Rod knocking
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I never use the car gage for diagnoses. They are little better than a dummy light. Even back when these cars where under warranty and they came in with "Low oil pressure" complaint it tended to be a gage problem not a engine problem. A jumping oil pressure gage is more likely a gage issue but if it is not I do not see it being an issue at that pressure. THe only thing those gages are good for is if you know what the pressure normally is. you then have a problem. over reved, over heated or ran low on oil. Then you see your gage is now reading low. That means you need to go get the oil pressure checked and get the oil check for metal flakes, chances are you hurt to motor but if there is metal flakes the motor is tearing itself a part.
Craby is right if it was just an oil pressure issue you would hear it in the valve train first. If the engine has too much bearing clearance then as pressure drops or oil thins due to heat then the lower end will get noise. This would not be the heavy knock of a hammer hitting the side of the engine. Just a light knock.
My old 2.8 (which was the engine the 3.4 came from) would drop below 10 PSI at low idle and that was when it make the knocking noise. I just enough pressure to keep the valves from clattering.
Just a heads up, there are two things that kill the GM V6 besides overheating (that is any car) Intake leaking coolant into the oil and stretching rod/rod bolts. If the rod bolt is stretched then all this becomes a waste of time and effort. The bolts can fail in slow motion. It will get a tiny bit worse every drive. If you can get the knocking to stop it may add some life to the motor but not much. You will spin a rod bearing.
Craby is right if it was just an oil pressure issue you would hear it in the valve train first. If the engine has too much bearing clearance then as pressure drops or oil thins due to heat then the lower end will get noise. This would not be the heavy knock of a hammer hitting the side of the engine. Just a light knock.
My old 2.8 (which was the engine the 3.4 came from) would drop below 10 PSI at low idle and that was when it make the knocking noise. I just enough pressure to keep the valves from clattering.
Just a heads up, there are two things that kill the GM V6 besides overheating (that is any car) Intake leaking coolant into the oil and stretching rod/rod bolts. If the rod bolt is stretched then all this becomes a waste of time and effort. The bolts can fail in slow motion. It will get a tiny bit worse every drive. If you can get the knocking to stop it may add some life to the motor but not much. You will spin a rod bearing.
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Newbie
Joined: Aug 2023
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Would that cause more than just two rods to be defective? When I took it apart only the bearings for cylinders 1&2 were slightly but obviously more worn than the rest
Thread Starter
|
Newbie
Joined: Aug 2023
Posts: 23
I never use the car gage for diagnoses. They are little better than a dummy light. Even back when these cars where under warranty and they came in with "Low oil pressure" complaint it tended to be a gage problem not a engine problem. A jumping oil pressure gage is more likely a gage issue but if it is not I do not see it being an issue at that pressure. THe only thing those gages are good for is if you know what the pressure normally is. you then have a problem. over reved, over heated or ran low on oil. Then you see your gage is now reading low. That means you need to go get the oil pressure checked and get the oil check for metal flakes, chances are you hurt to motor but if there is metal flakes the motor is tearing itself a part.
Craby is right if it was just an oil pressure issue you would hear it in the valve train first. If the engine has too much bearing clearance then as pressure drops or oil thins due to heat then the lower end will get noise. This would not be the heavy knock of a hammer hitting the side of the engine. Just a light knock.
My old 2.8 (which was the engine the 3.4 came from) would drop below 10 PSI at low idle and that was when it make the knocking noise. I just enough pressure to keep the valves from clattering.
Just a heads up, there are two things that kill the GM V6 besides overheating (that is any car) Intake leaking coolant into the oil and stretching rod/rod bolts. If the rod bolt is stretched then all this becomes a waste of time and effort. The bolts can fail in slow motion. It will get a tiny bit worse every drive. If you can get the knocking to stop it may add some life to the motor but not much. You will spin a rod bearing.
Craby is right if it was just an oil pressure issue you would hear it in the valve train first. If the engine has too much bearing clearance then as pressure drops or oil thins due to heat then the lower end will get noise. This would not be the heavy knock of a hammer hitting the side of the engine. Just a light knock.
My old 2.8 (which was the engine the 3.4 came from) would drop below 10 PSI at low idle and that was when it make the knocking noise. I just enough pressure to keep the valves from clattering.
Just a heads up, there are two things that kill the GM V6 besides overheating (that is any car) Intake leaking coolant into the oil and stretching rod/rod bolts. If the rod bolt is stretched then all this becomes a waste of time and effort. The bolts can fail in slow motion. It will get a tiny bit worse every drive. If you can get the knocking to stop it may add some life to the motor but not much. You will spin a rod bearing.
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A rule of thumb knocking at idle is rod or wrist pin issue. Main bearing normally knock under load like up a hill or acceleration. This is not absolute because sound traveling through a solid and mess with things. But the basic reasoning is, in order for a main bearing to knock you have to flex the crank as long as 2 bearings are still good. Rod bearings change direction every stroke, they want to knock.
Oil pressure jumping around would most likely be a sensor issue unless you have large metal flakes bouncing around in the oil passages. Before I pointed a finger at that I would want to confirm that with a hand held gage. Even a single flake of bearing material can get into a sensor and cause issues with it.
Did you save the old bearings? Could we get a picture?
For a quick test you could put some STP in your oil and see if it helps. I am not a fan of adding anything to the oil for long term use but if it helps then switch to the 20W50.
Oil pressure jumping around would most likely be a sensor issue unless you have large metal flakes bouncing around in the oil passages. Before I pointed a finger at that I would want to confirm that with a hand held gage. Even a single flake of bearing material can get into a sensor and cause issues with it.
Did you save the old bearings? Could we get a picture?
For a quick test you could put some STP in your oil and see if it helps. I am not a fan of adding anything to the oil for long term use but if it helps then switch to the 20W50.
Last edited by Gorn; Mar 19, 2024 at 05:53 AM.
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