I have already spent much time searching this forum for the answer... This is strange. I have an 02 Expy EB that has a rattling sound for about the first minute to 5 minutes of starting the truck. Not really a knocking sound. This just started out of nowhere. I know that piston slap is a common thing but his just doesnt sound like what I thought it would. At first I thought it was a bad idler pully or something. It has more of that type of rattling/sqeaky clanking sound then anything yet mainly heard from the passenger side of the engine. When you rev the engine you hear the noise on the down fall of the rpms. However, there is little to no sound just setting at idle. Other than that the expy runs great and drives fine. Its does use some oil though. About a quart or 2 through an oil change but, I do use Mobil sythetec which Ive heard issues about.

My lost of thoughts..haha

1. Could this be exhaust related
2. starter bendix -- however noise goes away after engine is hot
3. replaced PCV
4. coolant looks fine
5. exhuast is clean looking -- no smoke when started or running
6. probed all over with an electronic stethoscope -- cant really narrow it down. lowdest on passenger side of block closer to the head.
7. When hot you can turn the engine off for 2 minutes and it will make noise when started back up.
8. The noise actually goes away faster when the engine is started bone cold.

9. No codes are present
10. Gas milage is average

11. Maybe Im stupid and this is what piston slap sounds like...LOL

Oh ya.. The engine only has 44k on it as well.

 

Is it an exhaust heat shield? I'd get under it while it's cold, and bang around on stuff looking to find something loose. Piston slap isn't very loud, and it sounds like a really fast metronome. Does it sound like a tin trash can lid rolling down a stone driveway? Forgive me for the analogy. Rob

 

Ive beat around with a rubber hammer to check for that aswell.. I'll try it again though. Maybe with a bigger hammer..lol It sounds like something loose under the valve cover. Maybe a bit like trash can consistancy.

 

I hit around on the exhaust and everything is fine. There is a light sputtering hiss and light ticking from that side of the engine.. That part does sound like an exhaust leak at the manifold where it meets the exhaust. Could this cause a rattling/knock as well?

 

It's possible. Inspect the studs that hold the manifold to the head, you may have a broken one or two.
As it heats up and expands, the manifold reseals itself and the noise goes away.

 

Well crap! I think the problem has been found. I have a leaking manifold for sure. This morning when cold I started the engine then felt around the gasket areas. No leak there but I did notice on the back side of the manifold neck that air was puttering out. Now I have the decision whether or not to attempt this repair myself. I have everything I need but breaking studs is not something I want to mess with. Does this happen most the time or what? PB blaster hasent failed me yet..lol

 

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