Engine/Transmission (1998.5 - 2002) Knock in fifth gear ! Problem Found

[Baja road Runner]

I have a '01 6 speed 3500 that had a very loud knock in 5th. gear at 24 to 26 hundred rpm's. After a long wait, Dodge Engineering replaced the thermostat for the third time with a new an improved unit. This apparently has solved the problem as the knock is completely gone under the same condition that made us think the engine was coming apart. They stated that this new design thermostat will possibly be a service bulletin for this type of complaint. Hope this helps someone with a similar problem.

 

[Rob Thomas]

Forgive my ignorance, but I don't see the connection between 5th gear, the "knock" and the t-stat. Please explain.



later, Rob

 

[Baja road Runner]

Neither did I. But for over three months and 6,000 miles, the knock was there under those conditions. The factory rep met with me and stated that under certain engine temperatures and rpm that the thermostat was causing cavitation in the cooling system with the affect similar to shutting off a faucet in the house and having the water hammer against the piping and the water jackets of the engine. All I know is that the noise is no longer present at any gear or power setting. Thank you for your reply.

 

[Rob Thomas]

Gotcha



later, Rob

 

[GAmes]

Cooling system cavitation?

Now you overvalved guys will have to start putting in PSD additive:{

 

[Extreme1]

Re: Cooling system cavitation?

Originally posted by GAmes

Now you overvalved guys will have to start putting in PSD additive:{

:-laf :-laf :-laf

 

[johnrv4]

Tell me more about the knock.

I know of a couple of '01's that are doing the same thing(including mine). I thought that it might be noises associated with the injection system(because my '98 12V was so much quieter). I think I might have the same problem. The noise is intermittent. Last time I pulled the TT, it was non-existent. But when it does appear, it sounds like a thumping engine knock.

 

[fj40charles]

Do you know what years are affected and what the part number is for the new thermostat?



Thanks,

Charles

 

[Texas Diesel]

Re: Cooling system cavitation?

Originally posted by GAmes

Now you overvalved guys will have to start putting in PSD additive:{

And then *you* woke up!!

 

[Waltz]

I have a 2001 6 speed that has had the knock that you are referring to in 4th and 5th gear when hauling my 12K 5er up steep grades since I bought it 2 years ago. Have taken it to dealer number of times and finally got DC engineer input. Relates that DC has known of problem for couple of years and, as you noted, its the thermostat causing cavitation in the cooling system. However DC will not change out my thermostat with the new design. Claims only 10 new thermostats have been authorized by DC to be installed as "test thermostats". Hard to believe. DC is now evaluating the results. DC may issue a TSB in future but I couldn't get a commitment. Also says there should not be any engine damage with the cavitation. Cavitation, eating into the cylinder walls of my ex Ford Powerstroke is one reason I got rid of that hunk of junk. How did you get the DC to authorize the thermostat replacement? Were you one of the 10 lucky guys to get it? Unless I can twist some arms appears I have to bid my time until the TSB is issued, if it ever is.

 

[Baja road Runner]

I do not know what years are affected by this problem as this is my first Dodge Cummins truck. I did have to wait quite a while for the revised thermostat and it was delivered to the dealer by a factory rep who was very knowledgeable about this and was very interested in knowing if this modified unit corrected the problem. I did contact them with the good news that it eliminated the problem. They did say that this unit was one of a small run to evauluate their use to eliminate the probelm. I have no part number at this time. I will contact the dealer and try to get this information. This modification also stablized the temperature gauge in a much narrower range. Will post any additional information I get.

 

[klenger]

Is this knocking sound the "sounds like a flat tire" noise when pulling grades in 5th gear (6 sp) with a load? Still waiting f r solution to that noise.



Ken

 

[Texas Diesel]

Originally posted by klenger

Is this knocking sound the "sounds like a flat tire" noise when pulling grades in 5th gear (6 sp) with a load? Still waiting f r solution to that noise.



Ken

Me too, I have stopped more than once to check the tires

 

[Baja road Runner]

No the knock is up front and sounds like a very hard ping or internal part of the engine that is not getting oil pressure

 

[Fireman Dave]

For me - it sounds like a dull rod knock. I also hear it at idle. I usually only hear it when I'm towing or have just gotten done towing. It eventually goes away. johnrv4 and I have compared notes on it before. Mine's an auto, by the way. It does run strong regardless of the noise. Hopefully this will solve it.

 

[Waltz]

For me the "noise" is similar to a "pat pat pat" sound, like the sound of the front tires running over a highway/freeway expansion joint/crack at a high rate of speed. Met with Service Manager other day and he relates that DC says the sound is truely coming from the heater core through resonation. He has heard that some guys have either pinched off the heater hoses or installed sections of tubes or pipes of a smaller diameter into the hose in order to reduce flow. Says this has eliminated the noise. I doubt it solves the cavitation issue as the cavitation is supposidly coming from the thermostat. Sounds as if the only solution is the new thermostat. Next time I hook up the 5er I plan to put vise grips on the heater hoses to pinch them off and see if the noise is reduced or eliminated when hauling.

 

[Goddard]

me too. thought i was nuts and just had not posted until i tryed to find what it was. sounds like a knock in the engine and only when on a hard pull (see sig)and usually towards the top of the grade. never thought it would be a thermostat causing cavitation.



i have heard water hammer at the plant in steam pipes and sounds like they are coming apart, never in a engine.

 

[claymike]

Well guys mine has been doing this for 2 years now. I have posted on this several times here. STAR told me a year ago that it was caused by the thermostat. The tech and I just laughed and shrugged it off as another one of their weird ideas. Well this morning on the way to work I noticed that my temp was up to 200 before it would open then it would bounce around between 185 and 200. So to make a long story short I searched on TDR and came across this thread and decided to change mine out with a new one. Well I guess what I am trying to say here is if you have the noise you better check your thermostat because when I took mine out the bottom was broke off. Luckily the washer was just sitting at the bottom of the housing. I may have had a little piece of the brass flange go into the engine. Just my . 02 worth



Mike

 

[JyRO]

Yipes!

I have been discussing this with Claymike for about a year now. Mine did it for the first time last September pulling a grade near Mt. Rushmore when I was in 4th gear (6 speed). Mine sounded like a tire going flat, and was a big worry on a 2500 pulling a 5'er, I couldn't stop where I was at. Narrow 2 lane going up a grade. I did let off and it went away (knew then it wasn't a tire). Got back on it, it came back. Let off again, and was going slow enough I had to downshift to 3rd, got back on it & it went away. It didn't effect power, and I couldn't feel a vibration anywhere.



I think maybe this sounds a little different to each of us because we're experiencing different levels of cavitation. But now I'm going to have to check my thermostat, to make sure mine's not broken, like Claymike's.



- JyRO

 

[Mingoglia]

For the price of a t-stat I would probably replace it just for the heck of it...