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Old 10-11-2021, 07:50 AM   #1
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Safe EGT's

98 isb 5.9. I have been told that 1250 is the magic number to stay below. During summer I am riding 1250 all the way up a grade. I have to let off a little to keep it under 1250. When I say summer I mean approx 70 degrees outside. I always travel early. At 60 I can hold it to the floor and it only get to 1200 or so.
My question,
Is 1250 the threshold??
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Old 10-11-2021, 10:14 AM   #2
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Have to balance the placement of the sensor with Cummins temp recommendations .

Was there any guidance with the EGT installation instructions ?
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Old 10-11-2021, 08:06 PM   #3
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1250 is limited for continuous reading. Back off a little or down gear to keep in 1200 egt range.
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Old 10-12-2021, 10:51 AM   #4
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yeah, about 1200 continuous is the safe max. You would be measuring before the turbo (in the exhaust manifold).

My Coach has an EGT mounted just after the turbo and will run around 800 degrees under a heavy continuous load (so 300 to 350 degrees difference due to probe location).

https://official.bankspower.com/tech...-is-important/
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Old 10-13-2021, 05:37 AM   #5
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Quote:
Originally Posted by Skip426 View Post
Have to balance the placement of the sensor with Cummins temp recommendations .



Was there any guidance with the EGT installation instructions ?
I put the probe before the turbo..
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Old 10-13-2021, 05:41 AM   #6
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1250 is limited for continuous reading. Back off a little or down gear to keep in 1200 egt range.
When mine down shifts the Temps go up..
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Old 10-13-2021, 06:01 AM   #7
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yeah, about 1200 continuous is the safe max. You would be measuring before the turbo (in the exhaust manifold).

My Coach has an EGT mounted just after the turbo and will run around 800 degrees under a heavy continuous load (so 300 to 350 degrees difference due to probe location).

https://official.bankspower.com/tech...-is-important/
Nice read! Thx
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Old 10-13-2021, 06:09 PM   #8
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Why do my EGT's climb higher when it down shifts??
(Climbing a grade)
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Old 10-13-2021, 06:45 PM   #9
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Why do my EGT's climb higher when it down shifts??
(Climbing a grade)
more fuel, inhaled faster, but diesel is a slower burning fuel so more of the combustion heat can happen in the manifold as it finishes burning.

To lower EGT on a hardworking diesel engine, raise boost or lower fuel. A given amount of fuel SHOULD equal a given amount of work, running a diesel lean (more air but same fuel) should only have the effect of reducing the EGT as long as there is sufficient drive pressure to add more boost.

On my ISC, it would appear that I have insufficient drive pressure (or haven't really hit the smoke limit yet) b/c I seem incapable of getting the MAP to read higher than 22.5 psi on boost, while the wastegate is completely disconnected and that spring is so strong that I can't move it with a wrench. So with a power-adder chip turned all the way up, I *can* make it smoke a little, but the analog boost gauge still doesn't go above 20 (it seems to trail the electronic reading from my Scangauge-D) but the electronic only says 22.5 at WOT.

I'm still slowly investigating the potential of a boost leak elsewhere in the system, but I don't think it has one. I just think that's all the turbo can give. At 22+ psi, that is a LOT of air to move to stuff more in.

I'm not looking to lower EGT though, b/c flat ground at 70mph while towing a Jeep is about 800 degrees - right where it should be. Even climbing some grades it tops out at about 1100 degrees, that's all there is for heat. Pre-turbo, in the #6 port right now.
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Old 10-15-2021, 05:43 PM   #10
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more fuel, inhaled faster, but diesel is a slower burning fuel so more of the combustion heat can happen in the manifold as it finishes burning.



To lower EGT on a hardworking diesel engine, raise boost or lower fuel. A given amount of fuel SHOULD equal a given amount of work, running a diesel lean (more air but same fuel) should only have the effect of reducing the EGT as long as there is sufficient drive pressure to add more boost.



On my ISC, it would appear that I have insufficient drive pressure (or haven't really hit the smoke limit yet) b/c I seem incapable of getting the MAP to read higher than 22.5 psi on boost, while the wastegate is completely disconnected and that spring is so strong that I can't move it with a wrench. So with a power-adder chip turned all the way up, I *can* make it smoke a little, but the analog boost gauge still doesn't go above 20 (it seems to trail the electronic reading from my Scangauge-D) but the electronic only says 22.5 at WOT.



