Overheating Troubleshooting

Lets begin by saying that I haven't had any other overheating issues the the 3.5 years I have owned the vehicle. Set up: 98 AX15, 35's, 5 in of lift, roof rack, winch bumper w/o winch (so not THAT much extra weight). 135k miles on it. I drove it to Moab and back last year w/o any problems.

Now to the history. The Jeep used to run at 210 flat, didn't matter what I did. But over the past past 5 months or so I have noticed that is has started to creep up to 212 and then 215 etc. Didn't think a whole lot about it but I did notice. Then the other day after about thirty miles of highway driving (75 mph) I noticed my temp would shoot up to 245 for about 5-10 seconds and then go back down to 217-220. This spiking happened about 4 times before the top radiator hose blew. Replaced that and got the fluid flushed and replaced. Then today I was driving highway for 20 min (75mph) and had the fan on but not the AC and the temp slowly kept creeping up from 210 to 218ish and then the same spike happened like before only this time I pulled over so as not to blow a hose. The coolant in the reserve was boiling over...(I had shut it off and then put the keys in the ignition to check the temp and I think the boiling over started then) After that I drove 60 mph (then 55) for the rest of my trip to Denver and stopped once or twice. I had the heat blowing full blast and the temp still was nearing 220 (I would try to not let it get there as that was when the spike seemed to happen).

My diagnosis is that the thermostat is not functioning properly (shoulda had it repalced with the flush, oh well) but I really dont know because there is so much that can be wrong. What do you guys think? Thanks for your input!

I would start by replacing the radiator cap, Then I would replace the thermostat.

-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time due to neglected maintenance and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant


.

Good list above. Of the various things I did to combat this, water pump by far made the biggest difference. When I pulled the existing pump, it showed no serious signs of corrosion as in the pic above, but when the new OEM was on, clear difference.

Thanks a lot, hopefully I wont have to go through the whole list! But I will start with the thermostat and giving the radiator a good cleaning.

Space_Monkey just posted up about this exact (well, almost) same thing.......

Go here:

http://www.naxja.org/forum/showthread.php?t=1068298

Read post #17 to see how he fixed his..... HTH!

Similar but not the same, he had a fresh radiator and thermostat (mine are not), his situation and symptoms were slightly different. I had read that thread. Thanks for the heads up!