Micaiahfied

ok, another thread brought this question up for me. i've always been told that the max safe EGT that you can run all day long is 1250*... then i decided to google the melting point of aluminum and cam up with 1220.666* can someone explain to me how this makes sence? thanks!

Cowboy_Customs

I dont think Id run 1250* all day long for sure. And I HIGHLY doubt ANYONE does. Being as your google search yielded 1220, I wouldnt top out over 1200 for just personal preference. You have to acctually get the ALUMINUM to 1220* first, then its all down hill. But what we are reading is the Exhaust air temp. Not the acctuall metal temp.

besides, I have gotten EGT's arounf the 1250 mark and that usually yields my water temp rising quickly to follow.

dieselJon

Plus I would think the pistons would be hotter than the Pyro no matter where it is (before turbo or after) My reasoning is because as soon as exists the chamber it starts to cool down. maybe not much but it could be enough.

Jon

wannadiesel

The pistons are oil cooled, that's why you can run hotter EGT than the melt point. Cummins says 1250, but how much do you trust your pyrometer?

Micaiahfied

that's the reason i was looking for dave. i don't push it to 1250 by any means, i was just wondering how the max safe was above the melting point of the pistons, lol.

1stGen545

The pistons are not pure aluminum. #2 Diesel requires 500* just to start. From the time it fires and ends the power stroke it is cooling from th peak temp even before it gets into the exhaust manifold. I know lots of guys ( including me) that hit 14-1600* regularly and on the oil analisis show no hint of a prob. Had the head off of my 92 about a year ago and it all looked fine with over 500K on it. I would be warryed about the turbo more than the pistons. Not saying you cant melt one I just dont think you should be afraid to get over 1200* at all like some guys on here. Just do what you feal safe with and go with it. Now that I said it I will prob melt one tomarow.

XLR8R

The pistons are an aluminum alloy, as most "aluminum" products are; although pure aluminum melts at just over 1200*F, the hypereutetic alloys - commonly used for internal combustion engine pistons - can easily surpass 1500*F before melting.

As posted earlier, the oil splashing under the pistons has a regenerative cooling effect which takes advantage of the alloy's excellent thermal conductance properties.

Also, the maximum temperature is not as important as the length of time the piston is exposed to elevated temps...

Due to the above factors, monitoring EGT only gives a general indication of the actual temperature of the piston crown, which is of course what's really important.

I think running EGTs in excess of 1200*F on any of the Cummins should be done with care.

p.s. .... having said that, I've run close to 1400*F for many minutes at a time while towing heavy, and gotten up between 1500-1600*F on numerous occasions during dyno & track testing.

1stGen545

Thats right. If its 1600* pre turbo the crown I think could peak over 2K* no prob. I could see it at 1200* at only 900* pre turbo. Like you said it is only a indication.