Engine/Transmission (1998.5 - 2002) Explain this to me...(exhaust manifold question)

[steved]

Ok, this started a few weeks ago... found a couple small cracks on the top of my dad's 99 2500's exhaust manifold... they were about an inch long, no signs of leaking but I figured we had better get him another one because he was probably on borrowed time.



Thanks go out to Ronnie from Tennessee for selling me a perfect used manifold... it was a match and worked great, thanks again Ronnie!!



Well, we buy the gaskets ($17 EACH!!!!) and the turbo-to-exhaust manifold gasket... tear into it this past weekend. After removing the old mainfold, we flip it over... the manifold is about 1. 5 inches from being cracked into two pieces!!!!! The crack runs from the mating surface in the bottom and wraps almost the entire way around to the top... it had just started making the curve to the top (so it didn't look that bad). It definately showed signs that it had leaked.



Replaced the manifold with the new one... start the truck... it no longer blows blue smoke?? It would start and puff blue smoke all the time before... I figured since he was stating it was lacking in power that it was the CTD "getting tired" with 220k. Now, the turbo actually sounds like it is working, no more smoke, power is back to norm... awesome... good for another 220k!!!!!



Any ideas why it would have caused the truck to smoke blue... now I'm talking "oil" blue smoke and a lot of it????? It no smokie anymore... and the only thing we did was swap exhaust manifolds...



steved

 

[Doubleclutch]

Wonder what an egt would say. Any soot on the bottom side manifold crack? The metal used on the 12v manifolds shrinks with extra fuel, and 24v cracks. Don't be surprised to redo your efforts before another 220K But then again, your dad will probably hoark your truck before that happens...

My guess is that with the loss of power, extra hoof was on the throttle to get the old girl moving. Extra fuel and lower boost would give a black smoke, but not efficient burning... what does the crankcase oil smell like? Diluted oil might past the rings at 220K. That's my best guess.

Greg

 

[steved]

Wonder what an egt would say. Any soot on the bottom side manifold crack? The metal used on the 12v manifolds shrinks with extra fuel, and 24v cracks. Don't be surprised to redo your efforts before another 220K But then again, your dad will probably hoark your truck before that happens...

My guess is that with the loss of power, extra hoof was on the throttle to get the old girl moving. Extra fuel and lower boost would give a black smoke, but not efficient burning... what does the crankcase oil smell like? Diluted oil might past the rings at 220K. That's my best guess.

Greg

Yes, the crack had soot on it... how I could tell it had leaked. It also had a white residue along the edges of the crack as well as the black soot.



I know the 24-valve manifolds had cracking issues, I wasn't surprised when we discovered them on his truck... wasn't expecting the manifold to be ready to almost fall in half though!! As for selling the truck, after seeing how much $$ in repairs I have done to my 04. 5, he will most likely keep it till it dies. He has spent less in repairs in the last 7 year/220k than I have spent in 1. 5 years and 55k. I should have kept my 99! So, yes, we most likely will be putting another one on it another 7 years or 220k!



And the smoke wasn't black... it was blue like from burning oil. And it was most noticeable at an idle. Oil is still clear (changed about 2k ago), truck doesn't use any oil between changes... it actually leaks more than it burns... if it was from leaking rings, changing the manifold should not have affected that should it??



steved

 

[Doubleclutch]

Blue smoke at idle is what I missed, and I'm digging a long way back here. When you break-in a set of rings, you go to full throttle, hold it, back off, and repeat that cycle a couple of times... I believe the full throttle maximizes the pressure on the rings expanding out on the cylinders to increase wear and break-in of the rings. With an older engine, the break-in is... established. The rings are well worn. Leak-by is occuring because less pressure is exerted to expand the rings at idle, than at power allowing the combustion gasses to pressurize the crankcase= blow-by and blue oil smoke at idle, but not when towing.

Now back to YOUR truck... since we have the same truck... I had an injector stick on me, and have read of another poor soul who toasted his engine with a stuck injector (flushed a cylinder). THATS where I was coming from initially. Without pirating the thread, could you give the Readers Digest Condensed Version of what happened to your truck?

Greg

 

[steved]

Well, I thought about this some more... tell me if this makes sense:



You have a setup that makes so much boost (even at an idle). The computer is programmed to inject so much fuel at any given RPM... there isn't a sensor telling it that it is actually running "rich".



Now, if you lose even a little boost at idle, you are losing air getting crammed into the cylinder. If you lose the air, but keep the same amount of fuel, you essentially have a rich air-fuel mixture which the computer isn't designed to compensate for... resulting in unburnt fuel exiting the system at an idle causing the blue smoke... if this was a gasser, the engine would have loaded up and flooded itself... being a diesel, that won't happen since excess fuel is simply barfed out the tailpipe as "bluish" smoke.



That makes the most sense to me anyhow...



steved

 

[Hahn007]

Well, I thought about this some more... tell me if this makes sense:



You have a setup that makes so much boost (even at an idle). The computer is programmed to inject so much fuel at any given RPM... there isn't a sensor telling it that it is actually running "rich".



Now, if you lose even a little boost at idle, you are losing air getting crammed into the cylinder. If you lose the air, but keep the same amount of fuel, you essentially have a rich air-fuel mixture which the computer isn't designed to compensate for... resulting in unburnt fuel exiting the system at an idle causing the blue smoke... if this was a gasser, the engine would have loaded up and flooded itself... being a diesel, that won't happen since excess fuel is simply barfed out the tailpipe as "bluish" smoke.



That makes the most sense to me anyhow...



steved

I believe unburnt fuel would smoke black. Blue smoke would be lube oil. Your truck smokes black when you stand on the throttle until boost builds, this is excess/unburnt fuel. The only places I can think of lube oil getting into the cylinders would be the piston rings, valve guides, and turbo bearings.

 

[steved]

I agree, EXCESSIVE unburnt fuel is black... but, a little might look bluish... diesel is nothing more than a really light oil right?



AND, if it was rings, valve guides, etc... why did it quit when the manifold was changed? All those things are permanent wear items of which none were touched during the manifold swap... swapping a manifold wouldn't cause rings to quit passing oil, or leaking turbo seals to seal... know what I mean???



It is something really stupid most likely... and has a really stupid answer... .



steved

 

[Hahn007]

I agree, EXCESSIVE unburnt fuel is black... but, a little might look bluish... diesel is nothing more than a really light oil right?



AND, if it was rings, valve guides, etc... why did it quit when the manifold was changed? All those things are permanent wear items of which none were touched during the manifold swap... swapping a manifold wouldn't cause rings to quit passing oil, or leaking turbo seals to seal... know what I mean???



It is something really stupid most likely... and has a really stupid answer... .



steved

Not necessarily, with a major exhaust leak pressure inside of the turbo exhaust housing would decrease allowing lube oil to pass through a worn bearing. With the exhaust leak fixed pressure would be restored and wouldn't allow the oil to pass through the turbo shaft bearing. I agree with you about the rings and valve guides. I was pointing out those are the only places I could think of that would pass oil in general not necessarily in this particular instance. Sorry for the confusion I should have been more specific.





Chris Hahn