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 Running without coolant to Throttle body/plenum? 
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Post Re: Running without coolant to Throttle body/plenum?
At what temperature and humidity does the idea of your throttle plate "sticking open" due to freezing become a likely occurrence...? Maybe a long haul with cruise control on, without ever moving the plate from one static position, with high humidity...

I'm pretty sure the spring on the throttle linkage would still be strong enough to overcome a little bit of thin ice buildup... Surely you wouldn't see enough buildup to cause an accident?

I may be entirely misunderstanding what you are trying to say, but it doesn't make sense to me from this perspective...

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January 22 2013, 12:09 AM
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Post Re: Running without coolant to Throttle body/plenum?
Pressure drop in pascals is roughly equivalent to the temperature drop in kelvin.

So you'd need a decently cool day.

The main reason this doesn't happen to anyone is because of the other sources of heat in the bay, but I'm sure there are more free-flowing older engine bays where this was more of a problem (carbs had it worse too).... Just good practice Mazda carried on; if their reason wasn't entirely to use the simple wax valve, this was a bonus benefit.

Methinks it doesn't make sense to you 'cause you haven't done much thermo or fluid dynamics.

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January 22 2013, 1:30 AM
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Post Re: Running without coolant to Throttle body/plenum?
What is decently cool? Colder than I see in Western Oregon? :wink:


Ryan wrote:
Methinks it doesn't make sense to you 'cause you haven't done much thermo or fluid dynamics.


Now that I won't deny. :lol:

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January 22 2013, 2:57 AM
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Post Re: Running without coolant to Throttle body/plenum?
I unno man, 5-10 centigrade? just shooting in the dark for numbers. run a pitot tube to the throttle and I could let you know when it might become a concern :P

If you don't believe me, just google it... carburetors have it worse than us because they make efficient venturis on purpose. Also airplanes have it bad.

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January 22 2013, 9:54 AM
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Post Re: Running without coolant to Throttle body/plenum?
Ryan wrote:

This is wrong. Air always has a moisture content, called humidity. This humidity is what condenses in the pressure drop across the venturi. Has nothing to do with liquid water. Has nothing to do with still condensation overnight.

Because thermodynamics.



New science meme?!! huh huh :)

Carb ice is scary and is one of the number one reasons people crash helicopters. Everyone removes and blocks the IAC and I think it is kind of dumb. That is why my BP still has it intact. My stand alone does not have one, but I bought an inline valve that will serve the same function and increase idle based off of intake temperature. An increase in cost for a good cause IMO.

Blake I would recommend looking up carburetor icing and you will find a lot on the subject and temps at which it forms. Generally it is not an issue in an automobile because of the engine compartment that we have, but it can and I am sure it has happened. It would be more likely to happen on a longer drive but it really does not take long to form. In flying rotor-craft they are subjected to this condition even in the summer.

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January 22 2013, 1:11 PM
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Post Re: Running without coolant to Throttle body/plenum?
Ryan wrote:
I unno man, 5-10 centigrade? just shooting in the dark for numbers. run a pitot tube to the throttle and I could let you know when it might become a concern :P

If you don't believe me, just google it... carburetors have it worse than us because they make efficient venturis on purpose. Also airplanes have it bad.


I believe you, but I've never seen nor heard it this problem with EFI engines.
Airplanes fly pretty high up there, and correct me if I'm wrong, the air is a little cooler up there? :lol: The same applies to helicopters.

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'92 GS 5 spd - Straightneck KL, 67mm TB, MegaSquirt, Coilpacks, 5 lugs, Speed6 brakes, FD wheels, wiretuck, progressive coilovers, shorty headers w/ custom collector, AEM WB, 2.5" straight, Borla XS
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January 22 2013, 4:02 PM
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Post Re: Running without coolant to Throttle body/plenum?
Again, it's not about the temperature of the air so much as the change in pressure as it enters the engine.

Honestly I don't think icing would be a common problem for most of us regardless of climate. I think the magnitude of the effect of having the coolant lines disconnected from the TB is going to depend on a lot of other tuning factors. The Idle Air Screw, the length and diameter of your intake, how clean or dirty is your TB...all these things will impact how the TB performs without that warming circuit.

I think that's why the results vary from car to car. My TB is really clean and everything was just reset and I imagine it would idle ok in summer, but right now it's -12 to -20ºC most mornings and without the coolant to heat up that wax the idle would never come down.

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January 22 2013, 4:17 PM
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Post Re: Running without coolant to Throttle body/plenum?
Blake - I am correcting you you are wrong. Altitude and temperature have nothing to do with it. Again look up carb icing and thermodynamics.

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January 22 2013, 5:07 PM
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Post Re: Running without coolant to Throttle body/plenum?
I'm not sure how to even wrap my head around this.
Is it true or false that water takes less time to freeze when in a -20 degree environment, vs a 20 degree environment?

I don't mind being corrected, I would just people to explain where my mistake occurred. :/

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'92 GS 5 spd - Straightneck KL, 67mm TB, MegaSquirt, Coilpacks, 5 lugs, Speed6 brakes, FD wheels, wiretuck, progressive coilovers, shorty headers w/ custom collector, AEM WB, 2.5" straight, Borla XS
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January 22 2013, 6:46 PM
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Post Re: Running without coolant to Throttle body/plenum?
Sorry Sam for jacking your thread :oops:


It is a condition relative to the humidity and dew point and temp plays a much smaller role than you would think. So for us here in the PNW we have this issue. Generally with EFI your chance of carb ice is lessened. However if you run without the coolant lines into the TB this increases your chances of this happening. As of right now out of PAE airport in Everett we are at 6deg C and -02 Dewpoint

Go here http://www.atsb.gov.au/publications/2009/carburettor-icing.aspx

Image

Image

This image is actually in one of my books.
Image

A quick search I found several cars and motorcycles that have this issue even with EFI.

