- Location
- Antioch, CA
Recently, I had the the chance to upgrade a friends 87 XJ from the old style closed radiator to the newer open style. When researching this conversion, I found lots of how to web sites for the basic replacement of the radiator and heater hoses, but it became somewhat muddled when it was time to wire up the electric fan. The big problem was how to control the electric fan operation without using the factory switch. Most sites just directed you to your local parts store for some aftermarket thermostatic fan control assembly and wire it in. Some even directed you to buy the 91 and up coolant temp sensor for the computer and hook it up in place of the original fan switch. I doubt that would ever turn on the fan, or the sensor might short out and the fan may even run constantly. There had to be a better way.
Well, after doing some digging in the GM parts catalog, I came across a coolant fan control switch for an Oldsmobile FWD car. The switch is calibrated so that when the temp reaches 105*C (somewhere close to 220*F?) its internal switch closes. Now this switch only has one wire attached to it. We used this switch to ground a relay that we installed in place of the original radiator mounted fan switch. This GM switch will screw directly into a 91+ XJ 4.0l thermostat housing(the 87-90 XJs do not have a port for this sensor in their thermostat housing). For the relay, we just cut the wires going to the original switch, then we attached these 2 large wires to the switched terminals (pins 30 and 87) of the relay. There is no need to run a seperate power wire for relay operation since one of these 2 wires has power when the key is on. We just ran a jumper wire from the wire with power to one of the relay control circuit terminals(pin 85). Then we hooked up the wire from the new GM switch to the ground side of the control terminals on the relay(pin 86). So when the coolant temp gets hot enough, the GM switch closes and grounds the relay which then turns on the fan. I'm making this sound more complicated than it is. Sorry, I didn't have a chance to take pictures.
So far the system has worked great. It is totally self contained and is very simple and reliable. OK enough rambling, here are the part numbers.
Call your local GM or Jeep dealer for current part prices.
General Motors part numbers:
GM fan control switch 3040674
Pigtail connector for switch 12102621
GM relay rated for 20A 25609047 (any common 20a relay will work too)
Jeep part numbers:
Jeep 4.0l 91+ thermostat housing 53006192
91+ heater control valve 56005900
91+ heater hoses 56004783, 52005782, 55036941, 55036942
Also needed:
91+ radiator, 15lb radiator cap, and a generic coolant recovery resevoir. You can get these at your local parts store.
Here is a huge picture of how to route the heater hoses and basic cooling system flow.
Please let me know if you have any questions
Bryan
Well, after doing some digging in the GM parts catalog, I came across a coolant fan control switch for an Oldsmobile FWD car. The switch is calibrated so that when the temp reaches 105*C (somewhere close to 220*F?) its internal switch closes. Now this switch only has one wire attached to it. We used this switch to ground a relay that we installed in place of the original radiator mounted fan switch. This GM switch will screw directly into a 91+ XJ 4.0l thermostat housing(the 87-90 XJs do not have a port for this sensor in their thermostat housing). For the relay, we just cut the wires going to the original switch, then we attached these 2 large wires to the switched terminals (pins 30 and 87) of the relay. There is no need to run a seperate power wire for relay operation since one of these 2 wires has power when the key is on. We just ran a jumper wire from the wire with power to one of the relay control circuit terminals(pin 85). Then we hooked up the wire from the new GM switch to the ground side of the control terminals on the relay(pin 86). So when the coolant temp gets hot enough, the GM switch closes and grounds the relay which then turns on the fan. I'm making this sound more complicated than it is. Sorry, I didn't have a chance to take pictures.
So far the system has worked great. It is totally self contained and is very simple and reliable. OK enough rambling, here are the part numbers.
Call your local GM or Jeep dealer for current part prices.
General Motors part numbers:
GM fan control switch 3040674
Pigtail connector for switch 12102621
GM relay rated for 20A 25609047 (any common 20a relay will work too)
Jeep part numbers:
Jeep 4.0l 91+ thermostat housing 53006192
91+ heater control valve 56005900
91+ heater hoses 56004783, 52005782, 55036941, 55036942
Also needed:
91+ radiator, 15lb radiator cap, and a generic coolant recovery resevoir. You can get these at your local parts store.
Here is a huge picture of how to route the heater hoses and basic cooling system flow.
Please let me know if you have any questions
Bryan
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