I bought a new jeep couple weeks ago and I've been flushing the cooling system with distilled water. Haven't had any problems til yesterday when I decided to put a new thermostat. The one that I took out was a 160 degrees thermostat so I put the oe 195. When I tried burping the system it started to overheat I thought the thermostat might be bad so I went to Napa to get another and I'm having the same problem. Did I just get unlucky and get 2 bad thermostats. What else could be the problem with it.

 

You can test the thermostat by putting it into boiling water. You should see it open. Take it out and let is cool down, it should close.

Do you have an IR thermometer? Check the temp at the housing outlet to verify the temp. You need a couple of heat/cool cycles to purge the air out.

I have to ask, you did put it in correctly right? Spring side in.

 

Yeah I put it in the right way ive changed it before a couple times on my other and never had this issue. I have the one I put in yesterday I'll try throwing it in and see if it's working. If this one is working I'll assume the other one is also opening and that there is another issue. The old thermostat that I took out the very first time is 160 and it was running around 195 when driving when idling in this heat wave it would get up to 220s with the 195 it's running at 235 almost in red. I'll see if this one I put in yesterday works and if so I'll try burping the system again tomorrow see if I can get more air out

 

The XJ cooling system can be quite finicky and will overheat if the system is not completely filled. Removing all of the air is not enough to prevent overheating. Coolant needs to replace the air that is expelled from the system. I believe it is the latter that causes the most trouble.

The system relies on a very long small diameter siphon hose to the expansion tank/reservoir. This hose can get blocked up with dirt and other trash. It will still pass air and coolant to the reservoir under 16psi pressure (the radiator cap pressure), but will not allow coolant to pass back to the radiator under atmospheric pressure. Radiator hoses may become partially collapsed when the engine is cold. Air can easily be drawn back in instead of coolant perpetuating the overheating problem. The reservoir level does not drop in response to coolant replacing air, so all looks normal. The siphon hose acts as a check valve blocking the flow back to the radiator. Ask me how I know this........

The FSM has no special procedure for refilling the cooling system. They simply rely upon the fact that coolant expands when hot, (pushing out air) and as it cools it will draw coolant back from the reservoir. The image below is from a 2001 FSM, but it is word for word the same as the 1995 FSM. There are steps you can take to facilitate removing air from the system, but the design of the system will do it eventually, assuming all parts are working correctly.

Your thermostat is probably OK. You will need to operate the engine through several heating and cooling cycles, after you verify the siphon hose is not plugged. try to blow through it with your mouth, an air blast from a compressor will make it through, but probably won't clear the clog. Ask me how I know.......


2001 Factory Service Manual

 

You said you are flushing with distilled water. Are you using any type of cleaner? I'm curious if you have a restriction and that's why the PO uses a lower temp thermostat.

 

There is a lot of pressure to ask you how you know stuff in this post.

 

So I did use a prestone flush but that was about 2 weeks ago and it's been long flushed out. The water has been coming out almost clear whenever I drain the fluid. I tested my thermostat and it opened up as long as y'all say it's good in the pictures. I got a head gasket test kit to be sure and tested it the head gasket is good it looks like I let it heat up fully and tested from the radiator like the video said. I'm gonna try drilling a week hole and trying again. I have been letting it beat up and cool down now I have probably done it 4 or 5 times now and it doesn't look like it's pulling anymore water but it's still getting to near red. If the thermostat I tested with a week hole don't work then what do y'all think. Bad water pump? The radiator is brand new aluminum. There is no clogs in heater core or block unless I left small shop towel in there when cleaning housing which I would imagine I would see the blue towel sticking out before I try to put the thermostat in.

 

Are the upper and lower radiator hoses the same temp? How about both hoses for the heater core? Have you made sure that the radiator hoses are in good shape? Not mushy or collapsing causing a flow restriction?

Assuming everything else checks out, then you may have an impeller that is rusting away on your water pump. Although I would suspect you would have seen evidence of that when you flushed it.

