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T-stat issue?

B

Bdiddy11

NAXJA Forum User
Location
Boise,ID
First off I have a 87' Cherokee Chief, automatic....Ok... sooo... this past weekend I went camping with my wife and some friends. Long story short, I went up a hill and 3/4 the way up it turned into really loose dirt and was rather steep... Jeep slides back and I get caught up on a stump...so I try going forward getting off the stump, no worky, try it a couple times different ways and the Jeep overheats and so I pop the hood a little to let it cool out and it just starts smoking something fierce and coolant is shooting out the bottom like there's no tomorrow... so... the next morning we go up there and I hack at the stump with an axe for about 3 hours... it was more than a foot in diameter... get the Jeep down finally back to our camp and it starts getting hot again. So, we take the radiator hose off and there is a large leak where it burst due to pressure (i'll get a pic of it) and so luckily my father in-law had a spare radiator hose but for his F250... so we cut it down a little to work with my Cherokee.

Drive home and it's doing fine... the next day (Monday) I get home from work and it starts leaking near the coolant bottle. After about 15-20 minutes of driving the temp gauge creeps up past 210... I ran a test yesterday, put some water in the coolant bottle to the line... ran the Jeep for awhile, started getting hot, got to 210 so I turned off the Jeep and watch the coolant bottle... the top hose that spurts it back in just keep spurting it in and doesnt stop... the bottle eventually fills up almost to the cap and is bubbling bad so I slowly open the cap to relieve some pressure... I asked my dad what might be wrong and he said it might be the t-stat not operating the way it should. I'm hoping that's the problem since it'd be fairly easy to fix. Anyone have some input on this? I checked the hoses... no holes and all are tightened properly...
 
As well as a possible problem with the t-stat it may be that you a significant amount of air in the closed system. Also, if it was leaking near the pressure bottle you may have developed another leak there while all this was going on. The bottles commonly develop cracks in the main body of the bottle as well as around the inlet and outlet.

Try to burp the cooling system to get the air out, and don't use straight water.
 
It's not the bottle... I took it out, looked at it, put water in it to look for a leak... it's a new bottle. It's only been in there for about 5 months or so. How do I go about burping my cooling system? And when you say don't use straight water should I put some coolant in with it as well? Thanks again. If anyone else knows what might be the problem please chime in.
 
OK, you said it was leaking "near" the pressure bottle. So the only other things that would be leaking in that area are the hose connections to and from the heater core OR the heater control valve (it's the little doo-dad with the vacuum line attached). But enough about that leak.

Do a search on here as to how to burp the system but this is how I've done it in the past before I switched my system over to the open system.

To burp the system you can start the Jeep when cold, unscrew the coolant sensor at the back of the head until coolant comes out, then screw it back in, tight, OR start it with the pressure bottle cap open and add a little bit of 50/50 antifreeze/water mix at a time. Let the system cycle it through. Keep adding the 50/50 mix (don't let it run dry cause it'll just suck more air in). When the beast starts warming up it'll circulate more coolant through the system, keep adding coolant. When it stops taking coolant after about 15 minutes. Put the cap back on. Then add some more for the next few days if needed. Don't open the cap when hot.
 
If you run just straight water, there's a increased wear on the water pump. Could cause premature water pump failure. If that impeller grenades on ya, it could cause big problems.....water pump is directly in front of #1 cylinder wall
 
What i did with mine, i found through trial and error. It was my first time dealing with a closed system (i'd always driven old V8s before) and I was at a loss! I'd fill it up, start it and it would overheat! Turns out with mine, it liked the following procedure: Fill up the bottle to the top, start Jeep. Let it idle 10 min or so, turn Jeep off. Wait a bit, then crack the cap off the bottle. It would then appear to "drink" the contents of the bottle, allowing room to add more coolant! Do this 3 or 4 times or until you pop the cap off and it doesn't start gulping the coolant down. Replace cap, and drive! Hope this helps man.
 
