Input Air Temp. IAT. What should it be???

[Meathead]

I have a Cat3126b, 2001 Thomas HDX pusher. She’s running great. Last year a bought a Bluefire adaptor so I have a lot more information than I used to have. I’m happy with my coolant and trans temperatures. My input air runs about 50 degrees hotter than the ambient temp.
New oil
New coolant
Transynd 1 yr old. 8k miles
New air filter

Typical last summer in hotass Kansas.
Ambient temp. 95*
Coolant temp. 192*
Trans temp. 175*
Speed. 62 mph
RPMs 2000
IAT. 145-150*

Normal?
Too High?
What do y’all think?

Thanks in advance!
Dave

OH….Also runs 45-50* higher at ALL outside temps.

 

[Meathead]

So I might have figured it out. Intake heater is stuck on? Relay not working or a ground wire is rubbing/touching and going to ground?

I’m going to disconnect. Haha. I live in the Deep South. I don’t need no stinking heater! The coldest I’ve ever started my bus was about 25*F. That’s butt cold for us southern boys. After testing my theory I’ll prolly fix the problem. Ya never know what you’ll need down the road. I kept my automatic rear tire chains just in case.

I guess the point is - I would never have known this was happening if I didn’t have the Bluefire Adaptor.

Dave

 

[ewo1]

So I might have figured it out. Intake heater is stuck on? Relay not working or a ground wire is rubbing/touching and going to ground?

I’m going to disconnect. Haha. I live in the Deep South. I don’t need no stinking heater! The coldest I’ve ever started my bus was about 25*F. That’s butt cold for us southern boys. After testing my theory I’ll prolly fix the problem. Ya never know what you’ll need down the road. I kept my automatic rear tire chains just in case.

I guess the point is - I would never have known this was happening if I didn’t have the Bluefire Adaptor.

Dave

help me out here as I really only understand the international (dt466e) motors.
IAT- stands for Inlet Air Temperature.
This is only a sensor that tells the computer what the current air temp is while the engine is running. it has no moving mechanical parts.

How could it be "stuck on"? It can't in my mind. there are NO moving parts.
It is nothing more that just a basic "thermistor" if you will, voltage will change as the temp on the sensor surface changes telling the computer what to do with the air/fuel mixture.

I ask myself, and you too, do you mean to say that "Stuck on" is simply the sensor shorted out? zero ohms when you resistance check the terminals?

I am totally unaware of the actual wiring in your bus/engine but I am trying to say/ask why there would be a relay involved when this IAT signal must be present 100% of the time while the engine is running and is not dependent on a wakeup signal from a relay in order to talk the the ecu.

I'm not working against you just looking to put things in my mind a bit clearer...

 

[ewo1]

oh,,,ok, I just learned something about a Cat...

Dr. Google shared this with me...

The Caterpillar 3126B IAT (Intake Air Temperature) sensor is crucial for engine performance, particularly in cold conditions. It measures the temperature of the air entering the engine, allowing the Electronic Control Module (ECM) to adjust fuel injection and timing for optimal combustion. This sensor is part of a system that includes an engine grid heater in the intake manifold to warm intake air before it enters the cylinders.

• Troubleshooting:
  If the IAT sensor fails or provides inaccurate readings, it can lead to a variety of issues, including poor starting, hesitation, and reduced power.

So correct me if i wrong, what your really saying is that your grid heaters are STUCK ON and not the IAT....

Yeah living in the south you won't need them much....
If your wait to start light is working properly I would just remove the heater grid relays, put them in a ziplock pouch and store it on the bus with all the other spare parts you got..

 

[ewo1]

So your first post says he IAT runs 50 degrees hotter than the ambient temp...
I would test with another IAT if possible or use a laser temp gun, pull the sensor and read the tip, install quickly and check the screen reading. 50 degree is a huge temp swing, especially in HOT country !!!

 

[Cheezewhiz]

That's post turbo though, yeah? Turbos heat up the air they shove a good bit, hence the intercooler situation.

