I have a 2012 dodge ram 1500 5.7 hemi. I am getting a knocking noise from the engine on a cold start. The knock goes away after 30-45 seconds. Any ideas what might be going on?
How many miles?
In addition to the miles, how has it been used? Has it been towing a third-wheel horse trailer, or a flatbed with a backhoe on it, or never seen more than a bag of groceries? Do you plow with it?
Might the sound be an exhaust leak at the manifold? These trucks commonly suffer from broken exhaust manifold bolts.
Exhaust manifolds rarely “knock”. The noise is more of a tick or tap.
Knock usually indicates a rod bearing going away. A higher pitched kind of knock can be piston slap when cold but it usually happens on multiple cylinders so it isn’t a discrete sound. Like 8 drummers doing light rim-shots.
I too wondered about a rod bearing knock.
If you can, try having someone start it and rev it just a bit while you have your head under the hood. A rod bearing will become a sharp rapping sound. I like Mustang’s description of “rim shots” to describe the sound. In the case of a rod bearing it would be one drummer hitting rim shots.
Answer the other questions if you would. Very heavy use is a lot harder on engines, especially the bearings, than light use. Visualize it this way, wear to rod bearings originates as a shock wave to the rods when the combustion happens. Hauling large loads requires more power, ergo a lot bigger bangs. If the truck has lived a life of heavy use, the engine will be subject to premature wear.
Add to the questions the vehicle’s maintenance. If you’ve neglected oil changes, or allowed the engine to run low on oil, the bearings may have suffered.
Sorry for the delay in responding. Mostly city miles, but I trailer my Jeep every couple of months.
Oil changes are regular and it hasn’t run low on oil.
Are you sure it is coming from the engine? It happens while idling in the driveway right? If you’re not sure do some experiments, coasting in neutral, etc, to prove that it is the engine and not the transmission or rear driveline. There’s a known problem apparently with the differential pinion nut on this vehicle for example.
Other than that it seems like it is an engine bearing or piston problem of some kind.