Rattle only at startup
06-04-2017, 10:53 PM
#1
Thread Starter
Join Date: Oct 2010
Location: Ohio
Posts: 42
Rattle only at startup
My 04 GT has 78k miles on it, has been given full synthetic 5w20 and motorcaft oil filter changes since it had low miles. Since I started commuting longer to take care of my Grandma within the past two years I've noticed the engine has a bad tapping rattle that occurs only at startup, kinda like the sound it makes on first startup after you change the oil and don't prefill the oil filter while it builds up pressure, once it's running it's smooth and quiet. It seems to get worse the longer I let it sit while I drive my other Mustang, but it doesn't do it every single time.
I was concerned it could be the plastic timing chain guides but I wasn't sure if they would cause a startup only noise or if they would make a noise all the time which it doesn't do. I don't believe it's an exhaust leak as it sounds pretty mechanical. I know the oil filter has an anti drain back valve so I'm not sure why it seems like it's starting dry when it sits for a while.
Any ideas?
I was concerned it could be the plastic timing chain guides but I wasn't sure if they would cause a startup only noise or if they would make a noise all the time which it doesn't do. I don't believe it's an exhaust leak as it sounds pretty mechanical. I know the oil filter has an anti drain back valve so I'm not sure why it seems like it's starting dry when it sits for a while.
Any ideas?
06-05-2017, 12:17 PM
#3
5th Gear Member
Join Date: Jul 2012
Location: ohio
Posts: 3,628
The chain tensioners are hydraulic, as the chain and guides wear the tensioners extend further out, it starts to take longer for them to pump up with oil pressure. Yes a broken chain guide can make the chain a little sloppy and cause a rattle when cold untill the tensioners get enough oil pressure in them to take up the slop. Its a common problem for the tensioners to start getting sluggish and start taking more time to pump up and also not hold pressure like they should. There is also a gasket that goeas behind the tensioner, they are known to blow out and lose oil pressure there.
06-05-2017, 01:42 PM
#4
4th Gear Member
Join Date: Nov 2009
Location: SoCal
Posts: 1,826
Purely as a band-aid to buy you some time you can try a "heavier" viscosity oil such as 10/30.
The SOHC 4.0 like I have in my Sport Trac suffers the same issue with worn guides and tensioners that don't pressurize as well as they used to on cold startup and result is that same rattle as your engine has. Switching from 5/30 to 10/30 on that engine has almost made the problem go away. Of course at some point an actual repair will be necessary, but on that particular engine you have to completely remove it from the vehicle because one of the chains is on the rear of the engine. On 4.6's the whole setup is in the front and as such is a much easier job to do.
The SOHC 4.0 like I have in my Sport Trac suffers the same issue with worn guides and tensioners that don't pressurize as well as they used to on cold startup and result is that same rattle as your engine has. Switching from 5/30 to 10/30 on that engine has almost made the problem go away. Of course at some point an actual repair will be necessary, but on that particular engine you have to completely remove it from the vehicle because one of the chains is on the rear of the engine. On 4.6's the whole setup is in the front and as such is a much easier job to do.