Which EGT do I believe??

[Cattletrkr]

1. Autometer with probe post turbo

2. Attitude with probe in manifold



Juice set on 1/5



I was pulling approx. 24K up a 1. 5mi. hill tonight. Kind of a light load for me so I decided to keep it in 6th and push it. I looked at the attitude and it read 1180*. Glanced up at the Autometer and it read 1125*. I immediately backed out of it and then decided to see how far the autometer would go. By the time I got over the crest, the two were reading almost the same, Attitude still on 1180* and the autometer just below, 1160 maybe. Speed remained a constant 67mph, maybe increased a little if anything.



I've suspected the Autometer to be "funny" since I installed it, long before I got the Attitude. With no Juice or Juice turned off, I can easily hit 1400*. That's sounds way too hot for a truck with no fuel mods. This gauge was in my '01 for a few months before I sold it and it gave "normal" reading while it was in that truck.



At lower EGT's, say normal cruising temp of 500-800*, they act about the way you'd expect them to. Maybe a 100-300* spread depending on load and rt. foot.



Is there something screwey with the autometer gauge once it gets over a certain temp? How do I check it? I've got a multi-meter, but I don't know what values I should be looking for.



Or is my attitude lying to me? I've had 2 or 3 different attitudes for various reasons. They all read the same.

 

[Mundgyver]

Do I understand correctly that you have one infront of the turbo in the manifold and one after the turbo in the down pipe



If this is correct, then with the info you have given, what you are showing looks normal. You will loose heat as you proceed down the exhaust system. Pulling the hill with power, is going to bring the two closer together as the later parts of the exhaust system warm up closer to the manifold temp.



In a steady state after cresting the hill they should be pretty close and then start to drift apart again if nothing changes.



I think what you are seeing is normal based on the seperation distance between the two, if you have one pre-turbo and one post (after) turbo.



Almost forgot, I have seen 1500* + for a few very brief seconds when in an uphill run and pulling out to pass. Not often (twice), but enough to keep my attention riveted now when I am passing on hills now.

 

[Nate]

Yeah some of those Oregon passes, like Deadman's Pass, are BAD!

 

[rjohnson916]

I was worried about this too. I've got an Autometer and Attitude monitor. I thought redundant guages would be great, but it's confusing the crap out of me. below 400 degrees the two are within spitting range. Ubove 400-500 degrees I get a spread between the two, the Autometer always reads higher??? My probes are within an inch of each other, on the top of the exhuast manifold pre-turbo.







-Ryan

 

[Scrappy]

I was worried about this too. I've got an Autometer and Attitude monitor. I thought redundant guages would be great, but it's confusing the crap out of me. below 400 degrees the two are within spitting range. Ubove 400-500 degrees I get a spread between the two, the Autometer always reads higher??? My probes are within an inch of each other, on the top of the exhuast manifold pre-turbo.







-Ryan

are they both in the same runner? if you have one in the front and one in the rear runner, the rear should be higher since it is more restrictive.

 

[JVolpe]

I had a Juice/Attitude pyro sensor and an Autometer Ultra-Lite installed at the same time. They were both pre-turbo. The Autometer sensor was between cyl 3 & 4, the Attitude sensor was about an inch closer to the rear. The Attitude pretty consistently read about 25-50* higher than the Autometer. This kind of made since since it was closer to the hotter cylinders, or so I have been told.



I now have the TST pyro senso in the same tap as the Attitude was and it varies about the same 25-50* from the Autometer. It is slower to respond to changes than the Autometer as was the Attitude. That is just the nature of digital gauges I think.

 

[Mundgyver]

One thing to remember, is that none of these gages has an offset calibration capability in them. What this means is that you have a known calibrated standard (Industry Jargon here) to measure against and also have the ability to input what is known as an off set either - or + to bring your gage reading in line to read the same as the calibrated standard which serves as the base model. Also, if two pryometers are in line with each other in the same runner, is there an eddy flow affect off of the first probe that can affect the flow of hot gas around the second one and does this create temperature reading differences. I think the answer will be yes it does. My knowledge of this subject is base on my work within the Hi-Tech Semiconductor industry working on annealing ovens and hotplates.



I think what your are seeing is the difference between manufacture preformance standards. The question is, what brand of gear or test equipment does the factory, i. e. Mr Cummins use as a standard when measuring these temps.

 

[Cattletrkr]

Do I understand correctly...

Sorta. Yes I do have one pre and the other one post. One mounting port in each general location. I would expect the post probe to "catch up" to the one in the manifold. However the real problem is when I switch probe locations.



