thedave360 Posted August 12, 2013 Share Posted August 12, 2013 Hi! Been a while since I've been on the forums. I've been busy putting my rebuilt motor back in the MJ and putting some break-in miles on it. I have some questions about cooling though. What is considered a "normal" temp range?? 210-220? Lower? Higher? Here's why I'm asking... I had a local shop who sells remanufactured engines re build my 4.0 (long block). I finally got it back in and its been running a bit warm. I'll go drive it for a while (15-20miles) and when I sit and idle for a while, the temp would jump up to about 225-230 and the aux fan would come on. It would take a while to cool down back to about 210 then it would creep back up and just keep cycling like that until I started driving again. When driving at highway speed it would stay well above 210 unless it was raining...then it would drop well below 210. I've got a little less than 1000 miles on it at this point so I've been trying to fix the cooling issues. I started with the easy stuff, doing a chemical flush on the system. This seemed to help but it was still having issues. The coolant that originally came out looked like chocolate milk. I flushed it enough to get to a nice clear green when I drain it now. After doing that, I went to replace the thermostat. Only to find out that I hadn't installed one when I put the front of the motor together :doh: . I got a stock 195degree. That didn't help at all. It now warms up quicker...which is the job of the thermostat. But after it warms up, it doesn't start to cool down until the aux fan comes on. So I started reading forums..... Thats when I decided, it would probably be a good idea to get a new radiator since the original one had that chocolate milk running through it for so long and is probably corroded past the point of no return. And, I might as well get a new fan clutch, since the one I have is as old as the truck (92). So I bought an all aluminum 3 core radiator (and boy is it shiny! :brows: ) along with a brand new zj fan clutch. After an afternoon of squeezing and praying it would all fit, I filled it up and cranked it up. Seemed to work ok. At a cold start, temps get up quick, then I can see when the thermostat opens and the temp gauge drops about 10 degrees really quickly. I go for a drive, it gets to 210 and sticks there while I'm driving. If I stop though, the temp starts to slowly creep up. It takes a while, but eventually, the aux fan comes on to cool it down. When that happens it goes down quickly, then the fan goes off and it slowly creeps back up again. With the new radiator, it holds temp MUCH better while driving, and takes a while to heat up when idling and cools quickly once the fan comes on. Am I missing something? Or is this normal and I'm just being paranoid? Any advice would be helpful. --Additional Info 92 4.0 HO. stock, rebuilt recently. All new sensors including temp. Running "break-in" oil with zinc additive. (to be changed out soon for normal) Link to comment Share on other sites More sharing options...
Eagle Posted August 12, 2013 Share Posted August 12, 2013 210 is normal if your gauge is reading somewhat accurately. Running cooler in rain is a clue. The thermostat is there to keep temps UP, not down, so when the temp starts going higher than the thermostat rating it indicates a problem. The fact that your radiator can shed heat better in rain than in dry air strongly suggests that your radiator is not up to the job. Link to comment Share on other sites More sharing options...
thedave360 Posted August 12, 2013 Author Share Posted August 12, 2013 210 is normal if your gauge is reading somewhat accurately. Running cooler in rain is a clue. The thermostat is there to keep temps UP, not down, so when the temp starts going higher than the thermostat rating it indicates a problem. The fact that your radiator can shed heat better in rain than in dry air strongly suggests that your radiator is not up to the job. Excellent. That makes me feel much better about replacing it. With the new one, coming home yesterday in the rain, it didn't seem to affect the temp very much. Any thoughts on getting hot enough to trip the Aux fan while idling after a long drive? Link to comment Share on other sites More sharing options...
Eagle Posted August 12, 2013 Share Posted August 12, 2013 Any thoughts on getting hot enough to trip the Aux fan while idling after a long drive? That's normal in hot weather. Link to comment Share on other sites More sharing options...
thedave360 Posted August 12, 2013 Author Share Posted August 12, 2013 Ok, I can live with that. So as long as the temp doesn't keep going up when the fan kicks on, I'm good right? Link to comment Share on other sites More sharing options...
jeepsouth Posted August 12, 2013 Share Posted August 12, 2013 A new radiator was the biggest help in getting my mj running cooler. Removed the original just last year. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 13, 2013 Share Posted August 13, 2013 Have you replaced the fan clutch? Got a shroud on the mechanical fan? Link to comment Share on other sites More sharing options...
thedave360 Posted August 13, 2013 Author Share Posted August 13, 2013 I replaced the fan clutch with one from a ZJ because its supposed to move more air. I do have a shroud but its missing a section at the bottom. Probably should get a new one. Link to comment Share on other sites More sharing options...
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