coolant bypass the throttle body??

[zip]

Bypassing the IAC keeps the spring inside the IAC from freezing in cold air climates and increases the spring's (k) resistance to the solenoid as coolant temps increases. But I think the coolant is mainly to keep icing off the spring/plunger setup. I've had the IACV bypassed for a couple of months now w/out any detrimental effects to drivability. But of course I live by the coast in California, where the weather seldomly reaches freezing. Combined w/ the TB bypass, the IAC coolant bypass reduces heatsoak considerably. Hondata has some comments about bypassing the TB and IAC coolant lines here: http://forums.clubsi.com/ubb/Forum12/HTML/005239.html http://forums.clubsi.com/ubb/Forum12/HTML/005386.html

Although Hondata is plugging there phenolic spacer it's still food for thought that he still bypasses the coolant line for the IAC and TB for reduced heat soak gains.


The two photos below show the internal workings of the IAC. It's basically a solenoid and spring combo w/ the ECU controlling it's duty cycle (basically like a solenoid regulating air flow for an electronic boost controller). The IAC is not only used for fast idle but also keeps the revs up when you let of the gas abruptly to prevent the engine from stalling out and increases air flow into the engine when power draining accessories are activated, i.e. headlights, power steering, AC...etc. The increased air flow helps the engine compensate for the increased load.




Here's the area that the coolant actually warms up.



I actually proposed this coolant bypass mod along w/ the TB bypass mod months ago but most weren't too clear on what I was attempting to do: http://www.hostboard.com/ubb/Forum40/HTML/004058.html

For a relatively easy mod, I can state that after running these two bypass modifications for the last couple of months that they indeed reduce intake charge and intake manifold heat soak times significantly. However, members that live in colder climates should we weary about this mod come winter time.

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Mods

[This message has been edited by zip (edited September 17, 2001).]

[Holden]

Since I have my engine bay cleaned out to get at the rear motor mount and put an oil cooler in, (intake, fuel line, throttle cable bracket, upper rad. hose, coolant line from head to TB are all removed currently), I believe I will try this mod. (Bypassing both TB and IACTV??!@VACTFE!#@$)

I do live in a cold place though. What will happen to me if I drive like this in, say, 40 degree humid weather (a typical nighttime except for late-June till early August)?

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Greg Holden
96 GSR, JSRC @10psi, All the Goodies!
Best 1/4 ==> 13.937 @ 101.41mph (at 6psi)
My JRSC Install Site

[rjaffey]

OK, here are some rather unscientific results:

I clamped off the coolant line running to the Fast Idle Thermo Valve and went driving (boosting perhaps 5% of the time) for an hour. This effectively stopped coolant from flowing through both valves.

I didn't have time to take before and after temperature measurements (I'll do that at some point and post results), but here are some observations and comments:

- The outside air temperature was about 55 degrees.

- After the coolant temperature gauge began to register above mininum, the idle speed began to drop a bit. After releasing the throttle the idle speed tended stick around 1500RPM for a few seconds and then drop to 1000RPM where it was not as stable as normal. I attribute these two things to what I proposed before, that the IACV is operating outside of it's normal range and therefore not having the charactoristics the ECU "expects". It might even be shutting all the way. This affects how well the ECU can accomodate changing accessory loads and implement the "dashpot" behavior Zip mentioned.

- After about 10 minutes of driving, I popped the hood and felt the blower, TB, Fast Idle Thermo Valve, IACV and coolant running from the IACV to the main water pipe; not the one I clamped off. The components and coolant line were still cool to the touch, though warmer than ambient. The other coolant lines were already hot.

- The idle stayed above normal for about 15 to 20 minutes.

- After about somewhere between 20 and 30 minutes (I can't tell exactly when as I was taking a non-stop cruise on Lake Shore Drive for about 10 minutes), the idle speed dropped to normal and stayed much more consistant with respect to accessory load. The dashpot behavior was normal as well. I popped the hood and felt component temps again. I found that everything had warmed up a bit, but the throttle body and air valves were nowhere near as hot as other coolant lines. They were just warm, perhaps 90-100F. The specs indicate that the Fast Idle Thermo Valve closes completely at 86F, so I conclude that after a period of time, it absorbed enough heat to close without coolant passing through it, though it might require the valve to be filled with coolant rather than air in order to maximize heat transfer from its casting into its "thermowax plunger". Another argument for a shutoff rather than completely disconnecting the Fast Idle Thermo Valve.

- The coolant line from the IACV to the main water pipe was about as warm as everything else, so I conclude that there's no need for two shutoff valves. I'll verify this when I take some before and after temperature readings.

- The idle would likely stay faster and more erratic than normal for a longer period if not indefinitely were the ambient air temp colder, because it would take longer for the Fast Idle Thermo Valve to absorb heat from surrounding components. It may never reach 86F if the surrounding air is too cold. Of course this is not a problem, as I'd open the shutoff valve and allow the coolant to flow normally were the outside temp much lower than it was last night.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>increases the spring's (k) resistance to the solenoid<HR></BLOCKQUOTE>

Zip, you're going to have to explain this one.

