Engine/Transmission (1998.5 - 2002) what kind of knock is it?

[RBlair]

Not knowing much about diesel trucks this being my first, I don't know if it is normal or not. I hear it when cruising along on the interstate about 70, if I get on it, it gets louder and when I let off it goes away (at least I can't hear it). It does not seem to be temp related, and has been doing it since I bought the truck but I am beginning to wonder about it. It does not use any oil that I can tell. It had a Mopar filter on it when I bought it, and I have only used Fleetgurad filters the 2 times I've changed it. Used Rotella 15w40 in it both times.



The truck now has 78,000 on it, had 68,000 when I bought it used. Fuel pressure is still good, mileage had dropped a little but I figured it was the winter blend. Oil pressure about where it always is at around 75-80.



Is it nomal or should I take her in?



thanks, Roy



[edit] forgot to say that I searched the archives and found several instances of "knock" variations but none that sounded like mine, most were heard at idle as well as speed [/edit]

 

[RBlair]

I guess this is an indication that it must be normal.





Thanks

 

[B.G. Smith]

I think you are giving away your age. If you are mechanically inclined ang accustomed to driving gassers a few years ago, you always listened for knocks. Took me a while to get used to the knock of the Cummins, there is a sound that is very much like a loose rod in a 1949 Chevy. I suspect what you are hearing is the injection pump. bg

 

[drrhoades]

My truck has the same knock you are describing but it is a 97. The only thing I am wondering about is your oil pressure, mine normally runs around 40-45 all of the time. It might be different on the 24vs. Also when I increased my timing the knock got louder.



Doug

 

[ROADWARRIOR]

I think your oil pressure is too high for an engine that is up to temp. Mine runs about 40 to 45 at speed when warmed up. Could just be the gage. Also, winter blend fuel makes my 24valve sound harsher than #2. I don't remember it being that noticeable with my old 12 valve.



Dan

 

[RBlair]

It could be that I am "hearing" things since this is my first Diesel. It doesn't have the behavior as a rod or main in a gasser, but it does sound just like it.



As for the oil pressure, more info may be helpful. When warmed up as idle it is right at teh 40 mark. When cruising 70 mph it is about halfway between the 40 and 110 so I'm guessing about 70. Is this another example of the false reading that the oil pressure guage is programmed to indicate?



I'll take it in to Cummins this weekend and see what they think and post back.





Thanks

 

[PRout]

No its not a false reading.



I have had 2 isspro oil pressure gauges on my truck. The first one failed after about a year, so isspro replaced it. The good thing is I got to compare 2 gauges to the stock one. I found that the stock gauge is reasonably close to the isspros.



At normal operating temps, it cruises somewhere between 55-65 psi at freeway speed, and it idles at around 22-25 psi.



On cold starts it goes as high as 80 psi.



The lowest Ive seen it is 19-20 psi, on a hot day (about 117 degree air temps) at idle.



The highest was about 85, on a very cold start.



I noticed that oil pressure is very dependant on RPMs, and when the r's climb a little, the psi does by about the same percentage, except off idle where just a few revs off idle cause a big jump in psi.



Hope that helped.