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January 22 2013, 8:11 PM
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Post Re: Running without coolant to Throttle body/plenum?
Here is the Cole's notes version of the science...

Air contains moisture. Warmer air is able to hold more moisture than colder air. This is why water condenses on windows when it's cooler outside than it is inside. Warm moist air hits the cool glass, temp goes down, it can't hold the moisture and the water clings to the glass...or whatever cool surface it is in contact with. But it doesn't have to be a hot air vs. cold surface scenario. This would also happen in a hot air vs less hot surface situation. You already understand this concept.

When you compress air...it gets warmer. Actually when you compress anything it gets warmer but the effect is more obvious in gases because they are so readily compressible. Here's the kicker...the reverse is also true. When a gas expands it cools. Did you ever see propane being released from a bottle? The mosture freezes because it is expending rapidly from the compressed state to atmospheric pressure. The same thing happens, though less dramatically when air at atmospheric pressure enters an area of lower pressure. expansion occurs, temperature drops. If the change in pressure is high the change in temperature will also be great.

With respect to your engine. The air outside the TB plate is at ATM pressure. The air inside the TB plate is at a mild vacuum because the engine is sucking as hard as it can and only so much air can get in at a time...air enters the intake, pressure drops, it expands...temperature drops. But at the same time, it the right conditions, condensation can be occuring on the surfaces of the TB.

These two conditions can cause ice to form even when it's above freezing temps outside. Although it can happen without condensation if the change in pressure is great enough. I don't know much about aircraft engines but my guess is they suck pretty hard.

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January 22 2013, 9:34 PM
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Post Re: Running without coolant to Throttle body/plenum?
There is some good information about the coolant side of the IAC systems on the KL's, but there is some miss information about the stepper motor and how the whole IAC system works as a unit...

The coolant side of the IAC is for cold start idle control... As mentioned its used to increase idle during cold start acting much like an old carburetor choke... It doesn't take long for the coolant passing threw the throttle body to warm up causing the wax pellet to move and lowering your idle down...

1 bit of terminology you need to understand before I continue... Base idle... This is the idle that is set, with no accessories turned on, the car at operating temperature, cooling fan off, ac fan off, no steering movements, base timing set correctly, idling in neutral or park..

Ok, the stepper motor side of the IAC system... This is whats known as an Idle up solenoid... It has little to no function at all in controlling base idle when everything is working properly, and base idle is set correctly.. Its function is to keep the idle smooth, and keep the motor from stalling when various accessories are turned on and off, causing various different loads to be put on the motor... This would include things like turning you heater fan on, the cooling fan turning on, your ac kicking in, turning your steering wheel while at an idle, shifting between park, drive, reverse ect on an automatic car.. It will also have some affects during light throttle cursing as well to avoid a surging feeling when the cooling fan is turned on, or ac kicks in ect...

Base idle is set by adjusting the throttle plate with the motor warmed up idling in neutral/park, no load and the car set in diagnostics mode..Once you get the idle set or anytime you play with the throttle plates you have to adjust the tps.. The 4th wire on the tps is an idle command switch... The computer uses this as an input to know when the motor should be idling....

This system of idle control is used in many different older (early 80s - mid 90s) cars/trucks/manufactures.... When you get away from 4 wire tps, and coolant controlled cold idle valves, then whole process is different..


January 22 2013, 10:22 PM
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Post Re: Running without coolant to Throttle body/plenum?
wytbishop wrote:
With respect to your engine. The air outside the TB plate is at ATM pressure. The air inside the TB plate is at a mild vacuum because the engine is sucking as hard as it can and only so much air can get in at a time...air enters the intake, pressure drops, it expands...temperature drops. But at the same time, it the right conditions, condensation can be occuring on the surfaces of the TB.


Oh, now THAT makes sense! :o I didn't think about it so much in terms of pressure as temperature. This would explain why this may occur in warmer climates, right?

It would also lead me to believe the "increase" in risk at high altitude is relative to air lower PRESSURE, and not temperature.

Am I going in the right direction now? :D

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'92 GS 5 spd - Straightneck KL, 67mm TB, MegaSquirt, Coilpacks, 5 lugs, Speed6 brakes, FD wheels, wiretuck, progressive coilovers, shorty headers w/ custom collector, AEM WB, 2.5" straight, Borla XS
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January 23 2013, 2:44 AM
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Post Re: Running without coolant to Throttle body/plenum?
It's all about pressure CHANGE, not ambient pressure. But yes this is actually....I would guess...a bigger problem at temperatures above freezing because air at or around 0ºC has very little moisture in it.

CrazyCanadian's information is much more helpful to me though. Understanding how that system works is very helpful.

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93' GS SE, the Black Beast, the former love of my life...soon to be gutted and crushed.
94' GS, black on black, now in several small pieces...and one large crushed piece.
2007 Mazda3 GT Sport --- super fun
2004 Honda RC51 --- Lost forever to some theavin' bastard
My Worklog
My feedback thread
Never attribute to malice that which can be adequately explained by stupidity.


January 23 2013, 10:40 AM
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