Doing a 305-350 swap and have to install a sensor that is not used in the new block. It is on the pass. side very near the top. There are 2 sensors I can see on that side, one near the bottom (knock sensor?) and the other one I mentioned. I think it goes into a water jacket. If it is some kind of temp sensor then that makes 3 water sensor used on the block, why would they need so many?
Thanks,
Bob

 

If it is above the starter solenoid between plugs #6 & #8, it is the heavy duty coolant fan switch and has a single wire connector to it.

 

Sounds like that is it. Heavy duty? That's interesting, I have a single fan setup (92 RS), does that sound right?
Thanks
Bob

 

That switch is for the dual fan set-up if you decide to go with it. Heavy duty is what it is referred as in the manuals and parts department. It is also known as the secondary fan switch. Also, if I remember correctly the 305 TBI only had a single fan set-up.

 

Hmm, so if I only have a single fan setup (from the factory) then is this the sensor that turns on the fan anyway or something else?
Bob

 

the ECM does not turn on the fan in the single fan setup.

that switch goes to ground when it gets hot enough.
that grounds the fan relay.





in the TPI dual fan setup that Trickster is reffering to, that switch only turns on the 2ndary fan if the primary, ECM controlled, fan isnt keeping it cool enough.

 

btw, yes there are 3 coolent temp sensors.

passenger side head is fan turn on
intake manifold is for the ECM
drivers side head is for the temp gauge / idiot light.


be sure to get the correct sensor when replacing... most auto parts stores just have all 3 under coolent temp sensors.

 

Is this the sensor in question? If so, it is the coolant fan switch.

 

Yep, all 305 TBI came stock with a single fan. You are correct, the sensor near the bottom that you mentioned is the knock sensor, and the sensor located in between the #6 and #8 spark plugs is the fan switch (it's what turns the fan on, FYI), just like Trickster said.

Our cars have 3 sensors because we need them, lol. If I remember correctly, the sensor on the driver's side cylinder head in between the #1 and #3 spark plugs is the coolant temp sending unit (what the gauge uses to show coolant temp), the sensor on the intake manifold is the CTS, coolant temperature sensor (what the computer uses to read coolant temp), and the sensor on the passenger side cylinder head in between the #6 and #8 spark plugs is the fan switch (what the fan uses to read temp and turn the fan on or off).


EDIT: MrDude_1 beat me to it. Oh well.

 

Shifty, yes that is the one.
Guys, thanks very much for the quick replies, you have really helped me out with this one.
One last thing, the auto stores would'nt happen to have different temp range sensors so I can get the fan to come on earlier would they? Otherwise I will get an external fan controller to do the same thing.
Thanks again
Bob

 

Most parts store won't but you can buy one from jegs. I think it is a 160* or 180* unit. I am not sure. It is listed in their catalog though. I think it is like 20 bucks or so.

 

yes you can get them for diffrent temps.
however, i cant remember any cross refs off hand.

a search on here should give you some part numbers... i blieve theres even a NAPA one thats adjustible.

 

Yep, you can get different temp ranges for the fan switch. That's what I did. I bought the Hypertech one for $40, it broke on me, so I went and bought a $10 and I couldn't be happier.

I'll find the part numbers for you. Just give me a second.