coolant passage in the throttle body
why? what for? i really can't think of a reason why there is a coolant inlet and an outlet in the throttle body. I thought they were vacuum lines but coolant spilled over when i pulled the line.
Anyone care to explain? Mine is throttle-by-wire if that matters.
Re: coolant passage in the throttle body
<div class='quotetop'>QUOTE(9G)</div><div class='quotemain'>why? what for? i really can't think of a reason why there is a coolant inlet and an outlet in the throttle body. I thought they were vacuum lines but coolant spilled over when i pulled the line. Â*
Anyone care to explain? Mine is throttle-by-wire if that matters.</div>
coolant goes to mitsubishi throttle bodies because of the fast idle air valve.
FIAV
ever notice that when you start the car(when coolant is cold i.e. in the morning or after sitting for an hour)
your idle is high, 1200-1400
this is because of thre fiav.
THE WHY
:arrow: when your engine is cold it draws a weaker vaccum which makes it more difficult to sustain a typical idle.
:arrow: when your oil is cold it operates at higher pressures. it is very thick and harder to pump. this puts a load on your oil pump and has a similar effect to turning on the a/c compressor, or cutting the wheel and the power steering pressure causig the engine speed to drop(just more drag on the crank) _when my oil temp is 50 degrees at startup my oil pressure is 65 psi at idle. then when my oil temp is up to 185 the oil pressure has dropped to around 15 psi at idle(oil is more fluid and thinner)
since the crank turns the oil pump, the engine can stall or idle very low and rough because of the extra load under low vaccum
:arrow: the higher idle allows your coolant to warm up faster aiding in satisfaction and comfort of the driver.
:arrow: the higher idle aids in oxygen sensor warm up(in tandem with the built in o2 sensor heater) increasing fuel efficiency and lowering emmissions by allowing it to reach closed loop mode sooner.
:arrow: the higher idle aids in warm up of the catelytic converter helping to reduce emmissions.
:arrow: the higher idle allows the oil, coolant, and mechanical components of the engine to reach operating temperatures sooner.
the HOW
inside the throttle body in the FIAV there is a wax pellet. the coolant circulateds past this pellet and a corresponding mechanism. when the coolant is lower than a desired temp the mechanism opens a passage that bypasses the throttlebody. this allows more air to get into the engine at closed throttle effecdtivly raising the engine speed.(this is your cold high idle)
when the coolant is warmed up(i think around 180 degrees) the wax pellet melts and the mechanism closes off the passage. then your idle returns to its normal state, and is completely under control of your idle air controller.
this method is just a very simple, very reliable, and very inexpensive mechanical method of combatting a cold motor. its been done this way for years.
another method to get the same results.
since the ecu can see the coolant temperature. it is going to know when the idle needs to be high and when it needs to be restored to normal( the obd2 ecu's can check that the cat is warmed up, that the o2's are warmed up, even what tempurature the coolant is)
so other vehicle manufacturers(not all) achieve the fast idle mode through an electronically controlled solenoid. when the engine is cold the solenoid ids open, when its warm the ecu closes the solenoid.
very simple. the solenoid controls the air that is bypassing the throttle plate.
however this is more expensive, solenoids are not cheap especially when compared to the cost of a foot of coolant hose.
also solenoids wear out/fail.
so there you have it. hope that answered your question.
here is a pic of the fiav and its passages
http://www.ffwdconnection.com/fiav.gif
the passages and spring on the left are a part of the fiav system. the passages on the right are for the iac.