rmalone

So geico are you saying that because banks claims aluminum melts at approximately 1220deg, it is undeniable fact that all CTD pistons will melt if exposed 1300-1400deg? Just curious. Banks also claims that 1300deg sustained is no problem for any CTD.

And yes, when enough people observe the same anecdotal evididence I do start to listen. I do agree with you that if a person adds extra fuel to their engine they have no right to expect the dealer to cover a melted piston or blown turbo. But to claim that third gen trucks wont sustain 1300-1400 deg because the melting point of aluminum is 1220 seems funny, given all the different aluminum alloys available, and the anecdotal evidence that suggests (I didn't say proves) that the third gens in particular are capable of sustaining higher egts than 1st and 2nd gens.

I myself wouldn't consider sustaining anything higher than 1300deg. I will agree that running a truck at 1300deg will wear it out faster than running the same truck at 1000deg I just don't think it means imminent meltdown.

As far as it being foolish to exceed the design parameters of our trucks, I agree realative to the warranty and total miles the truck can go. However, that is the funnest part of owning these suckers.

Geico266

You do not understand the effects of EGT's on a moving piston. EGT's are Exhaust Gas Temps., not the saturation tempurature of metal (pistons)

The temperatures these guys are talking about are readings that PEGGED a 1,500F guage.

You need to pay attention!

PourinDiesel

So when I max out my EGT gauge @ 1700* sledpulling is this bad?

mikmaze

Name: Aluminum Symbol: Al Atomic Number: 13 Atomic Mass: 26.981539 amu Melting Point: 660.37 °C (933.52 K, 1220.666 °F)
That said, our pistons are not pure Aluminum but an alloy, creating a metal with a higher melting point. But dang do we push the limits or what well for the time of combustion and the mass of the piston with only the surface exposed I guess it is a good thing we have oil jets coling the bottom because the topside sure gets a beating.

Geico266

How much higher than 1,220F are we talking about?

mikmaze

ok, link me the alloy used in the piston and I will, I looked up the aluminum, can you find the alloy?

PourinDiesel

Geico,
Since you are the metallurgical expert on the forum can you give us the chemical formula or name of the Aluminum alloy used in the piston.
It would be a great help for this discussion for us less "in the know".

thanks

Geico266

It's pointless to name the material when no one understand the diesel & engineering theories behind it, but here goes.

The claim has been made that the aluminum alloy used in our pistons melts at a much higher temperature than stock aluminum. I didn't say it, (and I don't believe it) so why do I need to prove something I didn't say or don't believe?

The facts are the alumimun alloy used to make our pistons melts at 1,250 F. That is only 30 F higher than stock aluminum. (and you feel all warm and fuzzy with a 30 F increase in melting point?) But, at 1,220 F. the top of the piston is so soft it could not possible sustain the internal pressures of a diesel engine. IMHO. Hence a "blown" piston. The melting temperatures are with the piston out of the truck in a melting pot with a constant heat source.

This does not mean EGT's of 1250F will melt a piston. There is not as much heat in the EGT's transfered to the piston top. Its kinda like holding a torch to a metal bar. The flame is 2,000F+ , but it takes a long time for it to heat up and turn red (saturation temperature) This is the theory of heat transfer. The piston is being cooled by the cool air coming in on the next stroke, and its being cooled by engine oil from the underside shooting on it, carrying the heat away.

High EGT's also mean you are "coking" (cooking) the oil to a point where the volitals are flashed off leaving sludge, sticky rings, scored cylinder walls, ect., but that's another story.

There is a reason DC didn't want us to have all the power these engine can produce. The average "joe sixpack" cannot deal with understanding the complexities of running an engine "on the edge" of destruction. So they dummied them down so everyone can just get it and go.

By all means go out and have fun, but if you don't take the time to learn what it is you are doing to the engineering limitations of the materials involved your tuition to the school of "hard knocks" will get very expensive.

Sustained EGT's of 1250-1300F are okay. EGT's of 1500+ for a very short period of time are "okay", but its kinda like smoking cigs or laying in the sun. You might get away with it for awhile, but eventually it WILL kill you.

