Coolant leak (boiling reservoir tank)

1998WranglerTJ

1998WranglerTJ

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Mar 9, 2023
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Phoenix Arizona
Hey y’all,

Being doing some work on my 1998 wrangler. 74,000 miles. Went to pickup a warn winch today and after about a 25 minute drive in the AZ heat, I pulled over and could hear some hissing and smelled coolant. Had two hoses leaking. I have a reader plugged in and has been driving at 210 and gets up to 225-230 on highway speeds.

I top it off, pick up the winch, and head back home, keeping on eye on my temp. Highway stayed at 230 cruising and never above. Back to 210-215 on streets, running fine. Got home and went to check on it and the coolant wasn’t hissing this time around but the coolant was bubbling in the reservoir. (Panic as in my head this always meant head gasket). Dipstick is clean - ran fine and never got above 230 at its peak - highway driving in AZ above 100 degrees out. Radiator is rusty when I take the cap off.

Dropping off to the mechanic here next week, gonna tow it there to be safe - but plan on doing a full overhaul of the cooling system. Radiator, waterpump, thermostat, hoses, etc. it’s a 98 and I believe they are all original so figured I better just get it done.

Nervous it could be a blown head gasket - but also see that air in the system can cause the bubbling in the reservoir so trying not to panic to much.

Curious what you all think.
 
Sandcrab said:
You said you had 2 hoses leaking. I guess you fixed that and added coolant. Could have a air pocket in it.
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Hoping it’s just air in the system. Just parked it here a couple hours ago after the whole scenario, and haven’t fixed the two leaking hoses just yet. Going to get it done here in the next couple of days. Was just nervous the bubbling in the reservoir tank after I got home here may be indicative of a blown head gasket. Hoping once the leaks are fixed, new coolant and burping the system will fix it. Reading some other posts it seems rad caps failing - air in the system - etc - may cause the same bubbling - so I may not be totally out of luck yet.
 
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I just purchased my TJ just recently, it had a rusty radiator I flushed 3 times changed all hoses. I took the temp sending unit in the thermostat housing while filling with water. To let the air out while filling . My was still bubbling a little in over flow,but I'm pretty sure it's the radiator cap. Mine wasn't running over 200 somtime a little lower,but when turned off would still bubbling little. We will see if cap fixes tomorrow.
 
1998WranglerTJ said:
Hoping it’s just air in the system. Just parked it here a couple hours ago after the whole scenario, and haven’t fixed the two leaking hoses just yet. Going to get it done here in the next couple of days. Was just nervous the bubbling in the reservoir tank after I got home here may be indicative of a blown head gasket. Hoping once the leaks are fixed, new coolant and burping the system will fix it. Reading some other posts it seems rad caps failing - air in the system - etc - may cause the same bubbling - so I may not be totally out of luck yet.
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Bubbling in the tank was most likely caused by the loss of pressure from the leaking hoses and possibly a weak rad cap. Lower pressure = lower boiling point.
 
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JKP said:
Bubbling in the tank was most likely caused by the loss of pressure from the leaking hoses and possibly a weak rad cap. Lower pressure = lower boiling point.
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that makes sense - kind of what I am hoping for. Was worried it might have messed with the head gasket - but it never got really hot too far out of normal so I was hopeful. Hoping once the cooling system gets all replaced it will good as new. (Doing the whole cooking system since I believe it to be all original and it is a 98 so figured it’s time)

Probably just gonna tow it to a shop and get everything done to be safe. Not sure if I wanna risk the 25 minute drive to get there
 
Sandcrab said:
I just purchased my TJ just recently, it had a rusty radiator I flushed 3 times changed all hoses. I took the temp sending unit in the thermostat housing while filling with water. To let the air out while filling . My was still bubbling a little in over flow,but I'm pretty sure it's the radiator cap. Mine wasn't running over 200 somtime a little lower,but when turned off would still bubbling little. We will see if cap fixes tomorrow.
Click to expand...

I will be curious to see if the cap fixes yours!
 
50/50 antifreeze boils at 226 at atmospheric pressure. Reduced concentration or high elevation will decrease that. This means that if your coolant temp is above what it boils at in open atmosphere, it will vaporize when the cap vents it and it will come into the bottom of the reservoir as bubbles.

As mentioned before it can also mean leak or failed cap, or head gasket but don't go chasing your tail. A suspect head gasket should be checked using a combustion gas test.
 
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Try a fresh radiator cap with the correct 18 psi pressure rating. Any air trapped in the cooling system will eventually make its way out on its own.
 
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freedom_in_4low said:
50/50 antifreeze boils at 226 at atmospheric pressure. Reduced concentration or high elevation will decrease that. This means that if your coolant temp is above what it boils at in open atmosphere, it will vaporize when the cap vents it and it will come into the bottom of the reservoir as bubbles.

