Why is IAT temp always higher than ambient?

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 292

IAT= temp sensor on airbox. Seems like it should be at ambient temp. What am I missing?

gmctd · **Posted:** Sun Jan 04, 2015 2:19 am

Also the Intake Air Temperature sensor, part of the MAP sensor, which would be warmer (hotter) than ambient measured at the air box - ECM will pull fuel if manifold intake (BOOST) air temp gets too high, indicating likely ambient air-flow blockage thru the CAC

Problem being, I use these scantools:
EDGE
DRBIII
STARSCAN
ScangaugeII
AUTOENGINUITY Global
AUTOENGINUITY Enhanced
ECU Titanium
VagCom
Elm327
etc........

Manifold temperature is called, variously:
Intake Air Temp
Manifold Air Temp
Boost Air Temp
Charge Air Temp
Compressor Air Temp
Turbocharged Air Temp

No oem's seem to want to settle on one definition so it takes some reading between the lines

flash7210 · **Posted:** Sun Jan 04, 2015 8:59 am

Most of the various scan tool thingys get the intake air temp from the MAP sensor which is on the intake manifold.

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 292

flash7210 wrote:

Most of the various scan tool thingys get the intake air temp from the MAP sensor which is on the intake manifold.

Okay...but...we have a temp sensor sitting right there on our airbox. And yes, a MAP sitting over on the other side of the engine. What is using the temp sensor on the airbox? My scan tool seems to show two different readings and if your theory is correct those readings are coming from the same sensor?

diesel_guy86 · **Posted:** Sun Jan 04, 2015 10:11 am

Using torque pro, I can only see the temp from the tmap sensor in the manifold. It's always warmer than ambient because 1) a turbos compressor is at most 70%-75% efficient, meaning it creates heat as it compresses the air. And 2) heat soak back into the aluminum intake system.

ArmyChief · **Posted:** Sun Jan 04, 2015 11:25 am

gmctd wrote:

Also the Intake Air Temperature sensor, part of the MAP sensor, which would be warmer (hotter) than ambient measured at the air box

There is no temp sensor on the airbox. Only the MAF (used for EGR) and the inlet pressure sensor (used for plausibility for boost). The only other air temp sensor is the one on the front grill used for the EVIC and glow plug control.

ArmyChief · **Posted:** Sun Jan 04, 2015 11:26 am

taroo wrote:

Okay...but...we have a temp sensor sitting right there on our airbox.

See my reply above

flash7210 · **Posted:** Sun Jan 04, 2015 11:39 am

taroo wrote:

flash7210 wrote:

Most of the various scan tool thingys get the intake air temp from the MAP sensor which is on the intake manifold.

Okay...but...we have a temp sensor sitting right there on our airbox. And yes, a MAP sitting over on the other side of the engine. What is using the temp sensor on the airbox? My scan tool seems to show two different readings and if your theory is correct those readings are coming from the same sensor?

The inlet pressure sensor on the airbox is something that is unique to this engine. Not all scan tool thingys are going to support an obscure sensor.

What two readings is your scan tool giving you?
Are they intake temperature readings or are they ambient temperature readings?

flash7210 · **Posted:** Sun Jan 04, 2015 11:42 am

BTW, i disconnected the inlet pressure sensor on the airbox just to see what would happen.
I got a P1186 and P1189 codes but other than that it seems to drive just fine.

ArmyChief · **Posted:** Sun Jan 04, 2015 11:52 am

flash7210 wrote:

BTW, i disconnected the inlet pressure sensor on the airbox just to see what would happen.
I got a P1186 and P1189 codes but other than that it seems to drive just fine.

Yea, I kinda figured that. A circuit for a dash light could EASILY be designed for air filter reminder from that sensor.

gmctd · **Posted:** Sun Jan 04, 2015 12:28 pm

ArmyChief wrote:

gmctd wrote:

Also the Intake Air Temperature sensor, part of the MAP sensor, which would be warmer (hotter) than ambient measured at the air box

There is no temp sensor on the airbox. Only the MAF (used for EGR) and the inlet pressure sensor (used for plausibility for boost). The only other air temp sensor is the one on the front grill used for the EVIC and glow plug control.

