Help with cooling system – Radiator hose blowing off, pressure test and block test passing

[orange57]

Needing Help

2018 GX460 4.6L V8, 101.7K miles.

Replaced the radiator a couple of weeks back. New radiator w/cap, hoses, thermostat w/housing, coolant. All procured from Bell Lexus, picked up in person.

Finished on a Sunday, drove the truck around in the AZ 115°F heat, no issues.

The day after, my wife was driving the car and the lower radiator hose blew off the radiator. Had to get the car towed home.

I got things reset, re-bled the system all seemed good. Let the car sit till the weekend, as I didn’t have time for it.

Took it on a short drive, and the hose blew off again after ~3 miles.

Just today, 23 August 2026, I pulled the lower hose, and installed the one I removed. The new one looks like it is bulging a bit.

I did a radiator pressure test, held pressure for 10 minutes, no issue.

I bought a block test kit. Got the system filled, mostly distilled water, let it warm up to operating temp, running the engine at ~2K rpm to get it warmed up. Block test not showing a blown head gasket.

When I push the gas, and rev it there is some geysering in the fill funnel. This seems not normal to me. I have a video, but wont' let me attach it.

Thoughts on next steps?

 

[Biginboca]

I recently bled my cooling system because I had done a coolant change using the block drains. I had a little geysering in the funnel also during the bleed when I rev’ed the engine. It took almost 20 mins for the bleed to be successful with no more bubbles after rev’ing the engine. Make sure your upper radiator hose feels hot, not warm, for a while before you stop the bleed. Want to make sure the thermostat is open for a while and hold the engine like you said at around 2k-2.5k rpms for a few minutes after the upper hose is hot.

 

[BC11SVT]

I keep hearing of these incidents and wonder are you guys replacing the hose clamps and are you making sure the interior or the radiator hose and the radiator are free of coolant residue before sliding the hoses on?
Using rubbing alcohol on the interior of the radiator hoses as the "lubricant" when you push the hose on will usually will produce of nice mechanical bond once it evaporates.

 

[r2m]

Needing Help

2018 GX460 4.6L V8, 101.7K miles.

Replaced the radiator a couple of weeks back. New radiator w/cap, hoses, thermostat w/housing, coolant. All procured from Bell Lexus, picked up in person.

Finished on a Sunday, drove the truck around in the AZ 115°F heat, no issues.

The day after, my wife was driving the car and the lower radiator hose blew off the radiator. Had to get the car towed home.

I got things reset, re-bled the system all seemed good. Let the car sit till the weekend, as I didn’t have time for it.

Took it on a short drive, and the hose blew off again after ~3 miles.

Just today, 23 August 2026, I pulled the lower hose, and installed the one I removed. The new one looks like it is bulging a bit.

I did a radiator pressure test, held pressure for 10 minutes, no issue.

I bought a block test kit. Got the system filled, mostly distilled water, let it warm up to operating temp, running the engine at ~2K rpm to get it warmed up. Block test not showing a blown head gasket.

When I push the gas, and rev it there is some geysering in the fill funnel. This seems not normal to me. I have a video, but wont' let me attach it.

Thoughts on next steps?

First, Woody doesn't allow video clips to be uploaded. You have to do a Youtube and post the link.
Now, regarding you being "hosed" (sorry for the pun). Another fellow on here is having the same issue.
May I ask the following:

1. Is the bottom hose completely and thoroughly pushed on at both ends: up and over the "bumps/barbed" fittings on the engine and radiator?
2. Are you using wide enough/strong enough hose clamps?
3. Are you tightening those hose clamps "gorilla" tight using a socket rather than a flat head screwdriver to tighten the hose clamps?
4. Is the hose OEM or a Chinese knock-off?

Hope this helps.

 

[Rednexus]

A few thoughts:

1. What pressure did you run the pressure test at? Looks like the GX460 radiator cap is rated at 16 psi. I'd personally run the test longer (say 30 minutes) and try a slightly higher PSI (maybe 20-22 psi) and watch the lower hose like a hawk for signs of leakage if you are getting bleed-down. If you aren't getting any leakage at the lower hose with a extended pressure test above the OEM rated cap pressure, that also would indicate the system is somehow getting over-pressurized above that and the pressure is not venting off via the radiator cap.

2. How are you refilling it? I'm not a fan of the burping funnels. I'd suggest a vacuum filler (about $90 at Harbor Freight), and make sure that the heater was on at full-blast when you shut the rig off for the refill. This is much quicker, more reliable, and much less messy than refilling and burping a running engine.

3. If the "block test" is testing for combustion gasses in the coolant, it may give you a false negative with a fresh radiator fill. If the head gasket is only slightly blown it may take some driving miles to get enough combustion gasses in the coolant to show up in the test.