What does the piston slap in a 5.4 sound like? The reason i ask is because I have a slight rattle sound after my engine is cranked and has run for about 5 min at about 1000 to 1200 rpm but after it is warmed up good it goes away. I just changed my oil from 5w30 to MC 5w20 syn blend with a MC filter. Its a 2000 f-150 with 106k on the clock. It doesnt realy sound like its coming from the top end, more like mid to bottom end and towards the rear of the engine. Its not a deep knock like a rod will make,just a rattling sound in that small RPM range, any higher and it goes away. should i switch it back to the 5w30?

 

Go get a mechanic's stethescope and listen to your engine from underneath, my 98 Expedition had a similar noise, drove nice and slowly the noise got louder. At first I thought/hoped that it was just a noisey lifter/follower. When I checked with the stethescope I could clearly hear it at the rear of the engine. I dropped the pan and started checking the rod bearings and found #7 bearing was spun, lucky me.

 

I havnt been able to pinoint the noise, the only thing i can tell is when i have the hood up, its not as pronounced but seems more to the pass side of the engine. It doesnt make the sound at idle, its only just above idle and only in a very small RPM range but goes completly away when fully warmed up.

 

I hate to say this, but that is about the same as mine was. I certainly hope that it is not that.

When you find out for sure, let us know.

 

Could be the the weight of the oil. Maybe too thick. Don't laugh.
I've been reading lots of info on these "modular" engines and have recently found data that states ford encouraging us to use even a THINNER oil than 5w30. Look this up on the internet and see what you find, you never know.
I believe it's the EXTREEMLY tight tolerances that require the thin oil.
I'll read more and see.

 

These mod motors need to have the thinner oil....5w30 or 5w20...they both have the same 5wt when cold. If it goes away once warmed up, then you should be fine. Usually bad rod bearings will make a sound all the time. What you are hearing is the "piston slap" due to the short skirt design of the piston's.
Rich

 

I know the sound of a bad rod or main bearing and even a spun bearing and this is not the noise im hearing, its too light of a tapping to be the bearings and yes it goes away when warmed up and no noise at all under acceleration. Just a note, I changed the oil back to a 5w30 ( thats whats on the sticker under the hood ) and it is less noticable than when i had the 5w20 in there. I think i will stick with the 5w30 and the MC filter.

 

My bet would be it is an exhaust leak at the manifold. I had the same thing happen on my expedition. Manifold had a broken stud. I installed a new gasket and no more noise.

 

I've been driving a 2002 F-150 supercrew/2wd for about 5 years now and what your describing fits my truck to the "T". I also have the 5.4 and this truck has never let me down . I't has made that sound sence I've owned it. It had 50K on It when I bought it , and now about 108K. I'm going with what "96f150" said (short skirt piston design) and hope she don't go down. When Its warm You can't even feel It idle and thats when The A/C is cranked in gear sitting at a lite in heavy traffic. I work and live in the SO. West and run a syn/blend 20/50 or 10/40 oil service all fluids when recomended . I use it for personal/ family stuff. I've had a lot of ford trucks (company owned) in the past , beat them up daily workin road construction and can't say I hated them all due to bad product design . So....uh... If you find out I need to start worrying give us all a shout,I will use that information. thanks!!