good" I say it makes no sense. I'm the type of person that wants to know "why". I've done nothing different, just driven as normal. This is gonna bug me for a while.

 

Well travlman, mine came back with the cold weather, so I went to another mechanic who works on race engines and before I could give him all the information he said it a was manifold exhaust leak. He even asked if it sounded like a baseball card in the spokes of a bike....so now I am going back to the place I had the work done and have them put on a new manifold gasket...I will keep you updated. Take Care

 

Meh, did you get the gasket replaced? If so did it fix the problem? I am having the same issues and the same problems with diagnosing the problem.

 

I took the last week in to the mechanic, they did this smoke test (seaform) through the vacum line. There was no smoke leaking from the exhaust and they said if the was a leak the smoke would come out. But we did let the engine get cold and took it out again and the noise came back they cant fiqure it out either. I am tempted to take the exhaust manifold off and see it for myself. Keep you posted.

 

IT'S BAAACK! About a week ago, with temps regurlarly in the 60's-70's and it's tapping again. Something else too, when the engine fires, the noise does NOT appear until the oil pressure comes up. That half second when the engine fires up, before the oil pressure builds, it's quiet. It's on the passenger side, back around the number 2or3 cylinder. Sounds like it's under the valve cover, but I've had that off, no broken springs or rocker's. That should confuse the experts out there.

 

Okay, quiet down, not everybody at once.

 

I have used the 5w20 synthetic since my truck was new. After 5 different mechanics looked at it, one recomened that run an engine flush with any engine flush additive, drain the oil, put 10w30 in it, drive it for 30 mles drain the oil and repeat 3 times. Yes that's right 3 oil changes in one weekend. This quieted the noise considerably. The theory is sludge building up in an around the lifters and inside the oil pan. The heavier weigh oil may have helped on its own. I am still running the same weight oil. The noise befoe was almost deafening if you were under the truck while it was started cold.

 

Mine only started when it was cold, and I thought that was the common factor. Apparently I was wrong. It's come back in the warm weather, and now it has faded again, to the point where it's almost not noticeable. Also, I have tried heavier oil, with no affect either way. I had considered a buildup in the valley, but there is no, and I mean no buildup whatsoever under the valvecover's, it looks brand new, with now 162,000 on the clock. I guess I'm down to either buildup near or on the lifter's, or a lifter that is about to fail.

 

I'm stumped on mine as well. I can tell it's coming from the underside of the engine though. I haven't ever had an engine torn down before but there is something on the other side of that darn oil pan making noise. If I stick my head down there at idle I can hear it. Tap Tap Tap with the RPM's. The darn thing only has 60k miles on it.

 

Mine is higher, almost near the top. If your's is that low, it may be a rod bearing. You can buy bearings for cheap, and change the offender yourself. You gotta identify which one, or at least which side it is, and just buy enough bearings to do one side. The Haynes manual SAYS that you can remove the oilpan w/the engine in place. I have read otherwise from some folks here though. If it is possible, you will at least have to remove the upper half of the intake manifold, and take the bolts out of the motor mounts, and jack up the engine to gain clearance.

 

So since I can hear the noise, even though it's quiet at idle, but at all RPM's you think it might be a rod bearing huh? Hmm... that doesn't sound like it makes for a fun weekend. Once you get the oil pan off how difficult is it to change the bearings? I'm pretty good with a wrench but I don't want to get in over my head. Keep in mind I have access to to an engine hoist.

 

It's possible, but I would get a mechanic you trust to listen to it, and give you his opinion. If you don't already have one buy a Haynes manual for about $12, and read up on bearing changes. If you are not comfortable, don't do it! Mine completely goes away some times, and then comes back for no apparent reason.

 

i sincerely believe that this problem is an exhaust leak. i have had the same problem for over a year. the multiple symptoms scream exhaust leak...and mine does not sound like an exhaust leak either. i suspect it may be a manifold problem with the passenger side manifolds.

 

I barely made it into my mechanic the morning I was going to have him look at it. My overheating problem and noise became soooo he could hear me coming from down the street. It overheated 4 times within one half mile. When I got there I had motor oil in my coolant. The problem turned out to be my intake manifold causing my engine to overheat. The overheating over time caused my lifters to warp in addition to sucking small amounts of coolant into my number 6 piston. The high preasure inside my cooling system caused small amounts of coolant squeeze out onto the piston and put a small hydro lock in that piston upon startup. When I would start it the next morning cold the noise was very loud, top end, but would then quiet down to about half of the defining volume. Me trying to diagnose the problem myself, taking the truck to 5 different reputable mechanics, including Ford (what a joke), spending about $600 in diagnostics fees and countless hours and sleepless nights of worry about the problem and getting up to "check one other thing" at 2am - I realized I was becoming obsessed. So that fateful morning when I died at the garage was almost a relief. After my mechanic took the top half of the motor off he called me down to have a look. There was my intake manifold gasket cracked and with a split about 2mm wide. If I would have taking the truck in and had the part replaced I would have saved my engine. I ended up replacing the entire motor with a new crate Ford motor with all Felpro gaskets. There is a class action lawsuite formed for the 3.8v8 with the same problem. If enought of us complaine we can get reimbursed for the damages.
My advise to all who read this that have similar problems and a 97-01 4.2L v6. Go and have the intake manifold replaced and save yourselfs $5,000!!!

 

I must apologize for my grammar and spelling in my above post. I was a little excited but I am very literate. And I didn't really die, my motor did...