Intake Manifold Coolant Bypass
By: MustardCat
Used some good info from Bobnova too.
(From: http://www.preludepower.com/forums/showthread.php?t=249458)

Link to this page:

 

 

Basics:

Q: What's this mod do anyway's?
A: Bypasses the coolant going to the TB, FIV, and / or, EACV.

Q: Hey, WTF! Don't you need that stuff?!
A: Yes and no, depends how you use the car.

Q: Well Mr. Smartypants, supposing I did this, what are some of the benefits?
A:
1. Lower intake manifold temps, no /
less hot coolant running though it.
2. Fewer coolant lines running around, less chance of one leaking / breaking.
3. Less chance of "bouncy idle", often caused by the FIV or EACV, cut them out of the loop and the idle is controlled only by the idle adjust screw.
4. "Cleaner" look, subjective, depends how much time you want to devote to the project.

 

For reference:
IM = Intake manifold
TB = Throttle body
FIV = Fast idle valve (On back side of IM, near TB)
EACV = Electronic air control valve (Front center of IM)

Here is a diagram that shows the general locations of the components and how the stock hoses are routed. Note that the water pipe is actually under the IM next to the block:


3 components you can bypass, you can do any or all of them, so I'm going to list the pros and cons of each.

Throttle Body:
The coolant lines going to the TB are basically useless for 99% of 3G owners, this mod should be done by most owners whenever you get the chance.

Pros:
1. Lower intake air temps.
2. Removing the TB is much quicker and easier, since you don't have to mess with those damn coolant lines.

Cons:
1. There is a remote possibility in very cold climates that the flapper in the TB could get frozen shut. These lines are basicly a throwback to the old carbeueration days when this actually happened, new Hondas have elminated the TB coolant lines completely.


Fast Idle Valve:
The FIV raises the idle when the motor is cold, by allowing additional air to bypass the TB. At 80F and below it's fully open, once the coolant hits 140F it's completely closed.

Pros:
1. Bolted right onto the IM it transfers heat from the coolant into the IM, raising intake temps. Bypassing it lowers temps.
2. Can contribute to a "bouncy idle" condition, and bypassing it will cut it out of the loop and eliminate that possibility.

Cons:
1. May cause the car to idle low when the motor is cold, not a good idea to remove it in very cold climates if your car is a daily driver.


Electronic Air Control Valve:
The EACV is what the ECU primarily uses to control the idle. It's mostly used to boost the idle when the P/S system is being used and when you turn on the A/C. Additionally if the ECU detects a low-idle when the coolant is still cold it will use the EACV to boost the idle in place of the FIV.

Pros:
1. Bolted right onto the IM it transfers heat from the coolant into the IM, raising intake temps. Bypassing it lowers temps.
2. Can contribute to a "bouncy idle" condition, and bypassing it will cut it out of the loop and eliminate that possibility.

Cons:
1. May cause low-idle problems on a car with P/S and the A/C turned on. (Ok with just P/S.)


Bypassing all three:

Pros:
1. Lower intake manifold temps, see this page for specific numbers.
2. Idle is now mechanically controlled, by the idle adjust screw on the TB. Very smooth and consistent idle once the car is warmed, quick and easy to adjust as well.
3. Very few of those little coolant lines running everywhere.
4. More room to work around IM, fuel rail, injectors.
5. Less work to remove TB, IM or parts of IM.
6. Looks better, depending how you do it.

Cons:
1. The motor will idle badly, maybe not at all when the motor is cold. You may need to hold the RPM around 2000 with the gas pedal for a minute when you first start the car.
2. No idle boost for P/S or A/C. P/S seems to work fine without it on my car, but I don't know about A/C.
3. Not recommended for daily drivers.


Ok to do all three the quick and easy way here's a little diagram:

You cap off the hoses coming out of the water pipe and make solid gaskets to go between the IM and FIV+EACV.

If you want to remove the FIV and EACV from the manifold completely you can do what I did on my manifold. (Scroll 3/4 way down, looks better IMO.)

One thing you need to remember is to keep the electrical plug on the EACV plugged in, even if it's blocked off. Unplugging it will cause a check engine light and drivability problems.

 

I want lower temps but don't want a big sacrifice in drivability!

Here's the more daily driver friendly version. Keeping the EACV functional should avoid any problems with cold idle, P/S, and A/C.

 

 

 

 

Here are some pics of how I did it on my 88 Accord. (Almost identical as the lude.) I kept the EACV functional because this is a daily driven car:

Here's how I blocked them off on my lude, I tapped the holes and screwed brass plugs in: