I have a 92 RS W/305 with no modifications.... I've been having a cooling fan sensor problem since I purchased the car a year or so ago. I've replace the sensor no less the five times over the past year. It/they work for a while and simply stop. I've tried NAPA, Autozone and O'Reilly with the same results, works for a while then nothing! Changed the relay thinking it may be the problem but that wasn't it, same issue, works for a while then nothing. AC system works great, turn the AC on and the fan comes on. Turn it off and the fan goes off. So I know the electrical ckt is OK, at least on the AC side. I decided to installed a manual switch in the car so I could turn the fan on manually. It came in handy a couple of times but I would like the system to work they way it was intended, automatically.

Any ideas or input on what the problem could be would be very much appreciated...

Thanks,
Ron

 

the wire that goes to the switch or temp switch is a ground. when the engine gets to the desired temp the switch closes and completes the circuit. the replacement that your buying from the part stores are cheap if you dont buy Delco or name brand stuff. i worked for pepboys and advance auto parts for a while for part time work and to get a discount on my parts i needed for my car. anyway they sell cheap **** if its not name brand stuff. that why it keeps failing. just to make sure theres nothing wrong ohm out the wire or ground it and the fans should come on. if they dont you got an issue up stream on that wire.
i hope this helps a little. also the green wire on the relay for the fans is that wire that goes to that switch. try an A/C delco part and you should have a better result, the stuff they sell in part stores are cheap china junk. thats why there cheap. also beware of dealers i worked in the back in the commercial counter and you would not believe how many company's buy there parts from parts stores and charge dealer prices for the same stuff you can buy. a certain tire store paid 20 bucks per rotors but charge the customer 100 its crazy.
i delivered 4 rotors and 4 calipers,and pads they(tire store) paid 200 for all of it and charged the customer 1200+ and thats after giving them a deal as he said. i have no problem with making money but thats a insane
any who hope this helps alittle

 

couchmotors,

Thanks very much for the information.

You are of course correct re. the cheep crap they sell at the parts stores. I am actually getting good at changing the switch. It's just a real pain the the butt to continue chasing my tail and not getting any closer. Delco products are hard to find here so perhaps I'll take your advice and order one on-line.

Thanks again for the information.

Ron

 

or your local GM Dealer

 

I realize that there can be a significant difference in quality when looking at aftermarket parts but I have to be honest, I'm skeptical thats the cause. I have a few suggestions for you.

First, how do you know the sensor is actually bad? Have you measured it? Just saying you may just have a bad connection and it gets disrupted after changing the sensor.

Second, can you measure the current going through the temp which when the fan is running?

 

Check the fan relay and the wires going to the relay. My car for the longest time kept burning up relays. It turns out, it was the wiring going to the relay. It has become loose with age and needed to be reseated. Just pushing up in there real good. In the end, I threw away 4 good relays.

 

mantaguy, thanks for the information. I'll give them a try for information and perhaps a DELCO replacement. Interesting, I looked at the DELCO site and they offer three coolant fan sensors? Not at all sure what the difference is will have to research it further. It's never easy!!!!

rolling thunder - yes I measured the sensor after failing and it was an open ckt. There was no safe way to test the component as the on or close temp was over 220 degrees. However, when I replaced it the system once again worked as it should. QED, bad coolant fan switch. Also, no I have not measured the current that is something I need to do. I think you may be on the right track and I really need to know exactly how much current is being drawn as that be significant.

Ozz1967 - In these older cars there is always the potential for bad or cooked wiring. I have looked ate it but have found no significant indications to tell me there is a problem. Does not mean there isn't just have not located it if there is one...

Thanks everyone for your input and suggestions...

Ron

 

Easiest way to test the switch is to place it in a pot of boiling water. Connect up a multimeter to it and measure the resistance. One lead to the terminal, the other lead to the threads on the switch. You won't "see" the switch close completely (0 ohms), but you should see it get real close. Or you could get the engine up to temp, and connect one lead from the multimeter to the switch terminal and the other to the braided engine ground strap. You should get 0 ohms if it is grounding properly through the head.

Also, are you using a switch with 1 wire connection or 2? A switch with 1 wire grounds through the threads into the cylinder head. If you used too much sealant or pipe tape on the threads, it will not provide a good enough path to ground for the relay to close. Or you could have gunk from the coolant seeping into the threads and preventing a good ground. I'd suggest getting a good switch(Painless Performance/BeCool, etc) from Summit or the like that has 2 wire connections. One goes to your relay wire and the other to a good ground. I installed the 2 wire Painless switch when I swapped to a V8 and have never had a problem with it turning on.

 

RS2... Have tried the boiling water but never had much of success. I'm currently using the single wire switch. Stock.... I've considered the possibility of too much resistance as you suggest. Have not taken any accurate measurements yet but it is something I intend to do. Can you tell me the manufacturer and part number for the two wire sensor you are using. I'd like to look into that as an alternative approach and perhaps the solution.

Thanks,
Ron

 

I have this one:

http://www.summitracing.com/search?S...word=prf-30111

It turns on at 185 instead of the stock 220, so your ECM may not like it much. But I know they make one that turns on at 195 which should be close enough to prevent any issue with the ECM. I never looked for one that turns on at the stock 220, so I'm not entirely sure they make one.

 

They sell switches for every temperature from 160* on to 238*on and everything in between. Jegs or Summit will carry them. I use a 195* on fan switch for my primary and *212 on for my secondary fan.

 

I would stray away from Hypertech if you're looking for a new fan switch.

 

I used hypercrap switches for years without issues, other than breaking one during a header install.
Having said that, I just tried to buy one 2 weeks ago and they are discontinued so I ordered a different name brand, one from Jegs and found their supplier has them 5 bux cheaper. Buuuut it was only like 9bux from jegs.

 

Well hear me out here. Something doesn't quite make scene here. I think either the sensor is actually not failing as thought or there is something wrong in the circuit causing it to fail.

Because I think it's most likely a connection issue, it is important we verify the senor is bad. If you measure the sensor while its cool, it will measure open. If need be, build a jumper wire so you can test it on the car while its hot. I think the connector itself is a likely candidate but it could even be something more exotic like corrosion between the block and the sensor (current (to turn on the relay) flowing through dissimilar materials (block vs sensor) in the presents of an electrolyte (antifreeze) rapidly accelerate corrosion).

Second if not a connection issue, what about current? What if a previous owner got the bright idea to ground the fan through the temp sensor because they couldn't fix the real issue? Something like that would burn that sensor up in fairly short order.

Just some things to think about.

 

You made out better than I did. Mine turned on WAY early and would never shut off. I did some searching here and quite a few people had the same problem. I purchased another switch at Autozone which was much cheaper and it worked great.