# What are normal Intake Air Temps?



## BodhiBenz1987 (Jan 13, 2018)

Just curious where the different air intake temperatures are taken and what they should be. I have two X Gauges, IA2 and IA3, but I would assume there is a IA1 as well. IA3 is always the highest so I assume this may be post-turbo, pre-intercooler? IA2 is a little lower but seems to get kind of high around town (120 on a hot day). What's normal for these readings? Anyone else track them? I'm a little OCD but after 8 months of frequent regens still no answers so I keep a log of any data that seems relevant and might be helpful to the dealer if issues arise in the future.


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## oregon_rider (Jul 21, 2017)

parts fiche shows intercooler has 2 of the intake temp sensors - one at input and one at output of intercooler.

https://www.trunkmonkeyparts.com/v-...t--1-6l-l4-diesel/cooling-system--intercooler 

jeff


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## BodhiBenz1987 (Jan 13, 2018)

oregon_rider said:


> parts fiche shows intercooler has 2 of the intake temp sensors - one at input and one at output of intercooler.
> 
> https://www.trunkmonkeyparts.com/v-...t--1-6l-l4-diesel/cooling-system--intercooler
> 
> jeff


 Thanks Jeff, I had looked at a couple parts catalogs but didn't see those pictures. That would explain why one is high (right after turbo) but I'm a little concerned about the other since you would think that one should be close to ambient and mine goes 30+ degrees over ambient at times. But I'm not sure so I guess I should try not to worry too much. I am really curious what others typically see for those temps.


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## oregon_rider (Jul 21, 2017)

The turbo pressurizes the intake air and this will increase it's temperature. Both the sensors in the pic above are after the turbo (compressed air) and will be higher than ambient temps... The purpose of the intercooler is to bring the temps back down to further increase the density of the intake air (to increase efficiency).

jeff


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## BodhiBenz1987 (Jan 13, 2018)

oregon_rider said:


> The turbo pressurizes the intake air and this will increase it's temperature. Both the sensors in the pic above are after the turbo (compressed air) and will be higher than ambient temps... The purpose of the intercooler is to bring the temps back down to further increase the density of the intake air (to increase efficiency).
> 
> jeff


I wasn't clear on that sorry, I knew they were both after the turbo, but one is after the turbo AND after the intercooler, correct? If I'm looking at it right? So I would expect post-turbo, pre-intercooler to be pretty hot, but I was under the impression post-intercooler would see temps a little closer to ambient. I've read 10-20 degrees higher than ambient a few times in reference to other cars and not specific to operating conditions, so I really don't know if that's relevant to ours.


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## Barry Allen (Apr 18, 2018)

BodhiBenz1987 said:


> I'm a little concerned about the other since you would think that one should be close to ambient


Getting intake air temperatures close to ambient requires either a huge intercooler, a long dwell time for the air in the intercooler to exchange heat, or a combination of both. And then you have to have adequate ambient airflow past the intercooler to exchange heat.

The amount of air being pumped through the intercooler is just too much to drop temperatures close to ambient. The air is too hot from lots of boost (up to 27psi?) that is far above what is peak boost for gassers. And these are small cars, so the intercooler isn't a huge size like what you could fit on the front of a 250/2500 pickup truck.

The good news is that diesel engines aren't negatively impacted by high intake air temperatures. Gasoline engines have detonation problems. Drive a turbocharged gasoline engine in Phoenix during summer and you can experience the ECU pulling boost because intake air temperatures are too hot. You can fill the fuel tank with 91 octane (93 if you can find it) to help a bit, but it's still an issue. Diesel engines thrive on hot cylinder temperatures because it ignites and burns the fuel better.

Really, the only reason a lot of diesel engines uses intercoolers is for emissions reductions. They need lower peak combustion temperatures to reduce NOx creation. If we didn't have to worry about NOx emissions we could entirely eliminate the intercooler and have the compressor dump straight into the air intake with the shortest path possible (and this would reduce compressor lag a bit).


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## BodhiBenz1987 (Jan 13, 2018)

Barry Allen said:


> Getting intake air temperatures close to ambient requires either a huge intercooler, a long dwell time for the air in the intercooler to exchange heat, or a combination of both. And then you have to have adequate ambient airflow past the intercooler to exchange heat.
> 
> The amount of air being pumped through the intercooler is just too much to drop temperatures close to ambient. The air is too hot from lots of boost (up to 27psi?) that is far above what is peak boost for gassers. And these are small cars, so the intercooler isn't a huge size like what you could fit on the front of a 250/2500 pickup truck.
> 
> ...


Thanks for the explanation, that's really helpful and makes sense. I'd been trying to kind of piece together what I should expect based on things I hear in the car world in general, not just diesels. I do have a non-intercooled turbodiesel that runs great and is reasonably powerful (on par with the Cruze in terms of highway passing) so I did wonder about how much an intercooler did.


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## Barry Allen (Apr 18, 2018)

BodhiBenz1987 said:


> I do have a non-intercooled turbodiesel that runs great and is reasonably powerful (on par with the Cruze in terms of highway passing) so I did wonder about how much an intercooler did.


Diesel engines are almost always running lean on fuel. There is almost zero benefit to cooling the intake charge to make it more dense (more oxygen in the cylinders) because it's not of any benefit to a diesel engine when it's already lean on fuel.


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