In June my wife and I took a road/camping trip to the Sawtooth mountains in Southern Idaho. We live in Eastern Washington so we have lots of mountain passes and windy mountain roads. We were into out trip a few days when the heat hit the Northwest. Day time temps reaching over 100 degrees. My vaca rig is my 06 Gx470 with 175k on the clock. It has a 2.5 inch OME lift and I tow a 18 foot single axle camp trailer with flipped axle lift. We prefer out of the way lakes and camp sites. We needed to make our way into Southern Idaho and through Oregon to pickup a new puppy. So we had some days to kill on the road. A week in we made our way through Twin Falls and were headed South to City of the Rocks National Park. This area is super dry and there is nothing around. As we were pulling our last big steep grade, just as I started to crest the top my engine temp pegged. I killed the engine while in motion and we coasted over the crest and found a wide spot to pull over. I lifted the hood and the antifreeze was boiling out of the burp tank. So I thought it was an internal issue. I have performed all maintenance on this rig and it has seen 2 timing belts, water pump and radiator replacement. I waited till the boiling slowed and I restarted the engine. I noticed the auxilary fan wasnt running. I cut the wire to some auxilary lights and wired the auxilary fan in. I had a little antifreeze with me and water from the rv holding tank so I started getting fluids back into the rig. I was still convinced something inside the engine had let go. After a while it was cool enough to pop the radiator cap. And there it was,,,, the center shaft on the cap had broke and the spring was setting in the radiator. With the fan hard wired we were able to limp back to twin falls at 55 mph on the back roads. I stopped at Napa and picked up a radiator cap and the fan started working normally. The next morning I took it to the Toyota dealer and had them flush the system and check it out and they said it was good to go. We ended up driving home in temps up to 115 degrees towing our trailer through Oregon and back through Washington..
My radiator cap was still the factory one after all these years and all the maintenance it was never changed. Oh and I now carry a spare cap also.
The auxilary fan runs on pressure. Normally high temp builds high pressure but in this case the cap was not able to keep the pressure in so the fan switch didnt know the system was overheating.

 

Thanks for sharing this story. A good radiator cap is important!

 

Thanks! I am planning on a road trip as well, just got a OEM radiator cap (replaced the current and kept one as spare). Great call