Supposedly it does have zinc, but it's still less than what they had 20 years ago (or so I'm told by old people) and, you know, mo zinc is mo betta'

 

Months, years even. Do an experiment to determine what temperature it starts tapping at. My guess is it is around 190-200. Put in a low enough thermostat to always operate below that temp. I have 160's available, if you need to go lower just run without one.

 

I have a 175* tstat (actually in line ), but even with clutch fan i never hit more than 185*. Right now it's knocking at 175*. I guess i could try the 160, and see if it helps - i need to move the housing anyway b/c it's not clearing the efan. I'll order one when i order new gaskets (btw do i need one or two of the reusable silicone ones?)

 

So i did some more prodding and stethoscoping.

Loosening the accessory belt didn't change the knock (but funny enough couple other annoying noises went away, so i guess new pulleys are in order and looks like i will need to also inspect my alternator).
I manually turned on the e fan and dropped the temp (per OBD) to 160*(ish) - knock was still the same.

I did rev it up and kept it up at 2k rpm for a bit longer and actually i think the knock was getting fainter. I do need to check that oil pressure asap. Also looking at my wobbly balancer i can tell i get one knock per revolution, so that would eliminate valve train issues. My absolutely uneducated guess is that i got the slipped liner party or something loose on one of the con rods.

Not that it really matters but as for the location it seems to be the loudest at cylinder 7 (driver side closest to firewall). I had misfires on 4 and 6 when i got the truck. Leaky sparkplug thread on 2, but nothing ever on driver side... Always something new...

 

Hmmm, now I am suspecting low oil pressure. I have only seen one truck that the liners were slipping below 180 and it was an 04 (I did not buy it). Didn't you say you just refreshed the rod bearings? Oil pump gears ok?

 

I put in new main and rod bearings. I honestly can't remember if I ended up swapping the pump gears or not... I think the story was not to swap if they look fine b/c the OEM would still be better than any aftermarket stuff.

 

Yeah, true, as long as they were not cracked.

 

The drivers side is the one that tends to get slipped liners. There is a test involving running a hose over the block to cool it to see if that stops the knock. I was never able to get that to do anything for me. I had the knock for a couple of years and ultimately got the liners pinned. Best money i spent on this truck. I think I put it off as long as possible, it used to intermittent, tolerable. The day I dropped it off, it sounded like a freight train and you could hear it from blocks away. It is silent now.

 

I assume it knocks faster but does the sound lessen with more oil pressure? You can also get it up to temp and take off the serpentine belt, then run the engine for a couple seconds to see if the sound changes.

 

I think the knock lessen at high rpm, but then it can be knocking fast enough to just seem like it's gone. Taking off the belt doesn't change anything, at least at low rpm.