I was reading up on the service manual and looking at my 08 4.0L Pathfinder's intake system. Figure with 70k miles a throttle body cleaning is in order.

Apparently coolant flows through the throttle body. Can anyone tell me why this is? Poor man's intercooler?

Coolant is hot.

It may be during the winter months, it could freeze, resulting in a stuck throttle plate, so the coolant flowing through it thaws it.

On my Maxima, I have the lines barbed and basically by-passing the TB the way we do the radiator on here.

My winters aren't that harsh, -10ºF is the coldest and have yet to have a problem.

I might do that. It seems that heating the intake air is not doing me any favors in the performance department

ive done tb bypass on all of my cars. its just one of the small free mods i have done. not sure how much it helps but it has never hurt anything.

Because I'm too lazy to do the math myself I turned to Google:

http://forum.mazda6club.com/engine-driv ... ypass.html

There's no real engineering reason to do this...

Why would anybody want to bypass this, there is no gain from doing so.

staynlean wrote:Why would anybody want to bypass this, there is no gain from doing so.

Depends on what you do on your car. I'm always changing intake manifolds and TB's on my Maxima, so it helps not make a small mess every time I do that. Serves its purpose.

No plans on doing it on the Pathfinder though.

ShipFixer wrote:Because I'm too lazy to do the math myself I turned to Google:

http://forum.mazda6club.com/engine-driv ... ypass.html

There's no real engineering reason to do this...

I had an 04 Mazda 6 which I traded in for my 08 Pathfinder. I actually did that mod on my 6 and can't say if it helped or not. I was part of that forum until I traded in my 6.

volvite wrote:

ShipFixer wrote:Because I'm too lazy to do the math myself I turned to Google:

http://forum.mazda6club.com/engine-driv ... ypass.html

There's no real engineering reason to do this...

I had an 04 Mazda 6 which I traded in for my 08 Pathfinder. I actually did that mod on my 6 and can't say if it helped or not. I was part of that forum until I traded in my 6.

The predicted resulted are below what you could expect to measure - and the math that person did (while correct) doesn't compare against a throttle body that's already heated by conduction or convection in the engine room so the predictable results are probably even less than that.

People do things like this because they make intuitive sense on some level (less heat in intake air = good) but aren't aware of or take into account the full picture. Like how carburetor and throttle body icing due to changes in temperature, humidity and velocity/pressure in the intake tract was a rare but possible problem regardless of where you live.

My personal favorites are oil myths and engine break in myths, believed widely by all. Do this, don't do that, run it hard, run it easy, this many miles, etc. The funny part is that none of it matters since modern plateau-honed cylinders experience 80% of their lifetime wear in the first 21 minutes or so of life and are well beyond "broken in" sometimes before being installed in whatever they'll power...which is why each theory always "works." The truth was written in textbooks starting in the 50's and closed out with SAE journals no later than the 80's, and yet there's all sorts of ideas out there in garages and the interwebz...

Next favorite is airbox mods for "smoothing" airflow. Before a pleated paper filter and away from surface boundaries :-/

Not everything engineers do is smart (like the cam chain tensioner debacle) but there's typically some reason for most things. Sometimes the rationale behind those things (like EPA controls) are well understood an you know what you're doing/undoing, other times it's hard to say.