MAF has temperature sense or air density could not be calculated for mass

ArmyChief · **Posted:** Sun Jan 04, 2015 12:51 pm

gmctd wrote:

ArmyChief wrote:

gmctd wrote:

Also the Intake Air Temperature sensor, part of the MAP sensor, which would be warmer (hotter) than ambient measured at the air box

There is no temp sensor on the airbox. Only the MAF (used for EGR) and the inlet pressure sensor (used for plausibility for boost). The only other air temp sensor is the one on the front grill used for the EVIC and glow plug control.

MAF has temperature sense or air density could not be calculated for mass

gmctd,

Although you are TECHNICALLY correct. The air temp sensor is INTERNAL to the MAF circuitry used for calculation purposes to output a analog voltage in proportion to airflow. So, as it pertains to the OP's original post about air temps on his scan tool...I stand by my answer(s).

gmctd · **Posted:** Sun Jan 04, 2015 1:49 pm

Correct on both - and, tnx for posting that - saved me some time, as I intended to explain further with calcs soon as I finished feeding\walking the dogs and draining\reconditioning the holding tanks - one 5v supply is the electronic module, t'other is the precision current sense for temp\humidity variations

ArmyChief · **Posted:** Sun Jan 04, 2015 1:53 pm

Took me almost 10 minutes to put that page together. Cut and paste from two different sections of the FSM and then upload to imageshack!

I only would do that for a great friend

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 292

ArmyChief wrote:

Took me almost 10 minutes to put that page together. Cut and paste from two different sections of the FSM and then upload to imageshack!

I only would do that for a great friend

Okay..so....I believe I am hearing it is a MAF and a Intake Pressure Sensor. I am posting the pic of what my ScanTool is/was reading. It is/was reading Intake Air Temp and I thought that was coming from the airbox sensor but you folks have shown me that the Intake Air Temp is coming from the MAP sensor post compression and intercooler. The outside temp was in the upper 30s and you can see that the Intake Air Temp is showing 90 degrees F.....ergo my original question. Thanks for the education.

By the way...had a whistle after my TB, WP, ARP, Weeks Kit (EGR.FCV, EGR Cooler elimination) and just found it. It was a clamp on the driver side CAC not tight enough. So....I am good for another 100K miles. Just waiting now for the vent pod and 0-35 PSI boost gauge from Seth to install so I can see the Boost pressure.

Here is my ScanTool reading I was referring to:

ArmyChief · **Posted:** Sun Jan 04, 2015 5:40 pm

Glad we could help! :BANANA:

diesel_guy86 · **Posted:** Sun Jan 04, 2015 10:21 pm

WOW! 90° seems ridiculous. In the mid to high 30s ambient I'm around 50-60° IAT, hitting 90° or a lil over on a full throttle takeoff.

To be fair though I'm using a different turbo than the factory so maybe that's where the difference is. Plus I also flushed out my intercooler to get as much effectiveness as possible from it.

ArmyChief · **Posted:** Sun Jan 04, 2015 10:32 pm

diesel_guy86 wrote:

Plus I also flushed out my intercooler to get as much effectiveness as possible from it.

Did you remove to do that?..How may I ask and what chemical?

Did much oil come out?

diesel_guy86 · **Posted:** Mon Jan 05, 2015 12:11 am

My original tb sheared off a bunch of teeth at 148k miles, I went the route of removing the front end so the intercooler was out anyways. I just used gas and yes a lot of oil came out, took several times till clean gas came out. I'd pour roughly a quart of gas in, cap off each port and shook it all around. I used gas cuz it's cheaper than any other cleaning agent, and it evaporates.

What's even more scarier is the amount of crud in your intake manifold. Took 3 hot tank sessions at the machine shop to get it all out.

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 292

diesel_guy86 wrote:

WOW! 90° seems ridiculous. In the mid to high 30s ambient I'm around 50-60° IAT, hitting 90° or a lil over on a full throttle takeoff.

To be fair though I'm using a different turbo than the factory so maybe that's where the difference is. Plus I also flushed out my intercooler to get as much effectiveness as possible from it.

Hmmm....so...90 degrees is high? Okay folks...what should the increase be from ambient? You owe this to the turbo fan or the Intercooler? Sasquatch does sell a different turbo fan. Would that help? What am I dealing with here? I will run the ScanTool again to check out the delta.

Why is IAT temp always higher than ambient?

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