Knock in Fifth Gear

[Baja road Runner]

I have a 2001 3500 6 speed 4x4. It has 23000 miles on it. At about 19,000 miles whenever a grade requires the use of 5th. gear & about 75% power at 24 to 26 hundred rpm's the engine developes a very loud knock and the water temperature rises to 210-215 degrees. There is no loss of power. Took it to Dodge and there was nothing on the computer and they replaced the fan clutch and thermostat, this had no effect on the problem. I have spoke with numerous owners and diesel mechanics at Cummins to no avail. As we use this truck in Baja California a lot this is a major worry with 10% grades down there and no one to help if there is a major failure. I am a new member and this is my first Dodge. Thank you in advance for any help with this problem.

 

[C1B1DIESEL]

Can you feel the knock at all, in the steering, floorboards, shifter, seat, or just hear it.



Are you towing and if so what weight, and type, in the bed on the hitch or fifth wheel,



can you get the knock to go away, by going past the stated rpm or below it



do you have any mods on the engine. Injectors, boxes. do they change or make the knock go away by turning them off.



Is there any increase in exhaust smoke, black or dark hazing

 

[Baja road Runner]

Originally posted by C1B1DIESEL

Can you feel the knock at all, in the steering, floorboards, shifter, seat, or just hear it.



Are you towing and if so what weight, and type, in the bed on the hitch or fifth wheel,



can you get the knock to go away, by going past the stated rpm or below it



do you have any mods on the engine. Injectors, boxes. do they change or make the knock go away by turning them off.



Is there any increase in exhaust smoke, black or dark hazing

Thank You for the reply. We can't feel any knock at all, we have a 10'8" Arctic fox camper on the truck about 3400# . The knock will stop if I lower the power or shift to 6th and the temp will drop. The truck is bone stock. We have seen no smoke from the rear at all.

 

[StephenDelany]

Now that is a strange one...

I'm not an expert but it does not sound to me like you are having the engine come apart in front of you. One of the hot shots in this forum will probably be able to noodle this thing out. My guess is a bad spot in your injection timing that is causing something like pre-ignition in the cylinders. That would explain the knocking and the rising water temperature. If its hot in the cylinders another guess is that the fuel is being fully burned and hence no extra smoke. If that thing was getting ready to blow the "Jesus Pin" it wouldn't stop knocking as R's increased, you'd feel it through the firwall and the Oil Pressure would probably be doin' bad things in the guage cluster.

Good luck with her. .

 

[Pit Bull]

Did you check your lift pump pressure? With that RPM and load I wonder if a weak pump is causing the problem?

 

[claymike]

Several people have had this problem including myself. Mine does it in 4th gear at around 2400 rpm pulling a long hill. If I let up a little or take it above that RMP the noise goes away. Some have said that it is the air horn banging around on the air filter but that does not seem to be my problem. I have over 40k on the truck with over half of that towing a 12k 5er. Nothing has broke yet.



Mike