Exhaust Temperatures How hot is to hot

[MMeilicke]

When pulling 13,000 is is quite easy to reach exhaust temps up to 950 and still climbing with the probe mounted behind the turbo. How hot can the temps get before doing damage?

 

[SRadke]

The most common number you'll hear for sustained operatin is 1200-1250° pre turbo. Cummins says they test these engines up to 1400. Post turbo numbers are not as accurate due to heat loss in the turbocharger therefor they are rearely quoted.



-Scott

 

[y-knot]

True, they maybe not as accurate, but probably 80% of all CTD owners have their probes mounted post turbo. Why? Because it was the easiest way to do it, most use the 90 degree neck as the mounting. Mounting the probe pre-turbo is easy, but requires several more steps then post turbo. Many are just not comfortable drilling and taping the exhaust manifold.

Generally most feel that the difference between pre and post turbo temperatures run 200 degrees. This is maybe a convenient number to use, but is no-way accurate. The difference depends on the truck, it's mods, the load and even the atmosphere. I have both pre and post gages, and the difference can be as little as 10-20 degrees and as much as 300 degrees. If I was to use a number that was both safe and realistic, I would hold the upper limits to 1200 pre and 1000 post.

 

[Sarge]

You didn't say what year your truck is, but the 2nd gens get into the red zone after 1250*, and the 3rd gens after 1450*. The 3rd gens have an oiler that sprays the underside of the piston for cooling.....

 

[Matt400]

Originally posted by Sarge

The 3rd gens have an oiler that sprays the underside of the piston for cooling.....

I am sure you mean the HO's & new 600's cuz the SO 3rd gens don't have that.

Just thought I would throw that in there in-case some poor SO owner thinks 1450 is all fine and dandy.

 

[CJ8Rockcrawler]

So an 04 305/555 has the oiler and *should* be okay to 1450*? I don't plan on running mine that hard or if I do, certainly not for any extended periods, just trying to make sure I understand. I have SOOOO much more to learn about my truck!

 

[Matt400]

Correct, the extra oil jet on the bottom was added to the HO's to help cooling and then carried over to the new 600. The 03 & 04 SO's don't have that extra oil bath.

 

[Bill Stockard]

All the Cummins B series engines in Dodge trucks have oil spray cooling on the bottom of the piston, but the '03 HO engines and later actually have an oil galley in the piston head for additional cooling. One of several reasons the B series engnes have an engine oil to coolant heat exhanger.



Also the piston is running in cylinder walls that are the same or a bit above temerpature of the coolant which is relatively cold compared to combustion heat.



Bill

 

[Matt400]

Hrmmm, I guess I misunderstood what Cummins said here about the oil spray.

 

[Bill Stockard]

“We use gallery-cooled pistons which receive an oil spray to for cooler temperature and longer life. ” (Quoting Cummins)



That’s right. Previous to the '03 HO engines, oil spray was directed at the bottom of the piston for cooling the piston head (no oil galley) vs. the oil galley in the in the piston head in the '03 HO and later engines. I have seen both pre-’03 HO pistons and the ’03 HO and later pistons. They are quite different.



"Oil Cooled Pistons" was one of our sales features we used for selling the benefits of the Cummins B series engine beginning in the late 80s.



Bill

 

[GDouglas]

Posted from another topic:



After thinking about all the posts in the past couple of months about EGT readings for the 3rd generation trucks, I wonder what the average tolerance for accuracy that most brands of EGT guages have. It seems that some guys are getting 1300 degrees with hardly a load at all and some guys empty like me can stay on a long grade at WOT to just see 1150-1200. The hottest that my SPA digital guage has ever read is 1170. I was pulling a 6000lb load WOT up a steep grade in 5th gear, and had to shift to 6th since I ran out of revs for my speed. I am still completley stock.



Anybody know what voltages vs. temperatures data for the thermocouples that come with our guages? Maybe we can check accuracy of our guages that way. It could be that most thermocouples are dead accurate, but our guages themselves may not.



Just some food for thought that may keep a few of us guys from pulling our hair out with those "high" readings.

 

[Wiredawg]

Pre/Post Turbo Differences; Gauge Temp Variances

Fellow Rammers:



I see about 250' temp difference between pre and post turbo temps running at speed. I have both pre and post turbo EGT probes and where I see the biggest differences in readings is under acceleration and during cool down. The pre-turbo probe climbs faster and reads temps more real-time. The post turbo probe has a delay under acceleration and at cool down.



There are pros and cons to both: I installed both so I could have the best of both world and they tend to verify the accuracy of each other. In other words, the two readings are consistent with readings pre and post turbo.



I'm a llittle conservative on running under heavy load at the rated temp of the Cummins. I use 1,200' on my 02 as my redline pre-turbo for heavy pulling. I use 1,300' on my 03. I could probably go higher and faster, but giving a little headroom gives me more peace of mind. My 5th wheel is 17K lbs and I need accurate EGT info climbing grades.



Now, running empty, I will peg 1,500' my 02 truck and 1,375 on my 03 for a short 10 to 15 seconds while passing or running another truck. The 03 doesn't generate as high of EGTs as my 02.



EGT gauge accuracy was dicussed at May Madness. Seems there's a lot of slop in this area. If I recall right, Mark Chappel briefed everone TST tests their gauges to ensure accuracy. others may do the same. You may want to ask before ordering.



I guess the safest way to ensure reading accurcy is to get both, especially if you tow heavy or race.



Wiredawg

 

[ACerf]

Temp

I have an SO and have experienced pretty low EGT even when pulling my 32' trailer. The highest I have seen so far in over a year of owning my truck, is 1150 and that lasted about 5 mins. I have spoken to many people who have the 325/600 and there EGT's are much higher than mine. Which would make sense!

 

[Matt400]

Originally posted by Bill Stockard

I have seen both pre-’03 HO pistons and the ’03 HO and later pistons. They are quite different

I see, thanks Bill for clarifying that. I didn't mean to steer anybody wrong I just misunderstood what Cummins said about the difference.