Top radiator hose blew off -
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post #1 of 8 Old 06-26-2019, 03:54 PM Thread Starter
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2001 WJ 
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Top radiator hose blew off

Recently I replaced my top radiator hose because there was a hole up top. The engine has 10K on a new motor. I pulled the existing one and had it rebuilt at Jeep. Yesterday I drove to CHeyenne from Denver and back. No issues. Later that night I went to Red Rocks, stop and go traffic and steam came out of my hood. I lost a bit of liquid. The Jeep was too hot to turn over.

Later that night after the concert I drove my jeep to the gas station. I filled it up wiht three 32 ounce cups of water. I was able to get home with a low coolant light.

I'm guessing I might not have bleed the system well when I originally replaced the hose. Thougts?

Why would the hose blow off. THis Jeep never leaks normally

2001 Jeep Grand Cherokee Limited
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4.7 V8
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post #2 of 8 Old 06-26-2019, 04:13 PM
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So the hose actually blew off from the engine or radiator?

Or are you using the term 'blew off' to describe the overflow tank boiling over?

If the former, then it's likely due to the length of the upper radiator hose. Many folks, myself included, erroneously cut the upper radiator hose on the 4.7 too short. Many aftermarket hoses appear to be too long when first installed and end up getting cut shorter. The problem is this won't allow the hose to flex enough to account for engine movement under heavy acceleration. This can cause the hose to leak under load or pull off the radiator or engine entirely.

If you're referring to the latter, then it's entirely possible the cooling system wasn't bled completely when you replaced the hose and there was an air pocket that was causing the boiling over out of the overflow tank. The FSM recommends 3 full complete heating and cooling cycles to properly bleed the system of air on the 4.7. The means running the engine until the thermostat opens and then letting it cool completely 3 times.

His: '00 WJ 4.7 Limited- Some stuff

Hers: '03 WJ 4.7 Laredo- Some more stuff

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post #3 of 8 Old 06-26-2019, 05:01 PM
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Almost the exact same scenario for me. 3k after a new engine install and a new upper rad hose, and I was pulling up my (very steep) driveway and when I got to the top had steam coming out the hood. I guess I may have drove up the driveway a little faster than normal and the extra pressure blew the hose off the radiator side. Temp got up to 235-240deg but doesn't seem to have affected anything.

I just went to autozone, picked up a couple gallons of coolant, a worm drive hose clamp, and a new radiator cap. Then just topped off the fluid at the radiator cap, ran the engine to get the bubbles out and kept adding till it was full.

I think the old hose clamp was just too weak and allowed the hose to blow off. Also I was worried my rad cap wasn't working properly as it should have released some of the pressure so I decided to replace that too. It's been fine since but it hasn't completely restored my confidence.
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post #4 of 8 Old 10-14-2019, 01:16 AM
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I had this same thing happen to me. Itís been twice now. The first time it happened, my engine overheated and I ended up dropping a valve seat and hacking my head. I replace the engine and after 800 miles it happened again. I was able to shut it down immediately and let it cool off and get to some eater. It took a little over two gallons to get it full. Iím amazed that two gallons was able to spew out the upper radioator hose. It blew off at the radiator. When I put the new motor in, I replaced the thermostat, hoses and cap. I am using the original clamp and now the previous post has me thinking that perhaps my clamp is weak. Iím a at a loss as to what could be causing my hose to pop off. I was driving up steep off camber trails both times that it happened. New motor mounts so my engine isnít moving that much, I believe itís pressure related. Any suggestions would be much appreciated. Would a bad water pump, radiator or heater core cause an upper radiator hose to come off? Time to go to the dealer and spend $40 on two gallons of the Mopar orange coolant. Since I was only able to add tap water, Iíll drain and refill with 50/59 coolant and distilled water tomorrow.

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post #5 of 8 Old 10-14-2019, 01:42 AM
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The radiator hoses can pop off for several reasons. Typically it is because the hose or the plastic neck that connects it to the radiator/component has failed. You will want to inspect both sides of the problem hose, and determine if the clamp is doing its job.
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post #6 of 8 Old 10-14-2019, 01:36 PM
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Make sure your engine isn't torque-moving excessively under throttle due to, for instance, a weak or failed engine mount.

On the WJ 4.7, the coolant inlet on the timing cover and the upper radiator port are oriented to one another in a way that basically demands a very narrow range of hose length. Too short and you get accelerated wear fatigue to the plastic radiator at certain points. Too long and the hose has a tendency to bulge - usually on the engine side.

The engineers apparently tried to ameliorate the short hose problem by angling the timing cover outlet rather than pointing it directly at the radiator. That would have the effect of allowing a somewhat longer hose because, in general, longer hoses can accommodate more flex and slack.

Anyway, I've posted extensively here in the past about wear fatigue issues with the upper hose neck/inlet area on the radiator that I believe occur under normal circumstances. Even with the angled outlet and formed hose, it seems it's simply still too short to accommodate the necessary give and take from normal engine movement. Maybe some kind of accordion style hose would help, but otherwise, the plastic composite portion of the radiator seems to not be robust enough to take the flex fatigue long term.

If you do end up developing a small fracture near that area on the radiator (usually hidden under the fan shroud) it will become a vapor leak that robs the system of coolant AND more ominously, prevents proper replenishment from the overflow reservoir, which is a normal function that relies on the vacuum of a sealed system to work properly. That is, a hole or leak, especially at the top of the system, will allow the natural cool down vacuum to suck air into the system rather than coolant from the tank.

Ultimately, you will begin to have overheat issues while all the while you think the system has plenty of coolant because the overflow tank remains full.

What's worse is that once you actually begin to notice overheating symptoms like the coolant gauge reading high, the potential for damage will have already occured because a circulating air pocket in the system has the potential to introduce selective overheating in the heads through the inefficiency of cavitated/bubbly coolant.

The 4.7 heads do not like to be overheated, even a little bit. While apparently they don't actually crack so easily, they can warp easily - just enough to compromise a head gasket, which will usually manifest itself in an engine that runs OK but consumes coolant internally. The overheated heads may also drop a valve seat.

Rage! Rage against the dying of the Jeep.

99 WJ Limited 4.7/NP242
01 WJ Laredo 4.7/NP242
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post #7 of 8 Old 10-17-2019, 01:07 PM
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Can someone describe the direction of coolant flow? Iím going to attempt a cooling system flush and am thinking to remove the thermostat, drain as much as I can and then use a hose to introduce fresh water at the Ďstartí of the system and then a bucket to catch all the old fluid at the Ďendí of the system.

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post #8 of 8 Old 10-17-2019, 11:28 PM
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Below is some info from on coolant service, flushing, coolant flow, etc. Towards the end is a diagram of the coolant flow of the 4.0 system but I don't see the same for the 4.7 system.

I followed the below write-up by Chris Hager on flushing my 04 4.7 cooling system and it worked real well.

I used 6-8 gals of distilled water for flushing 3-4 times, didn't remove the thermostat but let it heat up to temp where it opened each time, and added 2 gals of straight Mopar HOAT antifreeze at the end while was able to squeeze it in. I didn't use the radiator petcock and just removed the bottom radiator hose for draining between cool-downs.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)

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