Car's running beautifully until on returning from trip to the store and back, 12 miles, get home via our hill, pull up and vmmmph, cloud of steam courtesy of a popped top hose detached from header tank. Not a big noise just vmmmph.

Any clues as to why this happened ?

Loose clamp? Temp spike causing 'weak' point to 'give'? (what would cause the spike?)

I'd decide if new hoses are in order while inspecting clamps, radiator, external tank and cap, decide if any need replacing and go from there.

Luck and enjoy the Runner.

Happened to me too and cost me an engine. Like said; clamps might be weak. Could be the radiator got hot and built up enough pressure to blow the hose. How old is the radiator?

I wondered if a sticky thermostat caused it. I'll probably never know but I hope you find out why.

Oh, on mine I did install a new radiator cap, so it's possible it didn't release pressure into the overflow tank thereby causing enough pressure to blow the hose off. On mine this is likely what happened but I'll never know for sure at this point.

Radiator cap. Controls/releases pressure in radiator. Other possibility is sudden and catastrophic head gasket failure.

Possibly coolant way low, and lots of pressure from making steam.

Better a hose to go then an end tank like in my Cherokee. Had a head gasket leak that contributed


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^^^ Coolant low ^^^
This happened more than once on my 7.4 '95 Chevy pickup. Previous owner replaced the radiator with aftermarket aluminum unit that had poor rad. cap fitment. Over time, the rad. cap would leak coolant and eventually the steam pressure would blow the upper hose off - then the fan would eat the hose.
After the 2nd time, I fixed it with a piece of bicycle inner tube cut with scissors to double up the seal on the rad. cap. Has not leaked or blown a hose in 2 years.

Which is why I won't ever truly know what happened because the overheating caused serious warping of the heads.

The egg or the chicken; which was first? Did the cap or something else cause the hose to blow or did the head gasket(s) blow and cause the overheating? It's possible the new cap worked correctly but also put a higher pressure into the cooling system causing an already weak gasket to blow. The old cap was quite tired with a weak spring which is why I replaced it. Better the engine blew close to home than on a road trip though.

In my case it's a moot point. Water under the bridge. I do wish I could have learned something from the experience other than how to tear down the top end of a 3.4L T4R engine.

It does reinforce my belief in being proactive with maintenance as much as possible though so I guess that's something. I think it's better to fix something that's not broken (yet) than wait for it to leave me stranded because I was too cheap or lazy to do basic maintenance.

I do think the alarm on the Ultragauge for coolant temps is worth triple its weight in gold. Two out of my 3 cars now have them. The 3rd will soon. The Ford F150 I had overheated once but it had a safety feature that put it into a "limp mode" which prevents catastrophic damage. I wish our Toyota's had something similar.

Live and learn I suppose...

^^^ This is the #1 reason to have an Ultragauge - no one can monitor their temp gauge full time, the UG's alarm is a godsend for these situations.

I also suspect low coolant. Fluid alone won't expand enough to blow a hose until your gauge is in the red. If coolant was low and there's sections of the head that were exposed to air cooling and not fluid, it would cause the heads to overheat (air is poor at heat transfer compared to fluids) and once the coolant were to contact the overheated metal, coolant boils off rapidly and expands. Hose blows off.

Thanks for all the observations on my dilemma.
Today, from NAPA, I got two new hoses, (they didn't have proper clips) a new thermostat and a radiator cap and went to work.
Naturally, there were hazards on the way. I relieved the belt tension to discover the tensioning bolt and its associated nut/bolt item were not working, so I fixed that. Then, I think a PO had been attempting to change thermostat without moving betl and he mashed up the lower inside nut of the three that hold the housing on. That took some determination but I won with nothing untoward happening. All the parts went together as expected.
Then I looked at the new radiator cap against the old one and noticed the old one had resistance on the spring reliever to the over flow tank.
Could that be it ? I had an over flow snag 6 months ago and thought it's time to change out timing belt, pump etc. Not wanting to play that hard, I took it to a local goodman who discovered the little black divot in the middle of the cap had gone. He said replace that and see what happens and he was spot on.
So this is a replacement from NAPA that clapped out and gave me much heart ache. Gonna get an OEM cap for sure. Don't want this problem again.
Thanks for all your help and guidance chaps.

My 02 did the same thing the first day I bought it that was 2 years ago with 140,000 miles I was actually on the way to the DMV to register it and the moment i pulled in the lot I saw the steam and heard the pop the top hose had popped off after looking Into it I just got a new OEM radiator cap and refilled it I never let the engine overheat I turned it off immediately and today I just rolled over on 170,000 miles and I’ve never had another issue with it so I think it must have just been the bad radiator cap.

I also sprayed a dot of red spray paint where the hose meets the radiator and checked it after the first 5-6 trips to see if it was sliding off but it never moved again I’m certain it was the bad cap. It scared the crap out there of me initially but like I said 2 years and 30,000 miles later it’s never given me any other trouble so it must have just been the cap.