Adding an electric fan to a non A/C truck. 1992 MJ 4.0 H.O.

[FrankTheDog]

My 92 didn't come with the Electric fan. There was a fan wire tied to the main harness with some tape, I cut the tape and plugged it in to a working fan. I added the relay and a fuse to the PDC in the proper place. The fan still doesn't come on when it comes up to temp. What am I missing? With the weather getting hot, the truck is starting to run to close to the red while in traffic for my comfort.

 

I'm contemplating running a switch from the dash to a relay to power the fan. I have the power/comfort switch and a cargo light switch that I can put into my dash from an 88 MJ to power the relay.

 

Any other ideas? Thanks. :wrench:

[HOrnbrod]

At 230* or so, the aux fan is triggered ON by a ground signal from ECU pin 31 to pin 5 of the aux fan relay in the PDU. It's a BLU/PNK wire in the 91-92. Perhaps in a non-AC vehicle that wire is not in the harness. You can control the fan manually by applying a ground to the PDU relay via a dash switch as you mentioned. Send me an email address and I'll send you the wiring diagram if you want.

[vaquaro]

Another option is a adjustable thermocouple switch/relay . I used "Flex-o Lites" pusher fan with thier adjustable switch/relay and it works flawlessly :thumbsup:

[FrankTheDog]

Well I replaced the whole cooling system on my truck.

I found that I probably don't really need the aux fan on it.

 

One of the previous owners put a cooler thermostat in it and the temperature gauge was going from about 180 to 250. I put a new radiator, (the original one was still in it, it was toast) water pump and thermostat (OEM 195) in it. Got all the air out and the gauge was reading about 240-250 steady. It didn't act or feel that hot so I grabbed my brothers

IR thermometer and scanned the engine, 210 at thermostat housing, 235 on head above the exhaust ports and 175-180 around the sparkplug hole. So no worries, I just have an inaccurate gauge.

 

Is there any adjustment on the gauge?