I'm still slowly investigating the potential of a boost leak elsewhere in the system, but I don't think it has one. I just think that's all the turbo can give. At 22+ psi, that is a LOT of air to move to stuff more in.



I'm not looking to lower EGT though, b/c flat ground at 70mph while towing a Jeep is about 800 degrees - right where it should be. Even climbing some grades it tops out at about 1100 degrees, that's all there is for heat. Pre-turbo, in the #6 port right now.
Interesting concept..
I am a gas guy. This is my first diesel. Gas reacts quite the opposite.
More air with the same fuel, Lean, = hotter EGT's
Diesel don't act the same??
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Old 10-15-2021, 06:31 PM   #11
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Diesels are lean burn engines. There is no throttle on them. Injecting more fuel is the only RPM control.
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Old 10-15-2021, 10:46 PM   #12
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Originally Posted by 98fleetwood View Post
Interesting concept..
I am a gas guy. This is my first diesel. Gas reacts quite the opposite.
More air with the same fuel, Lean, = hotter EGT's
Diesel don't act the same??
Nope. You aren't alone in not knowing that diesels are the exact opposite - there are many scientists and performance people who SHOULD understand this, who haven't a clue about it either.

When a gas engine is working hard and running hot, you ADD fuel (run rich) to lower the EGT and avoid melting a piston. Gasoline engines MUST operate in an excess of fuel, and after the combustion event, there will be unburned hydrocarbons existing in the exhaust - which is why gas engines also benefit from EGR, b/c it brings that unburned fuel back around to the intake for another go at turning it into power instead of wasted emissions out the tail.

On a diesel engine, when it is working hard and running hot, you have to ADD AIR or CUT FUEL to cool things down, or you will again melt a piston. This is because a diesel is a LEAN BURN engine - there must ALWAYS be an excess of air, so that at the end of the combustion cycle ALL the fuel has been consumed. Running a diesel rich does nothing more than waste fuel and make smoke (morons who "roll coal") and this is NOT HELPFUL or desired, and spikes the EGT for no good reason.

This lean burn characteristic is also one reason why diesels DO NOT need or benefit from an EGR system - there is no unburned fuel to recirculate, and introducing non-oxygen exhaust into the intake only reduces the air/fuel mix and brings the engine closer to running rich! There is no benefit.

At idle, a diesel engine is operating at nearly 250:1 air:fuel. Under load, this may reduce down to as low as 25:1. A gas engine ALWAYS wants to be operating as close as possible to 14:1, but for various reasons, this is often much lower, around 11:1.
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Old 10-18-2021, 08:09 PM   #13
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Aluminum in engines begins to soften at between 1250 - 1,300F when measured pre-turbo. Pure Aluminum melts at 1,220F
https://www.engineersedge.com/materi...ures_13214.htm


For those new to diesel engines, this explains how and why a diesel engine works: https://learning.hccs.edu/faculty/hu...gine-operation
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Old 10-19-2021, 07:13 AM   #14
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Nope. You aren't alone in not knowing that diesels are the exact opposite - there are many scientists and performance people who SHOULD understand this, who haven't a clue about it either.



When a gas engine is working hard and running hot, you ADD fuel (run rich) to lower the EGT and avoid melting a piston. Gasoline engines MUST operate in an excess of fuel, and after the combustion event, there will be unburned hydrocarbons existing in the exhaust - which is why gas engines also benefit from EGR, b/c it brings that unburned fuel back around to the intake for another go at turning it into power instead of wasted emissions out the tail.



On a diesel engine, when it is working hard and running hot, you have to ADD AIR or CUT FUEL to cool things down, or you will again melt a piston. This is because a diesel is a LEAN BURN engine - there must ALWAYS be an excess of air, so that at the end of the combustion cycle ALL the fuel has been consumed. Running a diesel rich does nothing more than waste fuel and make smoke (morons who "roll coal") and this is NOT HELPFUL or desired, and spikes the EGT for no good reason.



This lean burn characteristic is also one reason why diesels DO NOT need or benefit from an EGR system - there is no unburned fuel to recirculate, and introducing non-oxygen exhaust into the intake only reduces the air/fuel mix and brings the engine closer to running rich! There is no benefit.



At idle, a diesel engine is operating at nearly 250:1 air:fuel. Under load, this may reduce down to as low as 25:1. A gas engine ALWAYS wants to be operating as close as possible to 14:1, but for various reasons, this is often much lower, around 11:1.
Thx for your insight!
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