Keeping My Cool

Time for a new post updating my cooling situation. See the previous post for more information if interested. Two things were left on the table to do, those were coolant flush and auxiliary fan override switch.

No pictures of the first item, it was pretty much just a boring process of filling and draining the radiator. I went with a fill/run till warm/drain/fill/run till warm/drain...repeat ad nauseam method using the cleaner you leave in your radiator for 3-6 hours of runtime. No particular reason but after about the 5th cycle I was wishing I had done a simple power flush. For the first couple of drain steps, I also ran some water through via the hose that connects to the top of the thermostat housing...a little mini-flush if you will.

The first cycle was very dirty, so I accomplished a little bit at least. The second cycle was cloudy with each subsequent cycle get more clear. The 4th cycle looked pretty nice, so I switch from tap water to distilled at that point. I basically put a total of 5 gallons of distilled though the system with the final cycle leaving about 1.5 gallons of distilled in the system to which I added the antifreeze to top the system off. Ended up with about 55/45 water/coolant mix.

Unfortunately the new coolant by itself didn't really solve anything. After enough time sitting at idle the motor still gets hot enough to kick on the auxiliary fan. It did seem to possibly cool it down quicker than before though...no hard numbers on that though. But again, it was needed maintenance so no real loss.

So, given that when both fans are on pulling air through both halves of the radiator the cooling system seems capable of keeping the temp in check, it seems to me that the answer is to be able to turn the cooling fan at will. I found some instructions and set to work making the modification. The basics of it is that the PCM brings a wire to ground when it want to trigger the fan, so we splice into that wire and put it to ground with our switch.

First I found the magic wire in the PCM wiring harness. I just stripped back a little of the insulation and looped another wire around it and then stuck a huge ugly glob of solder on it to hold it tight(need new soldering iron tip...at least that's the excuse I'm going with). A quick test of turning the key in the ON position and touching that wire to ground showed that it indeed works as the fan kicked on...

So that leaves me just in need of a switch. After brainstorming a bit, I decided to raid my computer graveyard in the attic and pulled a switch from an old power supply. It fit perfectly in the small section at the top/bottom of the filler panel to the right side of my instrument cluster in my '96.

Only drama here was getting the instrument panel bezel off. It was tight...I'm probably missing some trick, and I need to figure it out before I take it off again...

All was well until a couple days ago when I noticed the Jeep not warming up again...the failsafe thermostat had apparently tripped. I'm not sure what the triggering condition is, but I decided I would rather deal with a normal thermostat failing closed once in a blue moon versus the failsafe tripping every other day, so I just replaced it with a normal one. Problem solved.

Tested out my fan and it worked great. Played around in the yard and let it idle for 30+ minutes and with the fan on the temp guage was steady on 195. Still have to see how it reacts in the summer heat, but I feel good as of now. My only problem is that the switch ended up throwing a CEL because the PCM doesn't like that wire being grounded when it's not expecting it. I've found a fix involving a relay that will be my next little project.