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ISX

12V IAT Readings

22 posts in this topic

Everyone seems to know the IAT of a 24V, but I never see anything on a 12V. So I cut the IAT wires, soldered wires to them, ran them into the cab, crimped them onto my multimeter leads, and I was able to read Ohms while driving. I am still working on a calculator to see what temps I am seeing but so far here is what I have personally tested, I just need a way to connect the dots for the calc.

Posted Image

I made a video of the test run. Engine wasn't started so I knew that 77F must have been 10kOhm.

One thing to note is that the computer was smart enough to know it had no continuity in the IAT wire and the WTS light blinked the entire time the key was on.

http-~~-//www.youtube.com/watch?v=Cy2XpWRSvgA

You can see that EGT and IAT have no relationship. You can see that air being compressed (BOOST) is what drives the temp up. At then end of the video there is a short clip of me idling after the run. The IAT is going up steadily because the turbo is hardly pushing any air. This allows the air in the intake to slowly swirl around and pick up heat from the engine itself, causing the air to heat up.

If you look at the table, you see that 116.5F is 4.1kOhms, so I wasn't getting anywhere near it.

Remember, lower resistance means HOTTER temps!

--- Update to the previous post...

Alright I got everything to temps x5 so I got results from 70-100 in the table now. PITA but I wanted to see exactly where it was. From what I can tell, I maxed out around 95 or so. That was almost to the floor when it got there, but only 18F over ambient. I was up to temp by that time but I still want to see what I get on an actual trip that takes longer than 3 minutes, when everything in the engine bay has got to whatever temp it wants to be at.

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On a 12V the IAT is only used for grid heater operation correct?

Yep, that's all it does. Only side effect is the blinking WTS light. I kinda like it :lmao:

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What's funny is I just ran it around again and it's 87F too :lmao: Now that I got some ohms to go by I watched it like a hawk and it never went less than 6 kohms or 100F and that was from 60-90 going up a steep hill. So I can't figure out why yours likes to run hot. I notice AH64 said in another thread how his seemed to only vary the amount mine does. I wonder if its just a VP44 truck thing, though I wouldn't think so. Let me do some more testing over the next couple days and see how hot I can get it. Maybe your air filter is clogged :lol:

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post-2-138698168304_thumb.jpg No it kind of hard to see cool temp reading when the IAT sensor is surronded by coolant passages... :wow: As for my air filter the filter minder isn't moving... Yes I tested it and it still works...

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Maybe it's the angle, but I thought the one you have labeled as the coolant passage was a plug from head machining, and had the #6 cylinder behind it, not coolant.

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Yea the 1/2" pipe plug just forward of the IAT I pulled that first time for my boost gauge and got a green bath... :mad:

Then learned the 3/4" pipe plug is the boost port which is forward of the MAP sensor.

post-2-138698168312_thumb.jpg

Posted Image

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Gotcha.. What about the freeze plug? I know on the 3rd Gen head that its not a freeze plug, but a machining plug.

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Now that possible... But from what little I can see from the bottom or cramming my head in from the drivers side it looked to be a standard coolant freeze plug and being there is a coolant passage just forward of the IAT I gather that would be too... I'll do some more digging on this...

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I'm still going to say you have bird feathers in your intercooler :lol:The whole trip yesterday it never got over 20F over ambient, and was mostly around 10-15 over.

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In this pic the plug right below #10 is a machining port, so there is manifold air behind it, not coolant. There is a similar port on the front, but the CP3 blocks it in the line drawing.

I would assume a similar access port was needed to machine the 24V head?

Posted Image

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https://spreadsheets.google.com/ccc?key=0AhHyLR2_DBOgdGhnRFgxR210Y1BWeFRWekFEbG1ZM0E&hl=en the outdoor temp was 24*F when this file was made you can see that my IAT never read lower than 68 and was even at 86 while in the driveway warming up thats a 44+ difference!

So its a 24V thing... I did a coolant flush today and found lower part of both the radiator and intercooler were packed with mud. so after getting it all said and done I'm now down to +35*F offset now... Now bad to lose 5 degrees of manifold temp. :thumbup2:

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I hit a new low with cruise IAT's a few weeks ago. Between Winchester and Lewiston, ID I ran 3-6* above ambient for about 25-30 miles, while its mostly downhill I have never ran that cool before.

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Well during our brief get together in the Chevron parking lots you now understand the 24V's problem of placement now. 12V and CR are lucky to have the sensor in a good place and show close to normal temp instead of offset temps because of coolant jackets and poor air flow...

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Yep, it makes me wonder if you could get more power by reading from the same spot the 12V/HPCR do? Would the ECM fuel harder or softer with the cooler IAT's? I really think the air hitting the cylinders is the same in all 3 engines, just the placement on the 24V is suboptimal.

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As from what I found out with accidential use of the IAT sensor fooler from my high idle mod I can set it for 26*F or 13*F IAT temps. From what occurs is uncontrolled smoking even with the Edge Comp OFF from the get go and much lower MPG's. :rolleyes: The colder the IAT becomes the more smoke and less MPG I get... Like I meantion before right around 90-110*F IAT temp is the best for MPG's.

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As from what I found out with accidential use of the IAT sensor fooler from my high idle mod I can set it for 26*F or 13*F IAT temps. From what occurs is uncontrolled smoking even with the Edge Comp OFF from the get go and much lower MPG's. :rolleyes: The colder the IAT becomes the more smoke and less MPG I get... Like I meantion before right around 90-110*F IAT temp is the best for MPG's.

I am sure the 15lb brain guys at Cummins have it pretty well dialed in for how the sensor sits and reads.

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I am sure the 15lb brain guys at Cummins have it pretty well dialed in for how the sensor sits and reads.

I agree :iagree: I think the ECM software has been program to understand the offset and deal with its location... I think where things go bad is when people relocate the sensor like to the 3rd gen or 12V location or up on the intake elbow...

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