Ecoboost guys,

I found myself watching a YouTube video this weekend of the infamous start up rattle on the 3.5 engine. Further investigation on my behalf reveal that this is supposedly a well known issue. Also, quite a few videos out there of of guys doing the fix (new timing chain and phasers).

My question to you all is this: what EXACTLY is the source of the rattle sound? Which component is rubbing against what?

​​​​​​​Just curious. TIA

I was actually doing some more research on this just today. And what I found/realized is that the chain tensioner is activated or pressurized by engine oil pressure. So after the engine sits for a bit, oil pressure in the tensioner decreases thereby allowing the chain to slacken. So that explains the rattle only on start up - up until adequate oil pressure in the tensioner takes the slack out of the stretched links in the chain. It all makes much more sense to me now.

The chain/tensioner/phaser job looks fairly straight forward. Yeah, it's an all day job. But technically, not too bad. Recently did timing belt on Honda Pilot. This job doesn't look any more difficult than that.

Ford's design on the water pump on this engine definitely leaves something to be desired, though....