Drilling a weep hole in the thermostat won't fix overheating, it's just a nicety to help coolant circulate a little when the thermostat is still closed and help air find a way out.

 

Yeah I know the thermostat won't help I just want to be 100% sure the air escaping. The waterpump looks shiny but I bought a flowkooler. If the waterpump wasn't the issue though and the other things you said are not which doesn't seem to be the case but I'll be sure when I put on the waterpump. What should I be thinking. Could the head gasket be going bad and causing it to overheat without exhaust gasses getting into the cooling system or without the coolant and oil mixing. Just seems a weird that the waterpump looks new and the thermostat was a 160 degree. I'll find out more when I put that water pump on. Also it doesn't overheat more so get up to before the red it hasn't gotten completely into the red

 

It sounds like your overheating issue is likely due to air trapped in the system rather than bad thermostats XJs are notoriously stubborn to burp properly. Make sure you’re filling the coolant slowly with the front end elevated (park on an incline or jack up the front), leave the radiator cap off, and let the engine run with the heater on full blast. Squeeze the upper radiator hose a few times to help purge air pockets. If it still overheats after a proper burp, check for other issues like a weak water pump, clogged radiator, or even a blown head gasket (look for bubbles in the overflow or coolant loss). The 160° thermostat you replaced was probably masking an underlying cooling system problem stick with the 195° and focus on bleeding the air completely before digging deeper.

 

Those funnel kits that are designed to help fill and burp the system are really useful. Lisle makes the one I use.

 

So I put a new flow cooler water pump on and put new hoses. Also added a new belt the other one was kinda bad. I ran it until it almost overheated then turned it off, it sucked up a lot of water so I turned it back on and burned it some more. I'm gonna keep trying to get the air out but if it's not air trapped in there what should I be looking at. I've got a new aluminum radiator, new water pump, new heater hoses and radiator hoses. Been flushing the system everyday with distilled water before I changed the thermostat to a 195. I'm gonna mark the harmonic balancer and make sure it's staying together. What other things should I be looking for. I tested the head gasket and it passed but could it still be bad? Just tried testing again it got up to almost overheating and stops there the temp dropped a little at one point but its just staying within this area

 

1. Is the fan clutch good?
2. Does the electric fan work?

 

If you've confirmed your head gasket is good and everything else is "new" we can go through and test the water pump and thermostat the red neck way. (at your own risk)

WATER PUMP TEST- (also red neck radiator flush)
Cold engine - off
Take top hose off radiator and point it away from your face
Stick water hose in radiator filler neck - turn on and leave running
Start engine and let run until thermostat opens
If water gushes out really fast your water pump works.

THERMOSTAT TEST -
With all hoses connected and system filled turn on engine and leave running
Stand with laser temp gun pointed at thermostat housing
Temp should not get much above whatever the thermostat is rated for and then should be begin to go down some


The above test work best with a beverage in hand and while they technically do work I really don't recommend them.

Anytime I change a thermostat, if it has a jiggle pin I cut the pin out of the hole - if it doesn't have one I drill a hole at the 12 o clock position about 5mm away from the edge with the smallest drill bit I can find. I also jack up the front end at least 6 inches when filling the system to help purge the air. I then top off the reservoir. I have flushed and filled the XJ 4.0 more than a few times and always done it way. After the first heat cycle, when the engine cools, the coolant in the reservoir will be sucked back into the engine and the reservoir level will be down. Just top off the reservoir again and repeat the cycle. After a 2-3 times there should be no air and just coolant and the level correct. As previously mentioned make sure the little hose between the radiator filler neck and the reservoir is good shape - its cheap so just replace it if its questionable.

 

Someone correct me please. But isn't the temp sensor for '95 temp gauge at the rear of the head?

I'd be curious to compare what your gauge is reading to what temp your thermostat housing is. The rear of a straight 6 engine is almost always going to be hotter that the front.

Also, does your clutch fan continue to spin right after you shut off the hot engine? If so, it probably needs replacing.