Function of sensor in radiator, 1988 2.8 MPI

1988 2.8 Cavalier Z24 has overheating issues. Coolant fan doesn't kick on at high temp, but will run strong when a jumper wire is connected from batt
ery positive. Someome put another relay on it but problem persisted, unplu gged the new relay and saw that old, gummy dielectric grease from the harne ss receptacle got all over the prongs of the new relay. Blasted both clean with electronics cleaner as best as I could, but still no fan at high temp . I notice the car has a single-wire sensor plugged into the front of the radiator, and I'm guessing that is what sends the signal to the ECM to star t the cooling fan -- correct? It also uses the two-wire CTS mounted on the engine, which I presume feeds to the ECM to interface with the other senso r readings for optimal emissions and power, etc. Is the single-wire sensor likely the culprit? Also, what is the best way to clean out a multi-prong plug receptacle (like the fan relay here) to get rid of all that old diele ctric grease -- seems VERY hard to get it clean.
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ednaboopadoop wrote:

best i recall:
single wire sensor is for gage (or idiot-light).
Two wire sensor is for ECM. ECM controls fan relay.
You need a scan tool that can stream data on that ancient beast to see if the ECM is "seeing" the proper temp from the sensor.
I would use brake cleaner and compressed air to un-goop a relay socket.
GW
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On 9/9/2013 3:05 AM, ednaboopadoop wrote:

Suggestion: stop guessing and get the service manual so you know what you are working with.
--
I'm never going to grow up.

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On Thursday, September 12, 2013 6:37:12 AM UTC-5, PeterD wrote:

I couldn't find one, which is why I posted -- but I since did find one on eBay and it should be here today. BTW -- wouldn't your reply apply to pretty much absolutely any post on here? ("Get a service manual and figure it out yourself")

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On Monday, September 9, 2013 2:05:48 AM UTC-5, ednaboopadoop wrote:

ttery positive. Someome put another relay on it but problem persisted, unp lugged the new relay and saw that old, gummy dielectric grease from the har ness receptacle got all over the prongs of the new relay. Blasted both cle an with electronics cleaner as best as I could, but still no fan at high te mp. I notice the car has a single-wire sensor plugged into the front of th e radiator, and I'm guessing that is what sends the signal to the ECM to st art the cooling fan -- correct? It also uses the two-wire CTS mounted on t he engine, which I presume feeds to the ECM to interface with the other sen sor readings for optimal emissions and power, etc. Is the single-wire sens or likely the culprit? Also, what is the best way to clean out a multi-pro ng plug receptacle (like the fan relay here) to get rid of all that old die lectric grease -- seems VERY hard to get it clean.
The single-wire sensor in the radiator runs the low-cooland idiot light. T he problem with the fan turned out to be the fusible link, which hooks up t o the battery junction block on the firewall directly behind the master cyl inder. Replaced fusible link with an in-line fuse holder.
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On Thu, 19 Sep 2013 10:48:31 -0700 (PDT), ednaboopadoop

Thanks for posting the solution. I wish more people would.
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On Thursday, September 19, 2013 12:48:31 PM UTC-5, ednaboopadoop wrote:

battery positive. Someome put another relay on it but problem persisted, u nplugged the new relay and saw that old, gummy dielectric grease from the h arness receptacle got all over the prongs of the new relay. Blasted both c lean with electronics cleaner as best as I could, but still no fan at high temp. I notice the car has a single-wire sensor plugged into the front of the radiator, and I'm guessing that is what sends the signal to the ECM to start the cooling fan -- correct? It also uses the two-wire CTS mounted on the engine, which I presume feeds to the ECM to interface with the other s ensor readings for optimal emissions and power, etc. Is the single-wire se nsor likely the culprit? Also, what is the best way to clean out a multi-p rong plug receptacle (like the fan relay here) to get rid of all that old d ielectric grease -- seems VERY hard to get it clean.

to the battery junction block on the firewall directly behind the master c ylinder. Replaced fusible link with an in-line fuse holder.
The 20-amp fuse in the new fuse holder popped immediately when the fan wa s energized. The fusible link said "20" on it, so I presume that meant 20 amps was the max that circuit could draw. Will a powerful motor like a rad iator fan pop a 20 amp fuse during start-up, where a 20 amp fusible link wo uld not melt during the same period? I chose the fuse-holder to avoid the hassle of cha nging the fusible link in the event of future overload.
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ednaboopadoop wrote:

From what you have said, the fan motor is bad. It should never pull that much current, and a new one won't.
GW
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On Mon, 23 Sep 2013 18:29:43 -0700 (PDT), ednaboopadoop

Fuses are intended to blow FAST. Fusible links are intended to be much more forgiving of short term overloads. Like the other poster said, it could very well be the fan motor is bad. I'd get another fusible link and see how long it lasts. You can get them at any auto parts store.
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