Guys this is weird. Here is a pic of my fan switch from my 86 305 tpi. I tried to find a replacement part, and the threads on all the replacement parts are 9/16"--this is on ALL the replacement parts I could find, from three different parts stores. I don't understand. The threads on the original part in the picture are 3/8". I ended up having to get an npt adapter and screw it into the block and then screw the fan switch into the adapter (of course, my fan still doesn't kick in correctly ). Anyway, as far as the thread size being wrong, does anyone know what's up with this? I even checked on first, second, and fourth gen sbc's, and still there were no parts to match the threads as the part in the picture. I am baffled by this.

That's a knock sensor, not a fan switch. It goes in the block water jacket drain hole on the passenger side, near the starter.

The fan switch goes in the passenger side head.

The connectors are similar.

Holy CRAP you're kidding me. So, the knock sensor has the single blue wire and it attaches to the block right in a coolant passage? WTF? Where the heck is the fan switch then? I couldn't find the darn thing?

I think thats your knock sensor not your fan switch.Because on my 91z the thread size is 3/8.

Ithink on yours it is in between third and 4th spark plugs. Mine is right above starter .

Wow, twenty years of wrenching, and I made that kind of a mistake. It happens to the best of us, I guess. I guess I better put it back on my car then. Might as well get a new one to put in there. I searched and searched for the fan switch but could not find it on the engine-stupid air injection crap won't let my arms and hands fit in there. I guess I'll have to search harder.

The fan switch is actually between number 6 and 8 spark plugs. It will be underneath the little heat shield piece for the AIR tubes. Should have a single wire lead to it that runs in the conduit top of valve cover, under alt and towards starter.

I have, however, heard rumors that some early TPIs did not use the fan switch but relied on the ECM to control the fan. Very few rumors, mind you.

This is the fan switch, right here in the cyl head next to the dipstick. I replaced it with a later weatherpack style unit but it's in this location

If you want to believe this Autozones website says its on drivers side below the exhaust manifold in the block for fi cars

Thas the knock sensor for sure.
The fan sensor as said are above the starter near the head/sparkplugs.

Buy a new knock sensor and put that in, never use old sensors like that again after removal, It have done its job and you will get a better monitoring with a new sensor.

tpiparts have them at a good price to. or rockauto

If its an 86, I think there was only one option... the single fan. If you have a single fan setup, you do not have a fan switch. Its ECM controlled only, from a coolant temperature reading through the coolant temp sensor. The fan itself is powered through a relay and triggered by the ECM.

According to my Autozone search, this is your fan switch:

http://www.autozone.com/autozone/cat...ndName=Santech

{don't use think link for ordering, this is for my local store, not yours!}
Which looks just like all the others I've seen. It does say Radiator in the description, although it goes in the pass head between #6 and #8 plugs as described above.

I see where Autozone reports the location on the driver side - I think it's human error in the typing of the description or the programming of which description to use in the website.

Actually, there are two switches/sensors or whatever you want to call them, on my intake manifold right in front just below the TB and on the left--I was told that one of them sends a signal to the ecm about the engine temp, and the other is the fan switch. The fan switch is on the left, and the signal sender is on the right. Weird. I'll take some pics when I change out my water pump, and I'll post them here.

Neither of those is a fan switch. One is the coolant temperature sensor that reports temp to the ecm, the other is a thermo time switch for the cold start injector. If you have a single fan on your car, you do not have a fan switch.

Ahh, I see. So, maybe the sensor that sends the temp to the ecm is bad. I got a new one coming, so we'll see.

QUESTION: What happens when the knock sensor wire is plugged into a fan switch, and the fan switch gets hot and grounds out the knock sensor wire-does it then retard timing and make the engine run like crap?

Also, you can have a new "fan on" temperature put into your custom chip, right?

The reason I ask is because stupid me thought the knock sensor was the fan switch, and the knock sensor wire is still plugged into the new fan switch at the knock sensor location, and my car feels slower than before.

Now Iam confused if it does not have a fan switch why do they make one? Did you put the same wire back on that you took off ? Did you take the adapter you made off and put a new knock sensor back where it belongs?

That particular application does not use one. If there is one listed in a parts search, the search is wrong. That is more common than anything, I used to sell parts and parts listings always have errors.

This may be year dependant, but is NOT ALWAYS THE CASE. The later model RS cars have a single fan, BUT they do definitely have a fan switch. My 1990 and 1992 both had fan switches.

I think you are right about being year specificmines a 91z28 but it is a 350 with dual fans. I know I dont agree with autozones location. The guy with the picture seems correct but he has his engine listed as a 87 350. WELL WE ALL AGREE HE TOK HIS KNOCK SENSOR OUT.

I haven't taken off the adapter and switch yet. I just unplugged the knock sensor wire. I haven't had the time to mess with it.

Ha ha...I sure did. I was tired that day.....REALLY tired.