We just bought a '97 Expedition with 140k miles on it. It seems to be in great shape mechanically with one possible exception: there is a strange noise coming from the engine compartment at highway speeds (70mph and higher.) It seems to be coming from the lower center portion of the engine compartment. The noise is sounds like a rattle or a rapid scraping. It only occurs at these high speeds; it does not happen at a certain engine RPM. There is no noticeable additional vibration when the noise occurs. It always goes away after slowing below 70-72 mph. I am thinking in terms of bad bearings somewhere. Any other ideas?

 

It's a piston skirt clearence issue. Most of them start to knock at 40k but I've seen some go as far as 100k before they start to knock. Ford claims that it doesn't affect longevity, I haven't seen very much to argue that. My 98 has 90k on it and it has been knocking since 50k with no problems.

 

If it is an engine noise it should be related to an RPM range not speed. It should make the sound at that RPM in the lower gears as the truck accelerates and shifts through the gears.

 

I have the same noise and I've been rebuilding engines for years. I have 114,000 on my '97 Expedition and have owned it for 6 years. For a piece of mind I went into the bottom of my engine. I found con rod and main bearings that looked like they were installed yesterday!! I found no wear in any of the places that I looked. I tried to move the pistons in the cylinder and they were nice and snug. I did find something strange. When i checked the clearance between the rods on the same journal they checked out but when I pushed them together they made that same noise that I've been hearing since 50,000 at startup. The con rod bearings were just barely as wide as the rod and the bearing edges weren't as rounded as I would have expected. the bearing edges help to maintain the rods location in relation to each other and the journal edges. It doesn't cause any problems but it seems like someone should look into it although good luck finding someone who has actually gone into the engine looking for it. There are a lot of people selling vehicles dirt cheap because of these noises and I'm telling you it's not a problem. Also Ford changed oil mid 98-99 from 10w30 to 5w20. The lighter oil does make the noise go away faster and run quieter. If this puts even 1 person at ease then I've succeded.
Hope this helps out!!

 

So you think it would be safe to go to 5w20 in my '96 Expedition, and that this might help with the problem?

 

Where on earth did you find a 96 Expedition? Thet didn't start making the Expedition until 97.

 

Oops. Yeah, it's a '97.

 

The head mechanic at one dealership asked why I wasn't running 5w20, which is what got me looking in the first place. I am running it right now in my '97 and it runs great. What JJLUVS2FLY said is right on! Excessive piston skirt clearance won't cause any problems untill it gets VERY excessive and then ring problems and oil consumption result. I'm an engine lover and if you listen to your engine, it WILL tell you that there is a problem. If you switch oils and your engine dosen't like it, It will tell you (More engine and valvetrain noise than normal) The one other thing that came up recently was that the expeditions have that filter relocator that mounts behind the fender, This has no check valve that I've seen and the distance from the pump means that it has to pressurize before oil gets to the engine which takes a few seconds. This can't be helping things either!!

 

I have a 99 Navigator which has developed a nasty rod slapping sound. Sounds like the problem above. It is just irratiating. I only comes up when, at idle, ran about 2000 rpms (up and down 100-200) and then goes away... It sounds like ....! I really hate to ignore it... The rig just turned 60k...

 

Just today I climbed under my '97 Expedition and was determined to find out for sure where this noise was coming from. I have 114,000 and I don't feel like buying a new one. With an engine stethescope I found that the noise was coming from the drivers side cat and resonator in the exhaust and not the engine. I checked all points of the engine and I didn't find any noise even though I could clearly hear it. I am positively sure it is coming from the exhaust and not the engine. I looked online and I found this quote and a suggestion for a fix and I quote" Ticking or knocking noise from exhaust. All 1997-2003 F-150s, as well as 1997-98 F-250s with the 5.4L V8, are prone to producing an irritating ticking or knocking sound from the exhaust. Ford describes the noise as similar to diesel engine operation, says it's most noticeable with the transmission in gear and the engine at idle and is due to normal engine pulses being amplified through the lightoff catalytic converters.

If your customer won't buy into the "normal" categorization, installing an exhaust wrap around each light-off converter should help quell the noise and satisfy him. You'll find the wraps as part of an Exhaust Shield Kit (Part No. 4L3Z-5E258-AC). Full installation instructions are included."
Please note that I found this noise BEFORE I found this posting and I was sure of it's location and now that I read this I'm sure that this is my problem and it might be worth looking into for the rest of you looking for answers.

 

O'rielly now sell pistons with a special piston skirt coating to eleminate the common knocking sound at vehicle specific rpms mine knocks @ 800-1100 and no where else i have pulled the oil pan only to find the bearings are still tight (plasitguage) and mains are good as well so i did some searching and sure enough pistons fixed it even though i bought SRP with a little dome 10:1 CR
no more knocking