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#4331916 - 02/17/17 11:23 AM Re: Why are IAC Valves Heated? [Re: SHOZ]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 18154
Loc: Sunny Florida
Originally Posted By: SHOZ
Almost all throttle bodies are heated by the coolant. First mod I do is to bypass the coolant hoses.


Some things never change. In my old cars we often blocked the crossover in the intake that was filled with coolant to cool the intake charge a bit.

I had a drag car (400 Firebird) that would actually get the intake pretty cold under certain conditions, cold enough to help power a bit...
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#4331920 - 02/17/17 11:29 AM Re: Why are IAC Valves Heated? [Re: artbuc]
nthach Offline


Registered: 01/02/04
Posts: 2444
Loc: California
Old Mercedes or VWs with Bosch K/KE-Jetronic didn't have heated IAC valves nor heated throttle bodies(at least on VWs, the Mercedes K-Jet setups had the throttle body downstream from the fuel distributor/air flow measuring mechanism).

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#4332071 - 02/17/17 01:58 PM Re: Why are IAC Valves Heated? [Re: artbuc]
Kawiguy454 Offline


Registered: 06/01/15
Posts: 505
Loc: Arizona
Originally Posted By: artbuc
Originally Posted By: Tegger
Originally Posted By: Linctex
during the course of extreme temperature testing, someone felt it helped drivability in some way

It's meant to counter the icing that results from the venturi effect, something that can manifest at ambient temperatures well above freezing.


This is what I believe.


+1 icing ...My honda foreman 400 had an electric plug in the carb to combat icing and the wife's carburated Yamaha had the coolant plumbing. Remember Gasahol can absorb/carry water...

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#4332076 - 02/17/17 02:04 PM Re: Why are IAC Valves Heated? [Re: artbuc]
SHOZ Offline


Registered: 06/28/03
Posts: 4359
Loc: Illinois
The only time I have personally experienced this is back in the early 80's I had a Triumph TR7 with 2 Stromberg side drafts. No coolant hoses but did have the exhaust manifold heater tube and regulator on it for the air cleaner. Which I had disconnected.

So driving down the highway once cold foggy morning the car kept going slower and slower. I finally stopped and figured it out. Just sitting with the engine off heated the sliders up enough to break the frost.

I also put a temp probe just in front of the throttle body on my Gen Coupe once and saw temps below freezing at about 40F, this was when the throttle was closed at high rpm.
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#4332097 - 02/17/17 02:30 PM Re: Why are IAC Valves Heated? [Re: SHOZ]
artbuc Offline


Registered: 12/02/05
Posts: 950
Loc: West Chester, PA
Originally Posted By: SHOZ
The only time I have personally experienced this is back in the early 80's I had a Triumph TR7 with 2 Stromberg side drafts. No coolant hoses but did have the exhaust manifold heater tube and regulator on it for the air cleaner. Which I had disconnected.

So driving down the highway once cold foggy morning the car kept going slower and slower. I finally stopped and figured it out. Just sitting with the engine off heated the sliders up enough to break the frost.

I also put a temp probe just in front of the throttle body on my Gen Coupe once and saw temps below freezing at about 40F, this was when the throttle was closed at high rpm.


Bought a brand spankin' new TR6 in 1974. Loved that car but it was an electrical/mechanical cluster [censored]! White with blue interior. Nice memory.


Edited by Bill in Utah (02/18/17 02:12 AM)
Edit Reason: Bypassing the censor

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#4332141 - 02/17/17 03:14 PM Re: Why are IAC Valves Heated? [Re: artbuc]
artificialist Offline


Registered: 09/23/07
Posts: 8414
Loc: Florida
My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.
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#4332214 - 02/17/17 04:49 PM Re: Why are IAC Valves Heated? [Re: artificialist]
artbuc Offline


Registered: 12/02/05
Posts: 950
Loc: West Chester, PA
Originally Posted By: artificialist
My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.


What about the IAC valve?

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#4332380 - 02/17/17 07:51 PM Re: Why are IAC Valves Heated? [Re: artbuc]
artificialist Offline


Registered: 09/23/07
Posts: 8414
Loc: Florida
Originally Posted By: artbuc
Originally Posted By: artificialist
My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.


What about the IAC valve?


Heating the IAC valve would still heat the air fuel mixture at idle to reduce smog at low temperatures.
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#4332589 - 02/18/17 05:53 AM Re: Why are IAC Valves Heated? [Re: KrisZ]
Merkava_4 Offline


Registered: 01/30/07
Posts: 15495
Loc: Clovis, CA
Originally Posted By: KrisZ
Most of the time, this emotionally driven behavior causes more harm than good.


LOL

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#4335691 - 02/21/17 11:33 AM Re: Why are IAC Valves Heated? [Re: artbuc]
ARCOgraphite Offline


Registered: 05/17/09
Posts: 10616
Loc: N.H, U.S.A.
My 8HP Tecumseh Snow king engine has a heated carb I think.
On most engine, There is not enough surface area in the TB to provide significant heating of the air column. I would most assuredly say it is to prevent icing at the tb at idle and light throttle where there is a lot of gas cooling due to a "refrigeration cycle" occurring around the throttle. The IAC is usually nearby, and the IAC is a throttle bypass subject to freezing as is the main throttle.
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