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Discussion Starter · #1 ·
Just picked up a 5.9L 123K and it is stock. Aside from CD player in dash it is all original and have some questions can’t seem to get answered anywhere. Not new to Grands just new 5.9s. Hopefully someone can answer or link something that has answer.
1. Upper and lower temp switches for fan control what is the temp preset? By reading gauge I can only guess as to latch threshold. Fan does cycle in and out so it works at least on one speed.
2. Fan control module or direct control through PCM for fan control circuits. Not sure if this has the early WJ module somewhere on it.
2. I would assume cooling package is larger, possibly same size as 5.2?
3. Thermostat? Parts outfits in some cases list “OE” as a 195 with an “OE” alt of 165-185.
At this time it doesn’t have an issue other than now it decided to be a real winter it struggles make temperature( though not sure what that temp is yet). I am just trying to get some basics specs on it for more accurate troubleshooting and to stay ahead of the 23 year old cooling system. Have read up on cooling fan motor/extension harness. Most anything I can salvage forinformation pertains to cooling fan. Thank you
 

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Discussion Starter · #3 ·
I don't know if this will help, but it might get you pointed in the right direction...
I don't know if this will help, but it might get you pointed in the right direction...
Interesting that document header is for 1998 5.9L but document references WJ with E fan. Found a print for fan circuit which covers my application. Working at moment and haven’t dived into circuit yet. The print shows two 5 pin relays, using ground side switching on upper and lower temp switch. Relays are each standalone with dedicated circuit protection giving priority to high temp and A/C switch which share high speed control. Pretty basic circuit. I had assumed it wasn’t PCM driving from I/Os, 1998 wasn’t that advanced. Thank you though! I do this stuff for a living, just got get into their head and see what and why
 

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That was all Mitchell had for a fan theory of operation description. I thought it was weird too how the search for a 5.9 kept bringing up the 4.0 schematic. The main takeaway I got was the latch point of 217°.
 

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Discussion Starter · #5 ·
That was all Mitchell had for a fan theory of operation description. I thought it was weird too how the search for a 5.9 kept bringing up the 4.0 schematic. The main takeaway I got was the latch point of 217°.
I ran across a chart, unconfirmed if it is from FSM that states latch temp on low is 214 and high is 220. I think 214 is little high but I understand why it would be there. If cut in/cut out any lower it would constantly bounce off thermostat. Other issue with this Jeep it started life in BC, was bonded and sold here in US where it has lived southern Idaho all of its life. It an oil pressure in KPA and temp in Celsius , so there is that. Even though have been doing this so long I still can’t translate that in my head well
 

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Discussion Starter · #6 ·
So an update. Connected Matco tooling and found temp reading in Fahrenheit. Broke dash gauge into segments and did the the maths, verified against parameter return from PCM and it is correct. I’m tact it is perfect. No bias in gauge or ETC sensor. Appears by watching run up temp that it has 185 stat in it. Oddly enough fan switch cut in is @ 197-200 and cut out @ 180. I do not know for sure if switches are OEM. Guess could have been charged once and someone did a repin on engine harness, most don’t do that without utilizing cheesy splices though. Regardless other than temp being below the 195 mark everything works so just going to leave it alone.
 

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Nice job. I want to convert my '98 ZJ to an electric fan at some point. I live in Nampa ID and during the summer months the coolant hits 220° or so when in the knarly slow speed stuff. I replaced the entire cooling system last year with a heavy duty fan clutch, it helped a little but I'd still like do do the 5.9 electric fan setup.
 

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Discussion Starter · #8 ·
So I picked this one up in Twin. I know it gets hot there so guessing that is the reason for a 185. Likely had mild overheat condition. Fan diameter seems small and another thing it’s quiet which leads me to think while it flows air is it enough to maintain. The nice thing about an e fan is you can get it to do what you want. There isn’t a shortage of options and configurations for them up to manual override. Vicious fans you are stuck with that, the upside is when clutch is locked it can move large amount of air and being it is engine driven a variable rate at that. Every XJ and MJ I’ve had I immediately hard wired the condenser fan. WJs with 4.0 it was standard (4.7 have both) and I would manually control those also and utilize the viscious even if didn’t have one, I’d put one on. On a larger e fan the most important consideration are alternator capabilities. There is such a high peak draw and sustained current load. I have seen where melted connections and short component life are constant due to just not having the current available. Also would mention that I seem to never see when on the subject of high temps is the transmission. Always here about t-stats, cooling package, water pump, radiator cap, etc…., never hear a mention on trans. The cooler which in design is to remove heat from transmission then air flow can adsorb and remove from cooling package. If trans temp is elevated due to internal issue it will artificially create “overheat”. With cooling package already saturated with engine heat trans temp just adds to overall heat saturation. It can be chicken or the egg for sure, one can influence the other. Just good to keep in mind it’s there and it is a contributing factor.
 

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Discussion Starter · #9 ·
I’ll add one other thing on this subject. Vent the hood. Doesn’t seem like much but it helps scavenge heat esp off rear of engine. Helps with air flow giving a secondary path away from engine bay
 

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I've already experienced an inconveniemt vapor lock condition at the top of a hard climb, hood vents are on my short list along with the WJ fuel rail heat shield kit. As for the fans, electrical load is my primary concern. With the offroad lights, winch, CB etc., I'm already stressing the factory alternator/battery. I plan on installing a larger 130 amp alternator and bigger battery, and larger battery cables. As it sits the winch pulls more amps under full load than the battery and alternator can supply, if electric fans were to kick on during a tug I may have some overload issues.
 

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Discussion Starter · #11 ·
Yeah extra cooling can bite a guy in the ass in winter, but once’s it about 50+ outside there is no such thing as too much cooling. Period. Sometimes I think Jeep missed the boat. Guess they figured suburbia moms and dads were just mobbing to a chucky cheese with the Grands. They didn’t expect us to come along…
 
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