1990 XJ 4.0 Overheating

[JeepinJim]

My 90 XJ is overheating and I’ve done the norm like changing the thermostat, checking for leaks, hoses, etc. Anyone have any ideas? My next step is to flush the system and make sure nothing is plugged, like the heater core, etc.

 

[DonnyG]

Ask Nomad about this one. It may be worth it to remove the radiator and completely hose out the fins. His was pretty much plugged solid. Caused much discontent.

 

[JeepinJim]

I've thought about it might be air-bound, but it's not your typical radiator, it's doesn’t have a cap. Close system with a reservoir bottle against the firewall.

 

[beaker]

Parking it facing down hill while your burping it will help too. Those years are very difficult to get all the air out.

 

[Erik S.]

To purge your XJ's cooling system, and this came from 2 well respected Jeep mechanics, remove the heater hose from the thermostat housing. Pour coolant into the overflow bottle until fluid starts to come out of the t-stat housing. The t-stat housing is the highest point in the system, and it will be completely full. Fill the overflow bottle to the appropriate level.

This is quicker than waiting for it to burp itself.

Before you say "well the t-stat won't be open, cause it's not warm", take a look in there, there is a small bypass to the heater hose.

Not hard at all to get all the air out, just gotta do it correctly.


Erik

 

[JeepinJim]

Thanks everyone! Some good ideas and I'll give it a shot this weekend.

 

[JeepinJim]

Well, I think if worked for the most part. It still get's pretty hot and the resivor starts to vibrate and shake. I think I might have overfilled it. Now that I know most of the air is out and it's been sitting all day, I should make sure the fluid level is correct and go from there. Thanks everyone for your help.

 

[kvjp97]

My XJ started to do that also I did the norm and I couldn't figure out what it was. I just resorted to the fact of keeping the defroster with heat on in my truck, never overheated after that! Granted that's not the best solution but it was a 91 XJ beater so I didn't have a problem with it especially in the winter time.

 

[sidriptide]

under what conditions is it over-heating? and what temp is it getting to? 

at idle a bad fan-clutch will let the temp run up.  the  proper fill level for that reservoir is pretty low actually. look inside the fill hole when its empty or at least low. there is a short vertical "post" right there. the top of that post has a notch/step cut out of it for the top 1/4" or so.  the COLD fill level is up to the step. NOT above it.  there is alot of coolant in the system and that bottle is strictly to purge air and allow for expansion.  the full-hot level is roughly 50% of the bottle. 

 

[JeepinJim]

Thanks for the tips.  It's much better now that I flushed and purged the air.  It Runs around 200 all the time.  Sometimes below, but not usually.  The clutch fan might be an idea.  I haven't looked in to that.  It's drivable, but I'm always looking at the temp.

 

[JeepinMaxx]

Blame it on the 'closed loop' cooling system :evil:  Later XJ's switched to the 'open' system which had a radiator cap and puke tank.  Unfortunately, my wife's old '90 XJ had the closed system and it overheated pretty easy.  I think it can be swapped.  BTW - previous advice is correct - if the temp sensor is bad - the axillary electric fan won't come on unless the AC or defrost is on.  Quick fix is to run a fan switch to bypass the sensor.