Overheating Issue

[JeepFanactic]

I have a 1987 MJ 4.0 5 spd with 88k on it with the closed system.  Today stupid idiot light came on for the temperature gauge.  I didn't see anything leaking.  Anyone have any suggestions what it might be.  Is there a way to test the closed system so that I don't have to throw parts at it. I know it can be anything from water pump, radiator, thermostat.  Do the sensor have a tendency to go bad.

[BryceOJ]

Funny seeing you having the same problem I'm having with mine right, and were both in VA.  Mines been over heating too.  Havent tried anything yet.  I pulled the thermostat, tested the old one and it didnt open up at the specified temperature.  I then went and got a new one, and while installing it the thermostat slipped as I tried bolting the thermostat housing thing back on and the housing cracked at one of the ears near a bolt.  So now waiting on a new one of those.  But for the old one being stuck, I believe that my problem was a stuck closed thermostat.  Ill get back to you on if it fixes it when I get my part in.  

 

I'm not a mechanic nor skilled with working on vehicles,  I'm 20 years old and been working on my comanche which initially never started but fixed it and got it to run, and been learning how things work by that.  You can do some easy checks to try and pin point why its overheating though, things I found while searching why mine was overheating.  If its not leaking anything, are you still losing a lot of coolant?  You can check your oil and see if its kind of milky looking, which means that oil and coolant is being mixed up, which means theres a possiblility that your head gasket blew, or the head is cracked.    I see all youve described is that your temp light came on, was you engine compartment smoking or anything, or did your engine cut off from overheating?  hopefully I'm a bit of a help to you.  replied to you to show some empathy since we are in the same boat.

[87MJTIM]

Now that winter is through and temps are rising, does it happen when you are sitting and idling or doing a lot of stop and go?  The colling fan may be bad.  Test it by making a jumper to the battery.

 

Also, check the coolling fan relay on the drivers side, in front of washer fluid bottle.  (Search youtube for how to test a relay.)

 

Or, check the radiator temp control switch  http://www.partstrain.com/store/??N=0&Nr=AND%28universal%3A0%29&PN=0+6004&VN=4294967148+4294962346+4294962302+4294963082+4294966684&domain=partstrain.com&Nr=AND(universal:0) 

[nitroxsteve]

Nothing is different about the closed system except you don't have a radiator cap. Like 87MJTIM said what were you doing when it overheated? How did you get it to cool back down? Could be anything from the thermostat to a bad fan clutch. We just need a little more info.

[cz777]

 well i had other Critters  had overheat troubles, water pump can have bad impellers like rusted apart /falling apart etc bad  radiator plugged up /bad cap  /bad hoses  coolant bring bad ..  .....its a flow pattern follow the flow from radiator to engine and back  

[sloride]

My '88 did the same thing at about the same mile mark as your MJ.  It turned out the sensor for the electric fan went bad.  Replaced it and its been good......  Oh, there was one other time that light came on.  It turned out the bottle had a crack in it and was leaking radiator fluid.  That crack happened before the sensor if I recall.  We're talking 15yr time frame here.....

[banshee]

Don't forget to check

Your clutch fan