mjeff87 Posted January 18, 2011 Share Posted January 18, 2011 Been having a problem with the coolant temps in the MJ (for about the last year, actually)....it's running too cool. Changed t-stat last year, no difference. Put another new stat in over the weekend, refilled the coolant and ran it to purge the air out.....it came right up to 190-ish, stat opened and it plunged back down to 120-140 and stayed there. If I let it sit and idle, it comes up to about 180, then drops back down to 160-ish and back up. As soon as i start driving it though, it drops like a rock to the first hash mark on the gauge and stays there, even dips under it if I turn the heat on. All t-stats have been Stant 195 deg superstats.....I can't believe I got three bad ones in a row (???) And I've put two different sending units in it too, same results with either. The only thing I can think of, and it's a longshot, but back when I was rebuilding this 4.0 I pulled the welch plugs and noticed a good deal of crud (chunks, actually) built up between the cylinder sleeves. I spent a decent amount of time cleaning out the inside of the block with scrapers/screwdrivers/brushes and a shopvac. Mebbe I should left all that junk in there :nuts: I've got a heat gun I'm gonna shoot temps with (again) to confirm the gauge reading, but if it's like last time there won't be any difference. For reference, my rig (and swapped in 4.0) are '87, converted to open cooling system with stock radiator and fan clutch, no electric/aux fan installed. I've only ever seen it hit 210 once, and that was back last summer when I was stuck in traffic and it was about 100 degrees out..... Thoughts? Jeff Link to comment Share on other sites More sharing options...
October_V Posted January 18, 2011 Share Posted January 18, 2011 Wow, I just lost my heat too. I was just going to swap in a new thermo, but I will keep an eye on this thread. Link to comment Share on other sites More sharing options...
maddzz1 Posted January 19, 2011 Share Posted January 19, 2011 Mine does the same thing, jeff. Not sure what it ran with the idiot lights, but since I switched the cluster to gauges it always stay right at 155* to 160* (just at or over the line between 100* and 210*) I also have a stant 195* stat Link to comment Share on other sites More sharing options...
mjeff87 Posted January 19, 2011 Author Share Posted January 19, 2011 every living-breathing fiber in me says "therm-o-stat", but I can't come to terms with that diagnosis..... I'm gonna run it some more and cycle the 'stat, mebbe it just needs to find it's happy place after a few heating/cooling cycles. I dunno :dunno: Link to comment Share on other sites More sharing options...
maddzz1 Posted January 19, 2011 Share Posted January 19, 2011 I was thinking maybe the stat slid a little during assembly since I didnt remove the serp belt, but I think it would leak if that was the case. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 19, 2011 Share Posted January 19, 2011 Did you try testing the stat on the stove in a pot of boiling H20 and a thermometer? I've never liked Stant thermostats (had similar problems) and always use the OEM 195* thermostats from the stealer. Link to comment Share on other sites More sharing options...
jimoshel Posted January 19, 2011 Share Posted January 19, 2011 I always use the hotwater trick but without the thermometer. Water boils at 220*f. at sea level. Most thermostats are 190-195. Place the thermostat in a pan of water, insuring it's completely covered. Place pan over open flame, or electric plate. Thermostat should open before water starts boiling. Not as accurate as a thermometer but will tell you if the 'stat is working or sticking. Link to comment Share on other sites More sharing options...
Akula69 Posted January 19, 2011 Share Posted January 19, 2011 The guy over at the Gojeep site had a similar problem, and solved it by putting a flow restrictor in the radiator hose (a piece of hard plastic with a smaller hole drilled in the center). The link: http://gojeep.willyshotrod.com/HowtoRadiatorRestrictor.htm Good luck! Link to comment Share on other sites More sharing options...
mjeff87 Posted January 19, 2011 Author Share Posted January 19, 2011 I played hell getting the housing to seat properly this time around, with the stat "slipping" out of position. Ended up using some silicone to keep it seated whilst I used all three hands I had repositioning the gasket/housing (with serp belt removed). Actually ended up doing it 3X cause it leaked from the bottom bolt the first two times. Turned a 1 hour job into a half a day and made a total mess out of my garage :fs1: I can tell the stat is "working" so to speak, as it cycles from about 180 back down to 140-160 if I let it sit and idle. Maybe I'll pick up a MOPAR unit and see how it does. FWIW, on the last one I drilled a 1/8" hole in the outer ring to help purge air/steam, this time around I didn't. No difference. Link to comment Share on other sites More sharing options...
mjeff87 Posted January 19, 2011 Author Share Posted January 19, 2011 The guy over at the Gojeep site had a similar problem, and solved it by putting a flow restrictor in the radiator hose (a piece of hard plastic with a smaller hole drilled in the center). The link: http://gojeep.willyshotrod.com/HowtoRadiatorRestrictor.htm Good luck! Very intersting.......I may investigate that. Doesn't solve the mystery of why a completely stock cooling system doesn't work, but if it solves the problem temporarily while I can ingest large amounts of beer and think out the cause I can live with that :cheers: Link to comment Share on other sites More sharing options...
Eagle Posted January 19, 2011 Share Posted January 19, 2011 Thoughts? How's your heat? Not "temp" ... "heat." The temp gauge in my '88 XJ has been reading consistently at the first hash mark from the left for at least 5 or 7 years. I've gone through several thermostats and three temp senders ... doesn't make any difference. Then I realized that my volt meter also reads low, and that's been verified by checking the voltage at the battery. As for the temp -- I have excellent heat, even with the outside temperature below 20 degrees, and if the coolant temperature was really what the gauge says, I'd be shivering while driving. I suspect your gauge may be off. I also suspect ... but I've been too lazy to check into this ... that the erratic gauge readings may be due to a bad ground between the gauge cluster and the chassis. Link to comment Share on other sites More sharing options...
mjeff87 Posted January 19, 2011 Author Share Posted January 19, 2011 heat is so-so.....I remember it being much hotter back when it was a 2.5L. So hot that I kept the temp lever about 1/2-3/4 toward "hot". If I set it to full "hot", it was too hot inside the cab. Link to comment Share on other sites More sharing options...
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