PourinDiesel

Maybe when my engine breaks down you could come over and work on it for me, since I obviously don't know what I am getting myself into.

Scotty

I have an early 04 and two injection events.

Mark at TST was telling me they have uncovered a fourth event that happens on the newer trucks when under hard load. He told me this at May Madness 04. I do not have any proof but the way he was describing it was pretty much how he tells anything and I see no reason for him to say something non factual. Over 30 yrs with Cummins might privy him to some good inside info.

Back to the melting pistons.

Special alloys are a lot different then good old plain aluminum.
There are also oiling nozzles that aim to cool the piston as well as the constant air flow. I agree that a long term hard pull at temps over 1300-1350 could easily heatsoak the pistons and distort their shape, skuff and then who knows what else.

I ran over 600 kilometers with a total weight of a high profile load of 33K pounds into the wind over steep grades and the egt hovered between 1250-1400 all the way. Most of the run was steady at 1250.
After cooling it down I decided to have a look at the turbo...clear coat was all nice and brown and peeling off. Whoops.
I do believe I was running on the ragged edge of max temps. I did break in the engine nice on that run.

Scotty

Superduty

Err... combustion temps at TDC are of the order of 2600-2800F, depending on a number of factors. Aluminum does melt at 1250-1400F, but the metal itself has to be at that temp. These are 4 stroke engines and the temp on the intake and compression stroke is much lower than on the power and exhaust stroke. Add oil cooling to the mix and the pistons don't melt.

Exhaust temps used to be indicative of engine loading. However, that doesn't really apply anymore when the 3rd injection event is thrown into the mix. Some people say that the exhaust manifold will crack before the pistons in a Cummins will fail.

BTW: EGTs on hard working naturally aspirated gasoline engines running at stoichiometric or leaner are 1600F.

TAS05CTD610

The theory is right about the pistons. Even if they were pure aluminum they won't melt due to the cooling of the piston from the bottom, sides, cylinder wall, ect.

A good example is the space shuttle (the ones that didn't burn up) Most are aluminum framed, copper wires that are covered with a rubber cover. The bottom of that sucker see's over (not sure what exactly the temp is) but problably over 10,000 degree's, but the shuttle dosn't melt..... Because the tiles disapate the head before it can go all the way through the tile. Same with a piston. While the top of the piston may get hot, you have the entire piston keeping the top cool.

Another good example is microwaving a frozen pot pie. The outside will be red hot and burning up, but the inside is still froze (sorry had to guys)

Getting it that hot isn't the best (as we all agree) but going up quickly and then back down won't hurt. It will wear things out faster, cause a more rapid wear on things. But the pistons will melt at a set temp, but the way the engine is set up the WHOLE piston dosn't get that hot, just the top.

RAPTOR01

I agree Mark is a great guy .. I stop a talk to him every chance I get or when he need some help .. now on injection events , the engine has 3 but you will never see them together . 1 pre 2 main 3 post .. the pre and main inject up to a set lower rpm witch you will hear the diffrent as you speed up , the main and post come in after that all the post is there for is to clean up smoke .So thats why you dont see all three injection at once . Chris

RamWheelsBy4

Ok now I feel like a "Chicken" because I have my TST EGT de-fuel set to 1600 and it kept getting there Friday night and screwing with my times. I was just too chicken to turn it off. Saw 1625 on the TST remote and my Autometer 1600* gauge buried a couple of times and just kind of backed everything off.

Maybe next time I will just turn it off and try not to watch the gauges or readout.

67Charger383HP

Great information in this thread!

I have no intention of getting any box for my truck, but after reading this, I do believe I will be checking into gauges.

Anybody seen that temp guide for transmissions that includes life expectancy at various temps? Is there one for diesels? Sure would like to see that.

I would imagine that life expectancy would be cut shorter than need be at a pegged EGT gauge for any length of time IMHO. But that only matters if you care to get lots of trouble free miles out of one of these like I hope to.