I guess I edited my post before actually posting it and forgot what wasn't in there anymore. Here goes:



If I switch positions of the two probes, putting the attitude post and the auto. pre, I get vastly different results. The pre-autometer will climb easily to 1400*, I think I may have let it go to 1500* once just to see where it would stop. The pre-attitude will NEVER hit those temps unless I were to pull such a load on level 3 or higher, then it might. Both gauges show about the same temps when inserted post turbo. It's only on the upper end of the temp scale that I see a problem. That's where it can pose some serious heat issues.



In one position I see very little difference in temps. Switch things around and I see 200-400* differences as one would expect. Fine, so there's a "normal" 25-50* variance, but that doesn't explain such a drastic change.

 

[JApol]

The meters are calibrated to a certain amount of wire. Most thermocouples

are made of alumel and chromel. Each of these wires has approximatly 1 ohm

per foot. Since most pyrometers come with 8 feet of cable and you have

changed this lenght you have



1) created a cold junction that is not included with the readings.

2) created a longer/shorter wire that is not included in the readings.



A cold junction is a splice in a thermocouple wire harness that is not of the

same type of metal.

So if you have "adjusted" the length of your pyrometer wiring, i suggest

getting a new harness and getting the right temp readings.

 

[rbattelle]

I agree with what JApol says.



If you didn't extend the wires (or do anything else odd to the Autometer gauge), then I think that gauge is reading about 300-400 degrees high.



Pre and post turbo temperature are necessarily different because the turbine extracts energy from the flow. At low-load conditions, energy extracted is low, so the two readings should be pretty close to each other. At high-load conditions, the turbine is extracting a lot of energy and the readings will be quite far apart (perhaps as much as 500 degrees).



-Ryan

 

[Mundgyver]

What is being said by Rbattelle and JApol, I aggree with. One other thing that might make a difference also is the type of thermocouple used by each. One might be a type J and the other type T with would also create some confusion when switching around. I gather that you are not switching one probe to the opposite meter but instead are moving the probes locations. Is is a good assumption on my part?



A good calibrated standard would solve allot of the questions.

 

[Cattletrkr]

I gather that you are not switching one probe to the opposite meter but instead are moving the probes locations. Is is a good assumption on my part?

Yes.

Let me try this a different way:



Gauge = gauge, lead wires, thermocouple



Let's say I have only one hole drilled, tapped and ready for a probe. I have two different EGT gauges and each has its own complete thermocouple and wiring harness. I install Gauge A and it gives me a reading of 1200*F. I remove Gauge A and set it on the workbench. I then install Gauge B, which gives me a reading of 1500*F on the exact same run. How do I tell which Gauge is giving me the correct info???

If you didn't extend the wires (or do anything else odd to the Autometer gauge), then I think that gauge is reading about 300-400 degrees high.

Question is, Why?? Do I just need a new thermocouple? How do I go about testing it?

... and you have changed this length

I did??... ... ... . Really??... ... ..... When??

 

[rbattelle]

Question is, Why?? Do I just need a new thermocouple? How do I go about testing it?

Great question. I don't have any experience testing a thermocouple, so I'm not sure of a good way to go about it. If it were me, I'd probably put the probe in the oven and set the oven temperature to 450 degrees. Then see what the thermocouple reads. Do that with both gauges. You could also narrow down the number of possible fault locations using a temperature-capable multimeter, if you happen to have one.



Also beware that thermocouples require a cold junction temperature. That cold junction (which I presume is inside the actual gauge itself) needs to be at ambient temperature. Is there any chance either gauge's cold junction temperature points are in a place that causes them to be at anything other than ambient temperature? That's a long shot, but worth a check.



-Ryan

 

[Cattletrkr]

If it were me, I'd probably put the probe in the oven and set the oven temperature to 450 degrees.

hehehe... I trust the gauges more than I trust my 20+yr old oven...

Is there any chance either gauge's cold junction temperature points are in a place that causes them to be at anything other than ambient temperature?

The Juice has everything under the hood, so that could be too warm under there. Autometer is in the dash pod, nothing odd there.



I wonder if it makes any difference exactly where the wires are routed. I've never checked to see if one set is closer to a heat source than the other. Maybe I should try running them together in a loom, eliminate all variables and see what happens...

 

[Mundgyver]

Here is something that will help you understand the thermocouple. It is composed of two different metals. Each wire is different. The junction of these two wire (probe tip) will exhibit certain electrical properties during warming or cooling of the junction. This change in temp allows more or restricts less current flow to the gage or the interconnecting box before the gage, depending on the system. In reality, you have a resistor that is variable with what ever the applied surrounding temp is.



The different type probes, i. e. "J" type or "T" type, (there are others also) have different properties. Your gage will be calibrated to work with a particular type of probe.



