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Installing An Aftermarket Radiator Fan Temperature Control

5710 Views 3 Replies 3 Participants Last post by  David Eidell
1995 Dodge Spirit 3.0 V-6

After long and painstaking troubleshooting I zeroed in on why the radiator fan refused to come on unless the A/C was switched on. I replaced all the sensors and the pigtails and soldered them. The relay is working fine but apparently the signal just isn't doing anything between the relay and the computer or in the computer itself. A couple of aftermarket AutoZone kits with the probe that jams into the radiator fins have come and gone and I'm tired of running the fan through a bosch relay connected to an ignition signal.

I purchased a cast iron thermostat housing that has the identical dimensions of the OEM. A machine shop drilled and tapped a hole on top for a standard contact (two .250" male faston connectors). I purchased the temp sensor which is marked 190 degrees. My plan is to change to the new system, run a new harness to a new Tyco relay protected with a 25 amp ATO fuse, I will use the existing ignition signal wire to trigger the relay. I will not involve the nearby computer thermal sensor in this modification.

I will refill the radiator until water bleeds out of the top of the new cast iron thermostat housing then tighten down the sender and connect the wires.

But before I start, I certainly will ask for opinions. I am 74 miles down a dirt road off Mex 1, 550 miles south of the US border, and I tend to be a bit more conservative before disabling my auto. I have new metric fasteners to replace the OEM when doing the job. Thank You in advance.
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Wrong side of radiator. You want the fan sensor on the ouput of the radiator, not on the output of the engine. With the thermostat housing location the fan will run all the time.

· Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
17,321 Posts
I would lean towards wanting to find and fix the problem first, maybe even if it was up to a failed PCM.
Be sure that you are looking at the right CTS (coolant temperature sensor) as there are two of them. The violet wire one is for the dash cluster gauge. The 2-wire one is the temp signal for the PCM and is the one you want to test and/or repair. I believe that the supplied 5v return voltage should drop as the temperature rises. Checking this return (signal) voltage at the PCM connector would also test the integrity of the entire supply/return circuit of the CTS. Do you have a service manual wiring diagram for the car?
An OBD I scan tool with the Chrysler connector would show what the PCM sees in the way of temperature readings and also radiator fan relay on/off state.
Is there a radiator fan relay or CTS fault code?

· Registered
387 Posts
Discussion Starter · #4 ·
Thanks ImperialCrown!
Yes the voltage is present, and if anything is disturbed meaning disconnected, the check engine light comes on, the car loses converter lockup and overdrive + runs crappy. I tried four new different sensors including OEM and two pigtails, both soldered to the OEM harness. There are no fault codes. I do not have access to OEM wiring diagrams nor troubleshooting bulletins. I am sort of stumped and must keep in mind that I am a long hard four day drive from the US border. At the time I was in the USA and tried sensors and pigtails I foolishly believed that the aftermarket fan control would do the trick.

I guess what I should be asking is if the disconnecting of the sensor lead with results as noted above is a positive sign that the problem lies in the ECM? The relay near the DS strut tower has 12 volt power to it, the load side energizes the fan when pigtailed to a 12 volt source and a replacement new Tyco relay does not change any of the symptoms. One side of the relay coil energizes with ignition. A Chrysler tech told me over a Skype connection (fee service) that he "never has heard of a computer fan control circuit failing in the computer". Either whatever signal leaves the sensor on the water jacket splits up before entering the computer or I am left with one dead part of the computer.

I purchased the car used with extremely low mileage. It was purchased in the month of June in warm country. I did not switch the air conditioning off until November. What a surprise I got. With 70,000 miles on the car at the moment, I'd hate to write the engine off by me being stupid around an alumunum engine and overheating.
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