I assume the sensor is on the intake manifold.

Because +50 at the manifold is, well maybe a little high. Maybe. Got leaks in the intercooler?

 

[Mr P]

Any time air is compressed, it's temperature rises. The intercooler reduces that heat, but is not 100% efficient. A 50 degree rise is probably normal. See if the temp rises under high boost vs low boost (pulling a hill at WOT vs coasting down the hill)).

 

[Meathead]

oh,,,ok, I just learned something about a Cat...

Dr. Google shared this with me...

The Caterpillar 3126B IAT (Intake Air Temperature) sensor is crucial for engine performance, particularly in cold conditions. It measures the temperature of the air entering the engine, allowing the Electronic Control Module (ECM) to adjust fuel injection and timing for optimal combustion. This sensor is part of a system that includes an engine grid heater in the intake manifold to warm intake air before it enters the cylinders.

• Troubleshooting:
  If the IAT sensor fails or provides inaccurate readings, it can lead to a variety of issues, including poor starting, hesitation, and reduced power.

So correct me if i wrong, what your really saying is that your grid heaters are STUCK ON and not the IAT....

Yeah living in the south you won't need them much....
If your wait to start light is working properly I would just remove the heater grid relays, put them in a ziplock pouch and store it on the bus with all the other spare parts you got..

Yes you are correct. The IAT reads 50* higher at any outside temp. There is a relay when activated by the ECM that turns on the intake air heater. Yes I think that the relay is stuck/broke and my intake heater is on all time! Crap! I will be disconnecting the relay today and taking a test drive. 5-10 miles should do it. For those following along see the attached fotos.

If you have a 3126 and you don’t have a way to read your input air temp maybe you should check your relay. I imagine a cooler running engine and better fuel mileage??
Whoo!

 

[Mr P]

Did you miss the posts # 6 and 7?


50 degree rise from ambient is very likely normal. The intake heater preheats for cold starts, that's at cranking speed, which is very little air volume compared to running at 2000 rpm. I doubt the intake heater produces 50 degrees of rise at cranking speed, and would have very little affect on temps at 2000 rpm.

 

[Meathead]

Yes I did. Thank you for answering my original question “Is this normal”. It sounds like it could be! I will test that on the Mississippi River bridge later this week.( there aren’t any mountains near here). My boost ranges from 0-20%. Does that sound normal? (again my new Bluefire gives me data I don’t know what to do with).

Thanks for your input!
Dave

 

[Meathead]

That's post turbo though, yeah? Turbos heat up the air they shove a good bit, hence the intercooler situation.

I assume the sensor is on the intake manifold.

Because +50 at the manifold is, well maybe a little high. Maybe. Got leaks in the intercooler?

I will check for leaks. Those hose connections are pretty old. Thanks!

 

[Meathead]

Update. So I disconnected the pre heater and ran my bus uphill twice.(over the misssissippi river and back).
85* ambient
Bus warmed up coolant190*
IAT = 110 @ bottom of hills
IAT = 140 max for the entire trip. 30min
IAT after 3 flat miles = 115*

How does that sound?
I plan to clean my radiator, cac, and a/c coils
next week to make sure I’m running as cool as I can. I’ve seen guys add an additional fan on RE busses. Do y’all think this would help? Can’t hurt?

Thanks
Dave

 

[Mr P]

So, if you'd driven over the same hill twice on the same day, once with the heater plugged up, the other without, you'd have better data to compare. Do you think the heater is a non-issue?

 

[Meathead]

So, if you'd driven over the same hill twice on the same day, once with the heater plugged up, the other without, you'd have better data to compare. Do you think the heater is a non-issue?

Yep,prolly non issue.

 

[Cheezewhiz]

****, I think that sounds pretty good. If your coolant is staying stable, I don't see an issue. Transmission temp good too?

We've been in some mountains in 95 ambient, and have been having a bunch of overheating issues. Old filters, mostly.