Engine knock

BIGDAWG1962

MEMBER
2000 DODGE RAM
5.9L
V8
2WD
AUTOMATIC
193,000 MILES

Loaned truck to friend three days later he asked about oil type. Two days later I saw him and he said his mechanic said truck was good after he fixed it. I started truck and rods were knocking loud! I told him engine was on 7 cylinders and rods were knocking. Two days later he said truck didn't knock because it was fixed. Rods don't fix themselves. I think it is full of engine honey or masking agent. He had 1/2 gallon of oil leftover. Am I right about rods don't stop knocking by themselves?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

The cause of rod knock is a severe failure of the connecting rod bearing. Normally this is not going to get better which is why it tells me it was not a knock. Piston slap is the other noise that is described as a knock. This is caused by the piston and cylinder wall having too much clearance and again, it doesn't fix itself. Also, piston slap can happen if the wrist pin wears out.

Did you happen to raise the RPM and see if it got faster and louder?

Either way, if they put in the oil thickener, I suspect you have low oil pressure. It is rare but if you catch it as it is first happening and correct the issue, a rod can stop knocking as long as the bearing doesn't spin. Keep in mind, the is caused by no oil between the metal parts and that is what the knocking is.

So if you heard a knocking, there was metal to metal contact. However, if they just had low oil pressure and then corrected that, it may stop knocking if no bearing spun. The reason is, you are re-establishing oil pressure and it is now forcing the oil between the bearings.

If it is not knocking now then that is a good thing however, you will know when you change the oil if there is metal in it. So I would suggest changing it and looking for metal and how thick it is and then checking oil pressure.

Let me know if you have questions.

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