coolant bypass - Honda Prelude Forum

MNludeDVR · 05-19-2002, 02:02 AM

i did a search for it..but what's a coolant bypass mod?

MNludeDVR · 05-19-2002, 02:03 AM

sorry, i meant i did a search and couldn't find anything

marcucci · 05-20-2002, 06:56 AM

From the factory the coolant flows through the throttle body and idle air control valve, to heat the manifold. This is really only useful in extremely cold climates, to help prevent icing in winter. The bypass is rerouting the lines to prevent the coolant from heating these items.

The only issue is a thermo valve in the throttle body that, when bypassed, will make the idle oscillate from normal to about 2000 rpms, then back down... when cold.

93PreludeS · 05-20-2002, 07:02 AM

its also a pretty useless mod, it just makes your car run in fast idle mode longer.. the difference in temps is not enough to make any kind've power in your car.. .01 hp i think would be possible

..

jpprelude · 05-20-2002, 03:23 PM

It isn't a good idea if you plan to drive in our cold MN winters. You get a goofy bouncing idle until the car warms up.

PatLude · 05-20-2002, 05:28 PM

Well,

Re-routing the coolant lines that normally heat the intake was BY FAR the greatest mod I ever did. I never felt so much gain from a mod when I compared versus my cat-back exhaust and CAI gains that were not so easy to feel...

After rerouting the collant lines........ To avoid strange Idle running, you just need to plug the LOWER hole inside the Throttle body. This will stop the air from bypassing the throttle body via the Fast Idle thermo Valve. Simple. Easy. Effective. You will noticed a lower Idle RPM (around 1000RPM) when the engine is cold compared to the normal. BTW, I had to remove the TB in order to plug the hole in a clean way. And, the TB is very easy to remove...

Note : Don't plug the upper hole since it's the throttle air bypass for the IAC valve (Idle Air Control). The IAC Valve changes the amount of air bypassing the throttle body in response to a current signal from the ECM in order to maintain the proper idle speed.

93PreludeS · 05-20-2002, 06:14 PM

well, i think its useless pretty much.. no one has dyno'd the mod, and i dont think it creates any power.. have you got any like concrete type proof of it improving? just wondering since i did it a while back, went to stock again,, and same result

PatLude · 05-21-2002, 10:54 AM

Well,

Here is a little story : A member of the MPC once noticed that his lude was very slow. Something was definitely wrong with his car since it wasn't pulling at all. After a lot of investigation, they found out the Fast Idle Thermo Valve (FITV) was the problem when someone noticed that the Intake Manifold was red hot.... The FITV was not closing at all, always allowing the coolant to run through the Intake Manifold......... Resulting in an higher Intake Manifold temperature than the normal.

So, if a hotter manifold intake temperature has such an negative impact on the performance, I easily assume that a colder intake manifold would have a postive impact on the performance.

And since my lude also become slow during hot traffic driving because of the engine bay getting real hot, I definitely saw bad (or good) impact on performance when the air temperature changes.

If the mod doesn't work, a CAI doesn't work neither...

My opinion

vtecprelude · 05-21-2002, 11:36 AM

I did this mod and also bypassed the IAC valve. I took out the TB and removed the 3 screws that holds the part where the coolent flows and in place of that I cut out a piece of rubber and laid it flat against the lower part of the TB and than screwed the piece taken out over it. This blocked all the holes that are in there. I no longer get bouncy idle.

MechEng · 05-21-2002, 11:50 AM

I think this mod has potential. I've tried the Flapper Mod and I didn't like it cuz it I lost torque. The Fuel Pressure Mod gained power but caused an increase in fuel consumption.
This one I'll try next week.