What is an IAT Sensor?

[cD'amato]

What is an IAT Sensor and is it hard to change?

 

[KatDiesel]

Intake Air Temperture sensor.



See this for some info on changing/cleaning it.



Exactly what your looking for

 

[IdaH.O.Train]

Have fun

I decided to take a look at the IAT sensor when I did my first service. Maybe it's just me, but trying to manuver your arm back there and get the retaining clip off was a real PITA! It took me a half hour to get off and when I finally did, the GD thing was squeaky clean.

 

[cD'amato]

IAT

The reason I ask is Ive got 40k miles on my 99 now and my Fuel Mileage seems to have dropped a bit and siting around 14MPG around town. From what I gather, replacing(or cleaning) this may or may not help.

 

[Chipstien]

Looks aren't everything.

I took mine out and it was spotless but sprayed it anyway... . now the wait to start light stays on half as long. Amazing how little oil can effect that sensor.

 

[Alan Reagan]

The sensor is actually a thermistor with a very fast reaction time to changes in temperature. A little oil does make a lot of difference. If you are running an exhaust brake you need to check them pretty often.

 

[Pit Bull]

Originally posted by Alan Reagan

The sensor is actually a thermistor with a very fast reaction time to changes in temperature. A little oil does make a lot of difference. If you are running an exhaust brake you need to check them pretty often.

How often would you check if you are not running an exhaust brake?

 

[dresslered]

Alan-

You are saying exactly what many others are claiming. I'm just having a real tough time understanding the mechanism for the claimed poor performance? I fully understand how thermistors work, but I truely can't believe that a dirty thermistor would cause any faulty readings. At the very most, it might only cause a slight delay with its changing resistance to a rapid change in ambient temperature (intake air). I don't believe that this is critical to its used application, however. Once the truck is up and running, the temperature will stabilize and the thermistor will settle into place regardless to the dirt (insulating properties) surrounding it. Now if actual resistance characteristics have changed, then this is another story and a simple cleaning is not going to rectify the problem anyway.



I would think that the MAP sensor is much more delicate and possibly even becomes damaged when used in high boost applications. Both sensors are used to calculate the proper air/fuel mixture.



Just a thought...

 

[Alan Reagan]

Dresselered, My IAT was out of measurement parameters from Marcos work last year by about 2Kohms if I remember right. After I changed the IAT, my exhaust smoke lessened and fuel mileage increased. Mine had a brown haze on it and the measurement was off. This could be an error of correlation. I don't know. That's what I'm basing my observation on. With the exhaust brake, exhaust is actually forced back into the intake void when the brake is on because the one I saw out of an e brake equipped engine was black. If I'd kept my old one I would experiment with it but the dealer took it on warranty. I don't know if the haze that's forming is a good heat conductor or what but 2000 ohms is a lot of error in that sensor. Also, I looked at one out of a 99 and the thermistor was touching the case. We played with it a little and changed the resistance by moving the thermistor package off the protective brass case. It improved the owner's mileage, too. I think in that case, the thermistor wasn't measuring the intake air temp, but the temperature of the protective brass enclosure.

 

[dresslered]

I definitely agree that a 2k shift in resistance would explain the performance issues. I can also believe that if the probe is bent (out of the air stream) or touching the manifold (heat sink) you may get faulty readings as well. I just find it hard to believe that a layer of soot is going to account for a temperature gradient that would alter the readings significantly. Also, if you are obseving a change in resistance by moving the thermistor package, this is not good either. I wonder if there is a problem with the solder joints (cold)? I have an exhaust brake on my truck and have not looked at the sensor yet. I will be very curious to see the deposits as well as take some resistance measurements. I'm wondering if the carbon deposits are providing another conductive path which would then account for a lower resistance than normal?



P. S. My mileage has always been 15mpg since new. I now have over 35k. It doesn't seem to be degrading at all, but it isn't what others are claiming either.

 

[Alan Reagan]

Dresselered, I don't know if the carbon provides a conductive path or becomes an insulator. As an electrical engineer, I find it hard to believe that the soot or haze can affect these things, but they are sensitive. Very sensitive. I have never seen specs on what coatings do to them and have never worked in an environment where the thermistors getting dirty was a problem. All of this is speculation on my part where I'm seeing something and trying to figure out what the cause is. I get over 21 mpg most of the time and I believe (again I'm speculating) that it is a combination of small things I've done rather than one big fix. Changing my IAT was one of them. Cleaning mine didn't do very much but it did a little. One more observation so you get the whole picture. When I first went to clean mine, I put the socket on the sensor, got the extension in and snapped in the ratchet. It took almost zero pressure to turn the sensor. When I put it back in, I snugged it up good to seat the O ring. That probably helped, too.



Pit Bull, I check mine at 20K. I think it can tell you alot by looking at it. For instance, if you run a oiled air filter, that will definitely affect the performance of the IAT if oil is getting on it. All the ones I've looked at without the E Brake have a brown haze like spark plugs get. Be careful not to break the thermistor off during cleaning. E Brake ones I've seen actually have a coating of black soot. I used brake cleaner and Q tips and it cleaned right up.



Dresselered, that makes me think. I wonder if the haze builds a "track" between the leads down inside the protective case and possibly changes the resistance. The haze track may be conductive enough to change the resistance. Don't know. And you can't get down in there to see.

 

[dresslered]

Thanks for the reply, Alan. I sent you a PM. One application where these thermistors are taking a licking and still ticking is in our pyros.