Coolant system question! (Blown upper radiator hose)

Was driving home from an hour away, and just as I got into my neighborhood (thank god) my upper radiator hose blew a few inch hole in it.

I have a hard time believing that it could build enough pressure to blow a hole in it like that without anything else being the cause for catastrophic pressure???

Engine was not overheated (at least the gauge was right at temp)

So I have a few questions and would appreciate help very much!

Would a broken thermostat cause the upper radiator hose to blow?

Is there normally a good amount of pressure in both the upper and lower hoses?

Does the lower radiator hose stay luke-warm to the touch?

Could a bad temp gauge / thermometer still show the car heating up to running temp, and stay there?

What part of that system is the temperature gauge pulling temp from? Could it be overheating without the temperature gauge getting the hot fluid to it???

How do you know if a water pump is bad? I pulled the belt off and the water pump spins freely back and forth, doesn't seem to make lots of noise etc... I replaced mine five years ago-ish.

So far today, I did a radiator flush, heater core flush, replaced the upper hose, and replaced the radiator cap (that is on the reservoir/overflow tank)

When I started jeep up, it got to running temp and stayed there, cooked off all the water that i got on the engine and then was fine, but the fan never kicked on when it got to running temp (the temp never raised passed running temp either, somehow) but after a bit I noticed some steam coming off the radiator... It did get water all over it from doing the flush, so maybe it took longer for the radiator to get hot enough to evaporate it off than the rest of the engine???
Both hoses seemed to have a good amount of pressure in them.. Bottom one stayed luke-warm, the top one got really warm... Not too hot to touch but it was hot enough....

Thanks in advance guys. I think I will replace thermostat and lower hose to be safe... Any ideas if it could be radiator or water pump?

Which engine do you have?

Hoses and belts go bad. Very good it wasn't overheated! Pressure in cooling systems is only 12-14psi. Thermostats fail open or closed. Closed fails can raise the temps and a bad, or wrong, radiator cap can cause problems. Water pumps wear out too, usually the bearing seal which affects the system's ability to hold pressure and washes the grease out of the bearing.

The reservoir cap in 3.7 engine is 16 psi. Is it possible that the top rad hose alone was older ready to blow? Use Mopar preferably, or EPDM spec'd hoses only.
Is your system with flush now completely just tap water? Hoat or Zerex G-05 only to be used.
Thermostat Mopar ONLY. It fits correctly and has the seal built in. It is spec'd to open at 195F.
The lower rad hose does stay cooler than the top rad hose. The top rad hose if weak can burst and it's tight/under pressure, once hot.
With EPDM hoses, it is best not to squeeze them, as in an older hose,scales if any, can then be freed by the squeezing motion.

If you squeeze your upper hose all the time(ha ha) is there still a danger? I usually do it everytime I open my hood to see if fluid is moving around.

BAD Idea.
Also hot & squeezing can initiate cracks and then when you least expect it....

Carry a spare Upper hose for the unexpected, is a GOOD idea!!

LibertyTC said:

BAD Idea.
Also hot & squeezing can initiate cracks and then when you least expect it....

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Carry a spare Upper hose for the unexpected, is a GOOD idea!!

Click to expand...

I actually DO have both the upper and lower old hoses, just in case, as they were replaced with my Rad, but were still in pretty good shape.

Fair spares!

Okay so, I replaced the thermostat too, and now the upper gets hot and lower stays cool, but neither have much pressure at all.

It gets up to temp and stays there, but the fan never kicks on... I am confused as how the fan is not kicking on to cool down the coolant in the radiator when I am not moving, but the temperature is staying right in the middle...

Could the temperature sensor show normal temp if the water pump wasn't circulating the fluid? Or would the fluid at the sensor be the first to overheat?

I take it the T-stat was installed in the correct orientation?

there's a few parameters that the fan takes into consideration before kicking on.

OPERATION
The electric radiator cooling fan is controlled by the Powertrain Control Module (PCM) through the radiator cooling fan relay. The PCM regulates fan operation based on input from the engine coolant temperature sensor, battery temperature sensor,air
conditioning select switch and vehicle speed. The fan is not energized during engine cranking regardless of the electrical input from the temperature sensors and ,air conditioning switch. However, if engine operation conditions warrant fan engagement, the fan will run once engine starts.

Vehicles Equipped with AC:
In addition to using coolant temperature and battery temperature sensor to control cooling fan operation, the cooling fan will also be engaged when the ,air conditioning system is activated. The relay is also energized when, air conditioning is selected and coolant temperature is above 95° C ( 203° F), or , air conditioning is selected and battery temperature sensor is above 41° C (106°F). It will then de-energize when , air conditioning is selected and coolant temperature is below 92° C (198° F), or , air conditioning is selected and battery temperature is below 38° C (100° F).


*the other thing to consider is your e-rad fan relay.
the early model KJ had a beefier relay to replace the factory relay.

You really should include what year your KJ is.

uss2defiant said:

I take it the T-stat was installed in the correct orientation?

there's a few parameters that the fan takes into consideration before kicking on.

