NW94Z

Does using teflon tape on the threads of the coolant fan switch to seal it to the block interfere with it's function? I recently replaced mine coolant fan switch and the fan still isn't kicking on. I can ground the wire to the coolant fan switch and the fan works but when I plug it into the new switch it does not. Bad switch? Is the tape interfering with the sensor grounding to the block? Does the sensor ground to the block?

thepoz89

the switch grounds at the block. There is only one wire going to it right? The block is the ground then.

NW94Z

Yup one wire (green). So if it does in fact ground to the block then the teflon tape would prevent that from happening?

Sonix

iTrader: (1)

Teflon tape is needed to keep it from LEAKING. It's pipe thread, that stuff is a necessary evil. Check the continuity with an ohm meter between the block and the body of the switch, I can almost guarantee it'll have perfect continuity, in spite of the paper thin spec of teflon tape.
It's not turning on because your engine isn't getting hot enough. What fan switch temp are you using? Stock turns on at like 214* F.

naf

iTrader: (7)

Agree with Sonix, unless you put gobs of the tape on there you're probably fine. A continuity check wouldn't hurt though. In the future try some teflon sealant I find it much easier to work with than the tape.

NW94Z

The new switch is the same as the stocker. I think it kicks on at like 229 and off at 213. The engine is definitely getting hot enough, based on the gauge in the dash and the bubbles I can hear when I shut the engine off as soon as the needle passes the last white mark on the gauge.

I rounded the threads twice so to layers of tape. I'll just remove the sensor and take the tape off. Then either use the sealant you describe or put less tape on fewer of the threads.

Sonix

iTrader: (1)

No, the tape isn't the problem. Perhaps a faulty switch.
Check continuity between the block and the shell. If your multi meter beeps, then it has nothing to do with the teflon.

Did you bleed the cooling system of air?

//<86TA>\\

iTrader: (14)

tape will not effect the sensor, it only ends up filling tiny imperfections in the threads and the rest gets chewed up on the way in.

with the car on, grab a little piece of wire, stick it in the pigtail and ground it out to the block. The fan will turn right on. If it does the sensor is problematic, if it does not turn on there is another problem

naf

iTrader: (7)

And don't use the dash temp guage as any source of accurate information on the actual temperature of the coolant at the fan switch. These guages are terribly inaccurate.

NW94Z

No didn't bleed the cooling system of air. Is there a bleeder valve like on the 4th gens?

I've verified the the wire/ connector are good by grounding to the block. That's why i still think the sensor is bad or there is to much interference from the tape.

I agree the dash gauge is very inaccurate but when I shut down and can hear the coolant bubbling and the fan never came on then I'm pretty sure the car is getting hot enough.

naf

iTrader: (7)

If the cooling system is not under pressure the water/coolant will boil at a much lower temp than the setpoint for the fan switch. A leak or bad rad cap can cause this.

I always drill a small hole in the side of the t-stat to keep air from getting trapped in the block.

Sonix

iTrader: (1)

Bubbling makes me think there is still air in the system. It'll be hard to get the system pressurized and hot enough to open the thermostat (and then turn on the fan).

No bleeder valve (we're talking about your '91 RS 305 right?), you just need to add coolant to the highest point. Make sure the block is completely full. You can remove the thermostat and add there, or add in the heater core hose. It's not a crucial thing, you gotta be pretty far off to screw it up. If the car is cold, i'd pop off the t-stat housing and see in there. If you don't see it chock full of green wonderfulness, then top it up there.

It's not the tape, but you might have a bad switch. That's hard to test. Top it up and run the car until the fan turns on. Don't shut it off until the rad cap blows off, or the switch turns on.

naf

iTrader: (7)

The switch can be tested by removing it and heating it with a continuity test between the input terminal and the switch body. The difficult part is determining at what specific temp it's at when it turns on/off. With lower setpoint switches you can submerge them in water on the stove with a thermometer. Hard to get boiling water much above 212 degrees F., on the stove anyway.

That's like 100 'Centi' degrees for those not familiar with the accepted standard.

NW94Z

Thanks for the continued advice guys.

First off yes this the still the 91 RS I'm talking about. My 4th gen has 28k on the clock and is still as good as new.

Here's what I'm going to do. After reading through this link (https://www.thirdgen.org/cool) I'm going to install a 170 stat after drilling four holes into the body as described. I'll be topping of the coolant at this point if it needs it. Install a new coolant fan switch into the block and see if this fixes the problems. If not then I'm then going to install the Hayden switch that attaches to the radiator per the link above and call it all good. I'll try to get this done this weekend or some time next week at the latest.