ok i have a 91 hatch i just put a b16 in it, and now im going over all my wiring, and the coolant temp sensor right below the VTEC valve is plugged in, BUT it looks like theres another sensor on the thermostat housing. but i have no plug for it. does anyone know what this sensor does? and could it cause my high idle?

my car started after a few good cranks. and it idles at like 3000rpm and goes up and down, so i searched that, and im gonna clean out my IACV and screw in the FITV. but other than that could this little sensor on the t-stat housing be a problem?

 

That plug on the thermostat housing is for your fan switch. On obd0 cars it was a two-prong fitting found on the back of the block by the oil pressure sensor. You have to cut the plug, extend it and add the right plug to fit your motor. I'm assuming its a second or third gen b16

 

my car is OBD1 now. so i have all OBD1 harnesses. only thing that is factory 91 civic is the interior harness

 

and if thats my fan switch, how come my fan turns on when the motor is running?

 

Is the fan on %100 percent of the time or does it kick on and off?

 

its on all the time , maybe the owner before me hardwired it. idno.

 

mine is like that too.

well on the temp housing it looked like something was supposed to screw into this big hole on the side but i just placed a plug in there.
i think the owner before me hardwired it so that when i turn the ignition on, the fan turns on too. it doesn't bother me though.

 

well the problem is, i just got done with my motor swap and im trying to fill the antifreeze. and im running a FAL fan and a Fluidyne half sized radiator. and with that combo and the fan running all the time. my thermostat will never open! lol. looks like i need to leave the fan unplugged for a few minutes to fill the system

 

hahaha yeah thats true, or you might need to put a switch on the fan.

 

Yah prob put a switch or just buy a fan switch to go in the hole. So you're actually running obd1 harnesses? I remember on my zc hatch I had a stock half rad and no fan. On the freeway the temp would go down to the c. There's really no need for your fan to be on all the time. Your car must be at normal operating temps for vtec to efngage