Okay so for the past month or so my heat has been blowing luke warm but not hot like it should even once the jeeps heated up to temp. I put a new 195 thermostat, new water pump, upper rad hose, and radiator in two years ago when I first got the jeep becuase it was having an overheating issue and the old rad was filled with sludge. So I installed all the new stuff put a back flush kit on an flushed it till it was crystal clear no sludge nothing. Heat worked great no issues until a month ago. So I checked under the rad cap and its sludge again. So i figured it needed flushed again, not sure why its building up sludge. Its no my dd anymore so I put it off until today. I drove it to the store to get some coolant and on my way there the heater air started smelling like coolant but it wasnt overheating no issues so I parked it and when I shut it off coolant poured out of the rad cap and I noticed the overfill bottle was half full. So I got my coolant and figured somthing was plugged so I was going to limp it home flush it and everything would be fine. Got about halfway home, heater started blowing cold air, temp shot to 260, i was only about 4 min from my house so i was just gonna try an baby it the rest of the way. made it about 2 more miles engine starting sputtering like it was gonna stall so i pulled over quick just as i did smoke started pouring off top of rad and valve cover so I shut it down. Checked under the hood the upper rad hose felt cold bottom rad hose looked like it was smoking couldnt really tell though, rad cap was hot. other upper cooling lines didnt look over expanded cant remember if they were hot or not dont think i checked. So i let it cool down to 210 an limped it the last mile home pulled in the drive started sputtering again so i shut it down and there seemed to be just alittle bit of smoke coming out of the grill beside drivers side headlight.

I have no idea what the problem is or where to start, im afraid to start it an try to flush it because if somthings plugged an the engines getting no coolant I dont want to screw it up worse than I already might have. Ive been reading a couple threads and Im thinking the issue might be a bad thermostat and or rad cap but Im not sure. So any help with this would be greatly apprectiated.

I also did just replace the serpentine belt a week ago and made sure it was tight enough so i dont think theres an issue with it not turning the water pump pulley because I put about 50 miles on it right after doing the belt and there were no issues besides luke warm air when the heat was on

 

2 years ago, did u fill it with just water or a 50/50 mix of coolant/water? During that 2 years, did u remove the rad cap and inspect coolant color/level?

 

I did a full flush then filled it with 50/50 mix. And since then I checked it a couple times and it's been getting progressively more sludge build up. More so after this past winter. Because it had no issues and good heat this past winter. I'd been meaning to flush it again but never got to it, school and work got in the way and it hasn't been my daily driver since spring, i drive it maybe 100-200 miles a month if that.

 

I did lose the upper rad house sometime in June and lost alittle coolant and replaced the little I lost with distiller water since it was summer. That's part of why i wanted to flush it before this winter so that I could make sure the mix was right so it didn't freeze

 

Distilled water will dilute the coolant's corrosion protection just like tap water will. Any iron block motor needs plenty of corrosion protection and kept completely full. Coolant should be flushed/changed at the 1st sign of a color change. If coolant level is not maintained to the top (air in the system), rust/corrosion will start to form quickly on internal areas exposed to air.

 

okay, well im still not sure though as to whats causing this overheating issue. I pulled the thermostat today and put a new one in. When I took the old one out I tested it in a pot of boiling water and it seemed to be working fine. I opened the drain valve on the rad and disconnected the two heater core hoses from the thermostat housing and ran water through the rad from the cap until it drained out the bottom clear. After running the hose through the rad eventually water started coming out of the thermostat housing as well but im guessing thats because the upper rad house was still attached. I tried to backflush the heater core by putting the hose into the top heater core hose and letting it flush out of the bottom hose but I couldnt get and water to go through it was just sprayin out from where I had the hose at. Probably because I couldnt get the hose actually into the upper heater core hose because my sprayer attachtment for the hose broke off. Im gonna go get another attachment for my hose tomorrow and try to force water through the heater core to unclog it because im pretty sure thats the issue. Could a clogged heater core cause the motor to overheat?

 

To do a proper flush, u need to disconnect the the heater hose and rad hose from the t-stat cover and disconnect the bottom rad hose from the water pump. Stick the garden hose into the heater hose and flush. Stick the garden hose into the heater hose nipple on the t-stat cover and flush. Stick the garden hose into the top rad hose and flush.

With regard to a plugged heater core causing overheating.....no, technically it shouldn't. However the heater core on '97 up XJ r always part of the "coolant bypass loop" and if the heater core is plugged solid, coolant will not flow thru the block and head thus possibly causing an overheat until the t-stat opens allowing the "coolant radiator loop" to come into play and cool the motor.

A poorly maintained cooling system can plug even a new radiator in 2 years. Just because flush water flows clear doesn't mean that solid internal scale/sludge hasn't formed inside the small radiator passages/tubes. Solid scale/sludge can't be flushed out.....it must be "rodded out" and a radiator has to do that.

 

I'll try your method of flushing today, the weathers nice for once in pa haha, but a two days ago I flushed it using my backflush kit from prestone that's on my upper heater hose followed the instructions per the kit. I also opened the drain valve and ran the hose through the rad. But I'll try your method when I get home. Now I had also heard somthing about removing a drain plug on the side of the block but some people were against it and said that it causes leaks etc. and how do you "rod" the radiator to remove any debris? I might just get a champion all aluminum 2 row rad after Christmas and a flow kooler water pump.

 

Oooops, my bad.....my post should read a radiator shop can rod out a radiator....the radiator is taken apart.....tanks separated from the core. The core is what is "rodded out".

Do your homework regarding an aftermarket rad. If the core is not thicker than OEM rad, nothing is gained. I doubt a 2 row is twice as thick as the OEM 1 row. Don't be fooled by advertising hype....do your homework and compare specs.

 

It's all good, and ya il have to do some research, but do you think I should remove the drain plug on the side of the block, think I've heard em called freeze plugs, and clean out the water jacket or no

 

I've heard removing freeze plugs just can cause more leaks in the end and they snap off often

 

The freeze plugs r not drain plugs.....if they r not leaking, don't touch them. There r small screw-in drain plugs on the drivers side of the block.....I wouldn't touch them either. The block doesn't hold much coolant, not worth messing with removing the screw-in drain plugs, especially if u jack the rear up with the bottom rad hose removed from the water pump.

 

Quoting this because it bears repeating. I did this over the summer and got so much crunk out of the block, radiator, and especially the heater core, it wasn't even funny. I'll see if I can dig up a pic.

Edit: Here's what came out of the heater core. Yummy.

 

I flushed all of my jeep... Wow the stuff that came out. My heater core was the worst part (reason I flushed everything heat sucked) the water would run clear then it would kind of choke and sputter up and it would be brown and green with chunks...(nasty I know) This happened like 5 times, and I flushed everything probably 6 times after the water came out clear just to be sure it was all good.

 

Sounds like chunks of sediment breaking off as the water washes through the core. Mine was similar sans chunks. Just nastiness with brief periods of clear water in between.