Have you scoped it out with an automotive stethoscope? It might help you pinpoint the noise to a specific area of the engine.
" Oil flush? Why?" Because if my memory serves me correctly, and I’m getting old enough maybe not but I’ll bet you find the oil cap on this engine calls for 5w-20. Not 5w-30 or 10w-30. Engine probably has sludge built up not allowing good oil flow. The cheapest possible remedy= oil flush. Will it work? Maybe/ maybe not. It definitely wont if not tried.
Using 5w-30 instead of 5w-20 is NOT going to cause sludge. Extending oil changes or too much moisture however will. But I don’t think that’s happening here.
Second - if oil sludge is causing this problem then it sounds like it’s VERY VERY slugged up. Using an oil flush in this situation will probably do more harm then good. The sludge desolvers (Kerosine) will cause huge chunks of the sludge to come loose and block passage ways or even the oil pickup screen.
Don’t do an oil flush unless you know you actually have sludge and don’t do it if you have a LOT of sludge.
Thank you so far to everyone.
The manual calls for 5-30 in winter and 10-30 in the summer.
They did not yet move to 5-20 in 2004.
I am going to take a valve cover off to see if there is any top end sludge.
UPDATE… 6-20-12
Took off one valve cover.
Its very clean under there. No buildup at all.
I also let it idle for an hour after I put everything back together to get it nice and hot and revved it up every now and then.
Oil pressure stayed the same. It was running very smooth except for a bit of a tap when one of the cylinders fired. Just one though. Not a big deal.
Oil was still nice and clean like new afterwards too.
Let it sit for 10 minutes and then restarted it.
It still sounds the same when it starts.
I have the feeling that it very well could be the hydraulic timing chain tensioners.
It is just so loud though I am still having trouble believing that a loose chain could cause that much noise.
The timing chain will make a constant thrashing sound until the oil pressure pushes the tensioner in place and stops the chain from hitting the timing cover…This can make a lot of noise…When you had the valve cover off, you should have looked down inside the timing cover with a flashlight at the chain and it’s guides/tensioners…
Loose bearings will make a steady knocking sound for a few seconds…This knocking results in engine failure long before it gets very loud…
@Caddyman Thanks for the reply. You are right. I should have looked down at the timing chain but it slipped my mind. Its easy and cheap to take the valve cover off so maybe I’ll just do it again.
I will check that out.
Thanks for the info !