[This message has been edited by rjaffey (edited May 25, 2001).]

[Holden]

Rafe: So what you're saying is that one shutoff valve in the hose between the head and the TB will accomplish the goal and allow us cold weather guys to switch back to normal easily. Right?

Thanks,

Greg

[zip]

Rjaffey, I think the SI and GSR coolant setups are different, since I'm positive that I've never seen the fast idle thermo valve you've mentioned. Here's a pict of an SI (typeR) big bore TB:

As you can see, there isn't an attachment for the fast idle valve you mentioned on your post.


The coolant merely just goes in and out of the TB and onto the IAC coolant ports I pictured above. From the IAC, the coolant lines end at the main water pipe. So to reiterate, the coolant flows from the head, to the TB, then to the IAC, and back to the main water pipe. I basically just connected the coolant hose from the head to the main water pipe, thereby effectively bypassing the IAC and TB from the coolant flow. Essentially, coolant flows freely among these components w/out a restriction imposed by any valve.

The spring resistance I mentioned is just an observation. Springs tend to increase in resistance as they warm up. I figure that Honda took this into account when designing the IAC operation at normal operating temps. As the coolant warms up the whole IAC assembly, the spring inside will tend to warm up since it's physically in contact w/ the IAC body. The IAC is left closed until extra air is needed by the engine. When the spring has reached its normal operating temps it "dampens" the plunger that the solenoid pulls against when the ECU sends the pulse signal to the IAC. Since the ECU sends pulse widths rather than a constant signal to the IAC, I think the spring helps keep the IAC open a tad longer.

When I bypassed the IAC I noticed that idle speed fluctuated just a little from normal (nothing drastic) since the spring wasn't aiding in keeping the IAC valve opened longer. Since Honda ECU's are pretty smart, the ECU would realize that the IAC wasn't being kept open w/ the preprogrammed pulse signal and it would instantly stabilize the idle w/ a new duty cycle. Just an observation.

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Mods

[This message has been edited by zip (edited September 17, 2001).]

[johnyew]

Here's how my TB bypass expereince was:
I drive a JDM 4G Prelude VTEC.
At first, I only bypassed the coolant lines to the FITV and had a piece of thin metal plate to block it off from the TB. The hunting idle problem surfaced after a few days. So, I reconnected all the coolant lines back again and removed the metal plate. After reading about this problem in forums and some further suggestions, I went back at it again and this time, in addition to the FITV coolant lines and metal plate, I also bypassed the coolant lines to the IACV. What I ended up doing was simply connecting together the coolant fittings at the thermostat housing that was coolant suply/return point to the FITV and IACV. It's been almost a year and a half now since that mod and have never encountered the 'hunting idle problem'.

[rjaffey]

Zip,

Thanks for the clarification. Are you sure the IACV is receiving pulses rather than a constant signal?

Greg,

I think that's correct based on my testing last night. It's certainly worth trying out. It's clean, simple, and reverseable; the way I like all of my mods.

[zip]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rjaffey:
Zip,

Thanks for the clarification. Are you sure the IACV is receiving pulses rather than a constant signal?

Greg,

I think that's correct based on my testing last night. It's certainly worth trying out. It's clean, simple, and reverseable; the way I like all of my mods.<HR></BLOCKQUOTE>

I'm sure the IAC receives pulses because it regulates incoming air to the motor which means it has to be pulse width controlled. The Helm also states that it's duty controlled hence pulses are used to control the solenoid.

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Mods

[Import Tuner]

Guys, I've found that with any ACV (Air Control Valve) that has coolant lines into it is of the thermal wax variety...

What that means is if the valve is in a cold condition (enough to solidify wax) then your bypass will be open, regardless of weather you have manifold vacumm or not...

The coolant lines heat the wax, that in turn allows the manifold vacumm to close the bypass air, because the wax is now a liquid...

If you eliminate / bypass the coolant lines, than heat soak will be your only means of melting the wax...
(Hence what Rafe said, "it seems to take longer than what the ECU expects")...

If you just want to bypass a coolant line that runs under some throttle body's and just goes in and out you can...
Just don't be surprised if your cruise control doesn't seem to disengage in lower ambient temps...

As for bypassing

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Donny
Import Specialty Automotive
(253) 473-2606

[Import Tuner]

Guys, I've found that with any ACV (Air Control Valve) that has coolant lines into it, is of the thermal wax variety...

What that means is if the valve is in a cold condition (enough to solidify wax) then your bypass will be open, regardless of weather you have manifold vacumm or not...

The coolant lines heat the wax, that in turn allows the manifold vacumm to close the bypass air, because the wax is now a liquid...

If you eliminate / bypass the coolant lines, than heat soak will be your only means of melting the wax...
(Hence what Rafe said, "it seems to take longer than what the ECU expects")...

If you just want to bypass a coolant line that runs under some throttle body's and just goes in and out you can...
Just don't be surprised if your cruise control doesn't seem to disengage in lower ambient temps...

As for bypassing

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Donny
Import Specialty Automotive
(253) 473-2606