Okie... soo...T-stat has been replaced... It stays at a good temp (180-210) once it's warmed up all the way. The problem I now face is that the resevoir bottle itself just keeps taking in coolant until it's all the way to the cap...Once I turn the car off it kinda bubbles in there and doesn't really go down... unlike before where it kept bubbling lots more and came out the cap more. I purged the system twice already... unless I did it wrong and didn't get all the air out? Anything else that could be causing the bottle to no cycle through the coolant and just have it keep building up with the t-stat staying at a good temp? Thanks.
 
I hate to be the one to say this, but it could be a sign of a blown head gasket. If the gasket is damaged between the combustion chamber and the water jacket, gases could be escaping into the cooling system and building pressure.

Are you noticing any white smoke from the exhaust?

Chances are there is still are in the system, and it needs to be bled out.
Jack up the rear and remove the temp sending unit from the top of the head. Fill from theat hole until full. Replace the temp sender. Then pull the top heater hose from the heater core loose...but not off (just make sure you can take it off). Start the Jeep and let it get to running temp and with a good glove (I use a thick rubber glove) start to pull the heater hose loose-but not all the way off. Let the pressure in the system push any remaining air out. Then replace the hose.

Using this method you should get all the air out. The air usually builds up in the higher parts of the engine (heater core and top of head). Watch your coolant bottle and top it off when needed.

Good Luck!
 
Sounds like the cap is bad, or cross threaded, not holding pressure. If not the cap, could be early signs of a head gasket leak, or could still be air in the system.

Personally I just ran mine with the cap off, turned off the jeep if the coolant got to hot and too high in the bottle right after putting the bottle cap back on.

Then after it cooled, I removed the cap, added more 50/50 mix to the bottle if it was low again and repeated the procedure. That was all I did to mine (87) to bleed it after replacing the radiator and hoses.

You are using antifreeze right? If you are using straight water that is your problem, it is boiling.
 
There is no white smoke from the exhaust... how much does a new head gasket cost and are they hard to install or no? I don't really have mechanic experience...

Ecomike, I am using 50/50 anti-freeze... I was thinking it was the cap, went to a local Jeep only shop and told the guy my problem and said it was air in the system and couldn't be the cap at all... he was a jerk while telling me this too... If it's the cap I'm soooo going to laugh at him (at leat to myself) I noticed that the rubber ring on the inside of the cap is kinda funked up... like it's not sealed to it completely... there's some parts of it that I can see a small gap. Could that be the cause?
 
Bdiddy11 said:
There is no white smoke from the exhaust... how much does a new head gasket cost and are they hard to install or no? I don't really have mechanic experience...

Ecomike, I am using 50/50 anti-freeze... I was thinking it was the cap, went to a local Jeep only shop and told the guy my problem and said it was air in the system and couldn't be the cap at all... he was a jerk while telling me this too... If it's the cap I'm soooo going to laugh at him (at leat to myself) I noticed that the rubber ring on the inside of the cap is kinda funked up... like it's not sealed to it completely... there's some parts of it that I can see a small gap. Could that be the cause?
Click to expand...

You definately need to replace the cap. Keep in mind you MAY have more than one problem, but from your description the cap is toast for sure. The rubber gasket should be smooth and flat with no bends or folds and no stress/age cracks in the surface of the rubber. Also the spring tension inside may not be holding enough pressure, the area you can not see.
 
Ok... I figured it might have been the cap cuz when I looked at it the rubber ring wasn't completely flush... Know where I can get just the cap for a decent price + shipping? Would the dealership be best? I've been trying to find a place online... cheapest i've found so far is $10 or so total with shipping...
 
Bdiddy11 said:
Ok... I figured it might have been the cap cuz when I looked at it the rubber ring wasn't completely flush... Know where I can get just the cap for a decent price + shipping? Would the dealership be best? I've been trying to find a place online... cheapest i've found so far is $10 or so total with shipping...
Click to expand...

# 52006707 at www.4wd.com/cherokee is $4.99, bottle with cap is $26.99.
 
I had the same problem a while back, got an OEM cap for less than 10 bucks, AND an OEM thermostat.
I had a napa thermo in it and there is a little pressure equalizer hole in the OEM thermo that gets mounted with the hole at the top.
Been working fine since.
It boiled and spit all over under the hood when it happened, and did put some visible stress marks on the bottle...
 
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