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12V IAT Readings


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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.

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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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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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  • Staff

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?

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  • Owner

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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  • 4 weeks later...
  • Owner

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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