OPERATION
The electric radiator cooling fan is controlled by the Powertrain Control Module (PCM) through the radiator cooling fan relay. The PCM regulates fan operation based on input from the engine coolant temperature sensor, battery temperature sensor,air
conditioning select switch and vehicle speed. The fan is not energized during engine cranking regardless of the electrical input from the temperature sensors and ,air conditioning switch. However, if engine operation conditions warrant fan engagement, the fan will run once engine starts.

Vehicles Equipped with AC:
In addition to using coolant temperature and battery temperature sensor to control cooling fan operation, the cooling fan will also be engaged when the ,air conditioning system is activated. The relay is also energized when, air conditioning is selected and coolant temperature is above 95° C ( 203° F), or , air conditioning is selected and battery temperature sensor is above 41° C (106°F). It will then de-energize when , air conditioning is selected and coolant temperature is below 92° C (198° F), or , air conditioning is selected and battery temperature is below 38° C (100° F).


*the other thing to consider is your e-rad fan relay.
the early model KJ had a beefier relay to replace the factory relay.

You really should include what year your KJ is.

Click to expand...

Thank you very much for all the info. I appreciate it.
Do you know if the temperature could raise up to normal running temp, and then stay there, if the water pump wasn't flowing the coolant? Or is the coolant where the temperature sensor is, the first to get over heated?

The temp gauge is not accurate so if you wanted accurate coolant temperature, I would use an obd2 reader.

If the water pump and/or t-stat isn't working properly then the engine will certainly overheat.

Okay, so let's say the new thermostat I put in works great, and the water pump I replaced 5 years ago is good, and everything else is fine, and it is not overheating...

Could a bad or clogged radiator be the cause? Is a clogged radiator basically the only way the radiator goes bad? I thought there might be residual fluid on the radiator that was burning off after the jeep got up to temp, but it sat all day and I just took it for a drive and again:

Temperature rose up to running temp, and stayed steady there.
The fan never turned on (But it does work, and kicks on if I turn the AC on)
When I parked, there was more steam coming from radiator, and both radiator hoses were pretty firm. Still somewhat squeezable but a good amount of pressure...

I am trying to figure out how the temperature could stay at normal temp (at least at the sensor), not triggering the fan to kick on, but somehow there is still an issue and steam coming from radiator... I would think if the radiator was clogged, there wouldn't be enough fluid to cool it down and overheat???

I noticed some pressure coming from the reservoir and the fluid in there was warm, so maybe there was enough fluid there plus in the engine with the water pump circulating that around to keep it cool, without the radiator working??

I do understand your concerns.
Traditionally the electrical cooling fan does not turn on until the temps reach about 230 f off the top of my head.
Anytime after the jeep is warmed up and you turn on the AC the fan should also be on.
You will need an obd2 reader or scanguage to read the actual temp being reported from the pcm /temp sensor.

LibertyTC said:

I do understand your concerns.
Traditionally the electrical cooling fan does not turn on until the temps reach about 230 f off the top of my head.
Anytime after the jeep is warmed up and you turn on the AC the fan should also be on.
You will need an obd2 reader or scanguage to read the actual temp being reported from the pcm /temp sensor.

Click to expand...

I actually just got back from running it around with my odbll reader! It did kick on at 219 degrees... So, I think my fan is good, temperature sensor is good, thermostat is brand new, hose is new, reservoir cap is new...
This time I did not notice any steam coming from radiator, but I did notice that the bottom hose was just as hot as the top, and both were pretty firm...

Sounds like you are now good to go !
Did you use Hoat Coolant?

steam is probably residue radiator fluid/water from the blown hose.

I already gave you the e-rad fan parameters so just follow that.

I also like to pressure test the cooling system with a loaner tool set from a local auto part store.

LibertyTC said:

Sounds like you are now good to go !
Did you use Hoat Coolant?

Click to expand...

Yes sir!

As long as it is regular for both hoses to be hot and pretty firm with pressure while hot, then I think I might be good to go...
Thanks for all the help guys, sometimes I overthink stuff that is fine but I like to be sure I cover every little detail before I go driving far from home haha.

uss2defiant said:

steam is probably residue radiator fluid/water from the blown hose.

I already gave you the e-rad fan parameters so just follow that.

I also like to pressure test the cooling system with a loaner tool set from a local auto part store.

Click to expand...

I will look into that! I will say, for some reason the bleed valve bolt/nut is impossible to get off my jeep. I tried the big allen key, almost broke it, tried an impact with an alllen key adapter, tried a big solid metal key and hitting it with a hammer. that thing will not move (all of this after using PBlaster 3 times and letting it sit for a long time).

Just invite me over, Ill have that hex off in no time!

Forget that hex allan key, either an impact gun or a hex socket w/ a long handle ratchet should do it.
Fluid film- let that sit in overnight.

LibertyTC said:

Just invite me over, Ill have that hex off in no time!

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Forget that hex allan key, either an impact gun or a hex socket w/ a long handle ratchet should do it.
Fluid film- let that sit in overnight.

Click to expand...

Haha awesome. The hex key I used started turning / bending the inside of the bolt though... I am not sure much more force will do anything but destroy it!