Throttle Body Coolant Bypass

[4WRXter]

I don't have my camera to take pics, but....On the bottom of the throttle body there are 2 small hoses that put engine coolant through the TB. It is supposed to help with cold starts?? I was reading on a truck forum about bypassing this to keep hot coolant out of the TB, thereby getting cooler air in to the engine. The way to bypass is to unhook the rubber hoses from the TB and get a small piece of some kind of metal tubing (BRAKE LINE?) and put that between the 2 hoses and reclamp them. Has anyone considered or done this to SOOBIES? Does it help in anyway? You could always reconnect the system for winter duty.

 

[inski]

I dont know how it will help with cold starts(coolant lines hooked up) but I think it could help with keeping the TB from icing up.

 

[4WRXter]

Inski's first paragraph is exactly what I was thinking. Jury is out on whether I will try it. A lot of the guys on the truck forum had done it. A little research is in order.

 

[SUBARUDE]

they sell the kit to do this on ebay real cheap for subaru

 

[Ferrari]

I just saw this the other day........

Here! http://www.northursalia.com/modifications/drivetrain/bypass/bypass.html

Hope that helps!

 

[4WRXter]

Thanks Jamie. I'm looking for anyone who has done it, and the results of the mod. Even theoretical results from knowledgeable folks are accepted.

 

[gearsoup]

I had the bypass on my swap, but that was mostly out of laziness and stuff. The hoses that I pulled off of the 1.8 block were the wrong size for the ports on the 2.5 block. I ended up blocking them off for a month or 2. After I reconnected them, I didn't notice any changes in performance...

I'd be leary of having a sticking throttle in the winter time.....

 

[Ferrari]

I did this mod to the 4-wheeler I had. It was all performance. It made a barely noticeable diff. Until it was winter time. Than it ran like crap. You had to warm it up for 30min. to get it to idle. I never rode it in the winter but I'm guessing you'll want to drive your car in the winter. My .02, if you're gonna' do it, make it easily reversable.

 

[4WRXter]

Yeah, I sort of figured I would need to put it back for winter. I got to really thinking about the bypass a little, after my car idled a little low, and hesitated ever so slightly on launch last Thu driving to B&BS. I was a little worried about a stall at the traffic lights in L/A.

I wouldn't think the coolant in the TB would make much difference on cold start if the coolant is cold too. But what the hell do I know. I aint no engineer. I'm just a dumb ski tech, bike mech, electrician.

And I've been told you don't learn if you don't ask.

 

[Trevor723]

I did it to my car. Did it make a difference? Who knows. If you wanted to do it permanently, like I did, it sets up very nicely that you can cut off the last little bit of the hose coming out of the block and it fits perfectly to where the throttle body return line goes.

 

[inski]

I'm going to try it. North U mentioned 200+ degree coolant. Approx outside air temps at the engine are around 100 degrees, so WITHOUT 200+ degree coolant running thru the TB incoming air will be approx 100 degrees cooler, which has to be good for 'freeing up" horse power. Might have a negative effect on MPG as many HP increasers do, but we'll see.

 

[Evan]

i've done it on multiple cars before. its not noticeable, but i'm sure it helps bring down the intake charge a couple degrees.

the theory behind it is that the warm coolant will stop the moving parts in the TB from sticking in cold weather, but it never happened to me with it modded.

just take the two hoses off and connect them, or cap them off at the source, it doesn't matter to the flow pattern at all either way.

 

[LastDitchRacing]

We've done it on all our rally cars. The "theory," is as stated-keep the TB as cool as possible to avoid warming the air charge any more than it already is.

Does it work? I know that many reputable Subaru rally car builders do this. We obvious run the rally car in the winter and have had no trouble.

Don't forget that your ICS(Idle control solenoid) is right near the coolant passageway. I'll leave it to a Subaru mechanic to tell us if the ICS is affected by the lack(or presence) of coolant.

There would be no performance reason to do this on a street car that I can see.

FWIW, we also don't water cool our turbo on the rally car.

Regards, John