As mentioned before it can also mean leak or failed cap, or head gasket but don't go chasing your tail. A suspect head gasket should be checked using a combustion gas test.
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Appreciate the insight. Will still probably do a check on the head gasket just to be sure. Still going to do a full overhaul of my cooling system too. My hopes are the leak itself and loss of pressure from the leak - plus old cooling system - was the cause.
 
Jerry Bransford said:
Try a fresh radiator cap with the correct 18 psi pressure rating. Any air trapped in the cooling system will eventually make its way out on its own.
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Thanks Jerry! I will probably just go pick up some new hoses for now and rad cap and see how it does - if anything it’ll help me get it over to the shop safely. Will test for a bad head gasket - but being that it ran fine - never got above 230 on my scanner - no coolant in oil or anything like that - thinking a cooling system overhaul should put me safely back on the road. Was taught that boiling coolant in reservoir basically meant “panic now” lol. Seems like it might now be a major issue. Staying hopeful for now
 
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Sandcrab said:
I just purchased my TJ just recently, it had a rusty radiator I flushed 3 times changed all hoses. I took the temp sending unit in the thermostat housing while filling with water. To let the air out while filling . My was still bubbling a little in over flow,but I'm pretty sure it's the radiator cap. Mine wasn't running over 200 somtime a little lower,but when turned off would still bubbling little. We will see if cap fixes tomorrow.
Click to expand...

Replaced radiator cap today no more bubbling in recovery tank. Temp running a little below 210. Thats what it looked like before flushed it.

20230602_201039.jpg
 
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My experience:

I drove my rig to the emissions station on my first drive after purchasing my rig. The cooling system boiled over 260* during the AZ emissions test while I was standing outside of the vehicle. I jumped in the rig and shut it off mid-test. I limped it out of the stall, and the coolant boiled out of the reservoir while it was parked outside the emissions test place.

I didn't blow a head gasket, so I'd like to think you will be ok. The root causes for me were due to the PO having a 210* thermostat installed that was stuck closed, bad corrosion in the system, and an electric fan that didn't turn on. (comical)

I replaced the entire coolant system with Mopar parts, and it's been solid for over three AZ summer heat (even after recently adding non-intercooled boost).

_ _

My thoughts:

In the very least, I'd replace the hoses, flush the old coolant, change the thermostat to a good known 195*, and install a new 18 psi radiator cap. You can boil the thermostat in water to ensure it opens up (isn't stuck closed).

If you do that and keep overheating at highway speeds, then I'd install a Mopar Radiator.

However, if you overheat at idle then I'd look into the fan clutch.

Might be a good time to change the water pump if you change the radiator, but it might also be fine. Your call.

Consider thermocuring your system with distilled water during the flush period if the system is really corroded. And I highly recommend draining the coolant from the block with an 8mm square socket to drain the old coolant and any rusty chunks out of the block. It's worth it.
 
Just updating here. Appreciate everyone’s advice and insight! Got an appointment up here in AZ with Jason at Absolute Offroad to put in a new thermostat, radiator, waterpump and hoses. Doing the complete overhaul.

Ordered a compression test kit and classic amazon fashion it didn’t work for the Jeep. So I will have him do a check on it just to make sure all is well.

Tell you what though, filled the radiator back up with distilled water and it poured coolant everywhere. From what I can see, it looks like a lot of coolant is leaking from the top hose plus thermostat housing, and I am guessing all the coolant dripping as far back as the rear transmission seems to be spraying back from a leaking waterpump?

Seems so strange that coolant could be leaking like that from all the way near the transmission area, but looking at other forums it seems to sometimes get back there from the fan spraying the coolant from a leaky water pump. Curious what you all think. I’ll update once everything is replaced as well.


IMG_4597.jpeg
 
1998WranglerTJ said:
Tell you what though, filled the radiator back up with distilled water and it poured coolant everywhere. From what I can see, it looks like a lot of coolant is leaking from the top hose plus thermostat housing, and I am guessing all the coolant dripping as far back as the rear transmission seems to be spraying back from a leaking waterpump?
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IMG_4600.jpg


IMG_4598.jpg



Here is another look of the puddle coming down from the rear by the transmission
 
Just to update - had the Jeep at Absolute Offroad here in PHX and had a new waterpump, thermostat, radiator, and all new hoses installed. Also did a chemical flush of the just to get all the crud out.

Drove home on the highway in 4th gear, AC cranked to max and it didn’t move past 210 the whole way home. (25 minutes on highway). Not a drop leaked. Problem seems to be solved.

Mentioned that my waterpump was toast - dry hoses, and lots of crud in the system. So the overhaul seems to have solved it all. Drives great. 👍🏼

IMG_4687.jpeg
 
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