View Full Version : Strange effect after IC fan install...

07-01-2002, 09:17 AM
So I added the 8" Permacool fan to my intercooler using a preset 170* thermostat switch with power coming from the ignition wire (just outside the fuse box). It works as it should but now I notice the following:

After the engine has been running for awhile and I shut it down, there is a slight delay before the engine stops after the key is in the off position. You can hear that air sucking noise and that valve behind the sc closing.

It doesn't seem to be a problem, but it has never done this before and I'm having trouble seeing how it is related to the IC fan install.

Any ideas on this?


07-01-2002, 09:31 AM
hmmm. i dont know about the delay, but i ALWAYS get a sucking sound and the valve closing.

07-01-2002, 09:39 AM
Hmmm... Maybe it has something to do with the seal on the IC tubes, where they meet the IC? After removing the IC, I used the gaskets made by Tbird88 on the re-install. Perhaps they were not sealed properly before, and now they are - would that make a difference?

07-01-2002, 09:42 AM
Have a buddy shut the car off while you listen under the hood. It's really hard to track that down when your head is in the car.

The one time I heard that type of sound on shutdown it was the big nut on the SC outliet pipe cam loose. The sound was echoing and sounded like it was coming from the firewall. I couldn't pin point it until I had someone help me.

07-01-2002, 10:00 AM
I actually had the hood up and was looking into the engine when my girlfriend turned the car off. Behind the sc there is some kind of round valve control that is attached to the plenum, I believe? This is where the noise is originating from, and I can see the valve snapping shut.

07-01-2002, 10:32 AM
That is 100% normal. That valve is what controls the amount of boost that goes into the engine and is vaccum operated. The noise is just vaccum escaping while the valve opens up and comes to rest.

07-01-2002, 10:38 AM
Cool. So what would be the reason my SC never, ever did it before? Vacumn leak at the tubes?

07-01-2002, 10:42 AM
That is the bypass valve and is used to route recirculated air through the SC when boost is not called for.

I guess I took a hard look at it when I had my problem and could really see no reason for it to leak. It wasn't until I put my ear right down next to it and duplicated the problem that I noticed the nut on the top was loose. (I grabbed it for leverage and it moved)

I would really check that nut.

07-01-2002, 12:05 PM
the fan is acting as a generator make 12 volt power wire it from bat so it dont power acsessorys and ignition.. when its winding down

07-01-2002, 12:14 PM
Interesting! I had originally wired it to the battery, but did not like the fan staying on while the car was shut off - at least until the engine coled to below 170*... Would a 1 amp diode prevent the situation you described - like you would use in a cool fan switch for the high speed fan? If nothing is done, is there any harm in the effect that is being caused??

07-01-2002, 12:25 PM
I don't think a 1 amp diode would be enough, the fan probably draws more than that.

Use a relay to power the fan from the battery and activate the relay using ACC power. The 1 amp diode would be useful to reduce inductive kickback from the fan, just make sure to connect it across the fan such that the marked band is to the positive side (battery). If you get it wrong you'll have to pick up the pieces of the diode but that's about all.:eek:


Edited for stupid typing mistakes - too much coffee

07-01-2002, 12:34 PM
Cool, sounds like a plan. Do you know where to splice into ACC power? One of the wires (wire color?) in/out of the fuse box by the battery?

07-01-2002, 12:43 PM
i bought that same fan though Jegs and i wired it up to my rad. fan and cut the 14 wire off the wireing harness so when the key turns on so does both fans....

i really didnt want to mess with the other wire stuff like you but i give hand claps.lol

07-01-2002, 01:07 PM
Originally posted by joenintiesc
Cool, sounds like a plan. Do you know where to splice into ACC power? One of the wires (wire color?) in/out of the fuse box by the battery?

ACC = accessory power