Recently, I was stopped in my 03 F-150 with 124,000 miles. All of the sudden one day, the engine started knocking. The knocking was coming from lower in the engine. After sitting for about two hours, I started it again. At first, no knocking, then intermittent knocking, then steady and after about 3 or 4 min, the knocking stops all together. Oil level has always been checked and it has never run low on oil. What on earth causes an intermittent knock?

I would strongly suggest that you not start this engine again until a qualified mechanic has figured out exactly what is causing a knock in the lower part of the engine. That is what I call an “expensive noise”, and continuing to run the engine is likely to make it more expensive.

Whether the cause is a failing oil pump, or main bearings with excessive wear, or a connecting rod that is about to part company with the crankshaft, or…whatever…that type of noise does not bode well for the continuing health of either the engine or your wallet.

Call a tow truck, and have it towed to a well-reputed independent mechanic for evaluation.

I was afraid of that. Damn…it’s been such a great truck.

A rod knock won’t go away after the engine warms up. I don’t know what would act like that.

The knock doesn’t fit easily in any common lower engine problem… Is there a change in the sound when shifted into gear? Maybe getting louder or softer. Does the oil look good? Has the truck been well maintained? And “knock” is a very relative term. Peck, tap, ping, knock, etc. The intermittent nature leads me to guess that it is a piston slap problem but don’t hold me to that. If you wish to investigate it yourself, first get a real oil pressure gauge and test the pressure cold and hot. And if you cut pieces of bare copper wire and insert one under each coil tower and attach a grounded wire to a screw driver shaft, touching the exposed wires will kill each cylinder and possibly indicate where the problem is.

I saw this same situation on a Ford tractor and it turned out to be a wrist pin. Using Rod Knox suggestion of grounding out each problem may help diagnose this problem.

If I had to pinpoint the sound, I would say it is back and lower engine. Oil changes every 5 to 7 thousand miles. Oil looks fine. It is a 5 speed manual transmission. And the sound will completly stop after running for
3-5 min. or when the engine starts to warm up. It is not a severe “knock”, but it is there. I will get an oil gauge and test oil pressure cold and hot. Also, not sure what you mean by coil tower. This truck has a coil pack, not individual coils for each cylinder. Is that what you meant by coil tower?