: 2007 Engine Knock 4.6 Help

03-03-14, 10:10 AM
I noticed an engine knock one day and I cant diagnose it.

1. It does NOT knock when the motor is COLD.
2. Once it does warm up it does knock.
3. The knock only happens at idle and when RPMS are increased the knock disappears.

It had synthetic oem recommended oil in it and I changed it. (there were no chunks or metal in the oil)
I swithced to one size thicker synthetic hoping that might help and I am not sure if I am imagining it but I think the noise may have gotten slightly worse.

The motor has 160K miles on it.
Ive read piston, bearing, wristpin, clogged cat, piston slap could all cause some of these symptoms but none of them seem spot on for symptoms.... I dont have a video or an oil pressure checking device.

Any advice based on these 3 symptoms any simpler diagnostics i can perform to rule out possibilities.. Thanks I really appreciate the help

03-03-14, 11:00 AM
Are you SURE it's not external, like a belt tensioner or idler pulley bearing? A stethoscope would be a big help in narrowing it down.

03-03-14, 01:03 PM
Im not sure I guess but it sounds like an engine knock. I have had rod knock or bearing knock on a car in the past and it is the same sound only more faint from the bottom of the motor and with very weird symptoms like only when warm and only at idle...
How would I stethoscope it? do i have to go to a doctor supply store and buy a literal stethoscope like they use ?


I thought that the fact that its gone when under load ruled out rod knock?
I figures that was more an indicator of low oil pressure at idle but wouldnt it have even lower pressure when cold?
so im just super confused

03-03-14, 01:05 PM
Go to a NAPA and ask for a mechanic's stethoscope, or make one from a Walgreen purchase - remove the chest diaphragm and substitute a length of proper sized vacuum tubing from the Help! racks at any large parts store.

or Google "automotive mechanic stethoscope".

Unless the engine has excessive bearing (rod big end) clearance(s) to begin with, a slightly low oil pressure, warm, will not cause rod knock. Engine knocks are extremely difficult to diagnose sight unheard ..........

03-03-14, 02:03 PM
Give it a good drink of water?

03-03-14, 03:42 PM
Northstars have a very robust lower end. I would be very surprised if it where a rod knock.

03-07-14, 11:25 AM
Found an 01 dev with lower end noise for 1k/Bo.