BergRacing21

so i've done quite a bit of searching but i wanna see if anyone else has had a similar problem as me.

So i just recently put in my swapped motor that's ready for boost. But i'm having a overheating issue. I switched my full size radiator with a Mishimoto triple core....and replaced ALL sensors. I have no issues when driving the car but if i let the car sit and idle it will start to overheat...i've never seen how far i only let it go above the normal op before i shut it off. But the fan won't cut on AT ALL when running. the minute i turn the key off the fan will cut on. Which i know is normal. My question is whats causing my fan to NOT cut on while driving. I'm trying to put 500 miles on it just make sure rings and everything sit fine before throwing my turbo on it, but this might be a problem in the area i live in cause of stop and go traffic.

So from what i've read i may still have an air bubble in the coolant tube? wouldn't popping the bleeder at the thermo when hot get that out? other scenario is just the fan relay is bad....but why would it cut on after the key as turned off. and last i read was the actualy fan module the black box located by the ECU...but will that go bad just to cause the fan not cut on while running? I'm 99.9% she's been aired out fine but i could be wrong maybe i have a bubble trapped somewhere any guesses?

**also note all my coolant lines are recirculated taking the heater core out the situation since its a race car, will that make a difference?

motoxxxman

bypassing the heater core will not make a difference, no.

might be a bad body control module, I don't know where that's located though.

are you sure you used the correct coolant switch in the radiator? the one in the radiator is a switch, off when cold, on when hotter than a certain temp. start the car, and with it idling unplug the coolant switch in the radiator and jump the two terminals in the harness plug for it, the fan should come on. if it doesn't, then you have bad wiring somewhere, or a bad body control module. if the fan does come on, then that switch is probably bad.

and btw, the bleeder screw is only for bleeding air out with the engine OFF, when assembling a rebuilt motor and putting coolant in it for the first time. 90% of people have the wrong info on what the bleeder screw is for and how to use it.
to use it you: 1) loosen the bleeder. 2) fill radiator. wait. 3) slowly keep filling the radiator as the level drops. 4) continue filling the radiator until pure coolant and no air seeps out the bleeder. 5) close the bleeder. 6) top off the radiator and put the cap back on. 7) start car and let it warm up.
once you fill the coolant initially, you never need to touch the bleeder again. the cooling system is self bleeding every time the thermostat opens. all air will trap in the radiator, so to get rid of air, just fill the radiator when cold after it's been driven a few times.

oh, and no an air bubble in the cooling system will not cause the fans to not work. the switch for the fans is in the bottom of the radiator, nowhere near where any air could get trapped.

and lastly, when you say the coolant hoses (heater core hoses) are recirculated, I really hope you mean you connected them together. because if you just capped or plugged those lines on the engine side, yes that will cause overheating.

holmesnmanny

warm the car up and as soon as it starts to look like it's overheating turn it off and check for continuity at the fan switch at the thermostat housing...should be continuity...if there is then the issue is downstream maybe the relay

did you buy a Honda fan switch ?

BergRacing21

Got ya, i'll try a few of those things. I never did touch the bleeder it was just something i read on another topic/thread lol. Yeah the hoses are connected together.

okay, i'll give that shot. This is mainly what i was reading about so i probably shouldn't even started the thread but i definitely appreciate your feedback. but no i didn't buy a OEM switch i think i got a beck/arnley or some other pretty well aftermarket name off rockauto.

holmesnmanny

you could try swapping another relay with your fan relay to test if it's your relay if you don't know how to test it

spoolinlude

You have a fan circuit problem. Air in the system and the rest of the stuff you mentioned isn't the problem. If you're reading high on the temp guage and the fan isn't turning on you have a problem. Make sure you have all the wiring correct. I think the power steering temp (Still don't get why they have one) and the fan switch on the head are the same plug.

Never buy aftermarket sensors/electronics for Honda's.... they never work right. Almost like Honda made their stuff to only work with their replacements.

motoxxxman

just to point out there's a bit of confusion here among some of us including myself:
different years had different setups. the main thing you're looking for is the fan coolant switch; some years it was located in the bottom of the radiator, some it was located in the water outlet.

careful with what you do to test the different sensors on the water outlet though, as that is also where the coolant temp sensors are located, which are different than a fan coolant switch.

BergRacing21

Yeah, i think i'm just gonna have to trace stuff. The thing that really throws me off is that it will cut on when the cars OFF. But that's exactly what's happening is if i'm sitting at idle and let it warm up it will begin to overheat and no fan. There was a sensor in the PS hose. I removed my PS and converted it to a semi-manual rack by looping the lines with a breather. But from what i was told that sensor didn't matter. I'll just start testing the stuff and/or buy an OE switch. I do have a 94 prelude too...so i might try that fan module or whatever cause my other cars fan works lol...i looked it up a few days ago i forgot the proper name of it see if maybe that works for this car.

@motoxxxman sorry man, i didn't specify but it's a 92. and i guess the term i was looking for early was 'loop' the coolant lines are looped cutting out the core.

nemesis25

I had a similar issue, it turns out my ground for the thermo switch was broken. All I did was I
Ran a new ground from the chassis to the Valve cover.

Acidcrakker

The fan control box is small maybe 4x2 up and to the left of the ecu.

Your issue is going to come from there.

BergRacing21

thanks for all your help guys. you're exactly right Acid it was the box i swapped it from my other lude...it works now. After tracking all these wires and relays it was just Two diodes and a capacitor were burnt out in that module...i got some HQ pics i'ma upload in a bit to show it, i just wanted to let everyone know i figured it out.

BergRacing21

Bulging capacitors


Two broken diodes

Acidcrakker

Takes alot to figure exactly what the issue is.

motoxxxman

oy, I wonder what caused that. very glad you figured it out though, and everyone loves pics