Ok, first I know that over the internet diagnosis is nearly impossible to be 100% sure on anything, but looking for some best guesses here.
a little background. I have owned my 1994 F150 4x4, XLT, 302, manual, long bed regular cap pickup since new. Has has only 1 oil change that went past 3000 miles. Have used nothing but Pennzoil 5w-30 conventional oil, and use WIX filters. Have never really beat on her, no serious offroading, use 4x4 mainly for snow and ice. Rarely pull anything or haul anything, and only a handful of times anything I would consider pushing weight rating of the truck. To put it short, I have always taken exceptional care of my baby even though Iowa winters and salt have taken their toll on the body. I love this truck. However, over the past 3-4 months, it has started making a slight knocking sound when first started cold. after a minute or two, it totally goes away and the engine runs quite as could be. No knock, no tick, nothing, sounds like a perfect engine. The oil pan was replaced a couple years ago.. I did not do this, a VERY reputable small town shop did this, the guys who own and run and work there are all mechanics that came from elsewhere and started their own shop. I had them do it due to that I simply did not have the time. Anyway, they guy who did the work, said with the pan off, the inside of the engine from what he could see was incredible, clean clean clean. He said the truck may die, but if it does it certainly wont be from that engine. He was amazed how clean it was. Ok, jumping ahead to today... like I said it has a knock, sounds like bottom end, and goes away, TOTALLY after she gets warmed up. Doesnt make the sound again until the engine completely cools down and is restarted. I changed the oil over the weekend, and after I was done, I was trying to pinpoint where the knock was coming from. Still cant seem to exactly pinpoint it, BUT, I crawled under the truck while running, and if I put my hand on the oil pan, and it seems passenger side, I can feel the knock on the side of the pan. I dont think so, but can the oil pump make a knock like this??? Only other thing that comes to mind would be piston slap... or a rod bearing. Wouldnt a bearing noise NOT go away? Piston slap makes sense, but I just find it hard to believe. When the pan was off, the cylinder walls still had all the factory cross hatching on them. Maybe its that I dont want to believe it. I have never experienced piston slap before so dont know exactly what it sounds like IF thats what it is. Truck uses no oil between oil changes, seems to run fine, just has this slight annoying knock upon startup. Any thoughts or guesses before I take her in to get checked out? As much as I love my truck, she does have 260,000 miles, well cared for miles, but a lot of miles none the less.

 

like you said, its hard to tell you what it is, find a video on you tube that sounds closest to your sound to give us a better idea. i would say you got a bad rod bearing but it normally wont go away after warmed up, it sounds more like valve problems.

 

Sure sounds like its coming from the bottom end though... and it does go away as soon as it warms up some, cant get it to make a sound no matter what I do once she is warmed up. Gut tells me its nothing serious to worry about, but mind tells me I havent heard this sound in the previous 17 years of ownership, "something" has changed. Dont think I will be driving her cross country right now LOL

 

yea my f150 had a top end tap, i put 10w40 in it and no sound since. i just looked at a 92 f150 yesterday with the 5.8l and it had a mild bottom end knock, but it was the entire time the truck was running. i know a rod knock is pretty loud usually. a valve tap cant be heard from inside the cab 95% of the time.

 

This isnt really very loud.. and I know that noise can sound like its one place, and be coming from somewhere totally different. havent tried using a stethoscope or anything yet, but I could definitely feel it on the right side of the oil pan, then as it warmed up it went away and I couldnt find it. I did put 10w30 in it this time, I believe the first time I have used anything but 5w30, didnt seem to make any difference. I have read about people putting oil treatments in and fixing their problem, but I am very hesitant about putting anything but oil in my crankcase. I have a feeling its either something that I dont really need to worry about, or something that I DO need to worry about and will be quite expensive. One or the other. and with my luck, it will be the expensive route.

 

try finding a vid of the sound so we got a better idea, since the noise goes away i would say not to worry about it, and maybe get a lil thicker oil or something. maybe oil isn't getting through the engine as much as it should on start up.

 

you have a common issue... main rattle....

What happens is simply this. when you shut the engine off the oils slowly drains back from the oil pump and pick up tube and galleries back to the oil pan... this is simply called drain back...

Oil filters have Anti-Drainback valves but in the last couple years unless you buy a 10.00 oil filter the drainback valves are made of cardboard and quickly fail....

chances are if you use either a Fram Racing or a bosch distance plus or K&N it would stop.... or you can buy a 100.00 anti-drainback check valve and install it.

main rattle is common on fords and has been since the inception of time... they have no bypass/anti-drainback in the block like Chevy's do....

you will notice it more now with added main and rod bearing wear... beings in the last 5 years they have totally taken all the ZDDP out of the oil it doesnt matter how often you change it the oil has NO lubricity... and if you havent been adding ZDDP on every oil change the bearing are wearing faster than normal...

the dry start ups is what kills them... the Zinc and phosphate in the oils is what help protect the bearings during a dry start up...

OR... buy an Accumulator and install it.....problem solved

The ONLY oil that currently has a fair amount of ZDDP in it is Brad Penn oils... formerly Kendal oil

 

Thanks for the info! Is there only one k&n? Gold? Whats best and where can I find? Worth a try.

 

I like the Bosch Distance plus... its like 14.00 and its worked well.. I dont have the main rattle when using it

 

Where can I buy?