Now we get into the offset that I mentioned before. Depending on the material used (probe type) and knowing that you can have two identical probe types "J" type and another "J" (this example) but by different manufactures, there can be subtle differences in the electrical properties of each when compared against each other. This difference can be very small, but enough to give you the spread of reading you are seeing.



If each gage with it's associated probe has a calibration factor that is adjustable (usually an interface box and some times on the gage if they have one) then you can calibrate one to the other or each one to a known standard. If calibrating to a known proven standard the procedure is straight forward, you just make the adjustment which is usually a variable pot in the direction needed until you match the standard. Some systems have 2 pots to adjust. One for the low side and one for the high side. These are the really expensive ones (thousands). Most have only one. Once you make the adjustment and bring the reading to the actual temp, then you need to walk away for a least 1 hour and let the system (gage adjusted) stabilize and then re-check and make further small incremental adjustments if required, each time letting the system stabilize.



If you want to calibrate one against the other then both probes are put into the same standard heat and allowed to stabilize. You then adjust the gages towards each other going only one half of the required distance in the adjustment and let stabilize. Repeat this until the two are the same. You will then be at the average between the two. This is a field method and works well. I have done this with multiple thermocouple harness on helicopter jet engine packs when I was in service. The end result, is you will be very close to actual temp.



Most individuals don't have the money for a calibrated standard so the field method works very well and it is fairly accurate for the average temp that we would see in our trucks. If you can borrow one (calibrated standard) then so much the better.



Hope this helps. There are others that have more knowledge than me. I don't remember all the technical terms. Getting into OldAge is hell



One last thing, heating the whole wire makes no difference, it is the tip junction (probe tip) that is where the action takes place.

 

[rbattelle]

One last thing, heating the whole wire makes no difference, it is the tip junction (probe tip) that is where the action takes place.

Mundgyuver, everything you said I agree with... except this sentence. As I understand it, a thermocouple works by temperature variation across the entire wire, from the tip to the cold-junction at the sensing mechanism (gauge). Link.



-Ryan

 

[Mundgyver]

You are correct, but the junction (Tip or the thermocouple junction) is the point at which the variable or variation of the resistance takes place. I agree that heating or cooling the entire wire will have an effect, (generally hotter means higher resistance and colder is less resistance in the wire) but the junction (tip of the thermocouple) itself is where the biggest affect is because of the two different metals used. That is why it is usually encased in a package that can be heat soaked or cold soaked depending on application.



In most application that I see, the junctions are encased by a couple of inches of SS outside sheath with a ceramic core. The probes we use in our manifolds look to be several inches long, but the part that counts the most, is the last inch of the probe tip.



Heating the whole length of wire will have an effect, but not near as much as heating the end where the junction is. An example, and I wish I had a picture of it is a set up that we use everyday where I work. They have a 6 inch silicon wafer, and taped down in the middle of this wafer is a thermocouple that is the size of a grain of sand with two hair thin wires coming out of it. The wire length is about 45 inches. They take this wafer and put it in an oven hotplate that is about 2 inches bigger than the wafer and close the door with the wire hanging out hooked up to the calibrated meter. We are looking for a temp of 300*C. Takes 4 minutes. If they are off by . 5*C the process is adjusted. This is the test gear. The oven that we are testing has it own thermal couple that has to match this test gear when we do this. If the oven is off temp, then we have to adjust the calibration factor of the gage so that it will read the same temp as the test gear and also send the signal to the controller to apply more power to heating elements or less power.



I have an Autometer gage in my truck and it has an interface box. I would have to pull it and look at it, because it has been so long since I installed the thing, but I think there is a pot on it that allows me to calibrate everything against a standard.



If I had the money, I would love to buy all the different Pyro gage setups that we as Diesel Heads use and test them all against a good certified standard. It would be interesting to see the variations between the units and it would make for a very lively thought process when published.



Maybe the manufactures could send me their units and I could set up a test

 

[rbattelle]

If I had the money, I would love to buy all the different Pyro gage setups that we as Diesel Heads use and test them all against a good certified standard. It would be interesting to see the variations between the units and it would make for a very lively thought process when published.



Maybe the manufactures could send me their units and I could set up a test

I seem to remember exactly this was done in a past TDR issue... can't remember the results.



-Ryan

 

[Cattletrkr]

This difference can be very small, but enough to give you the spread of reading you are seeing.

If that's the case, EGT gauges are completely worthless. I get a 300*F difference between the two gauges. Not worth looking at. No, I'm not talking about the difference between pre and post mounting. I'm talking about pre vs. pre... in the exact same port.

 

[Mundgyver]

No two gages even though they may be the same model are not exactly the same. There will always be very slight differences. That is why the ability to calibrate a gage to compensate for the differences is a nice thing.





The big trick is what standard, or who's (manufacture) standard is accurate.