Boiling coolant after long trips

[Baumer]

I have a 2001 Toyota 4runner sport, and lately I have noticed that the coolant will be boiling in the resivoir after long trips where the engine is put under a lot of stress (4-5 hours and usually when driving uphill into the mountains. The same trip back down the hill will not cause this problem). There isn't any visible leaks in the radiator or hoses, and the fan is working. The vehicle runs perfectly outside of this problem.

I am trying to diagnose what the potential problem could be. I am thinking possibly a very small leak I am not seeing, thermostat, or maybe even incorrect coolant to water ratio (right now I am using a 50/50 mix). Is there anything else it could potentially be?

Paul

 

[Drew1122]

I had a Camry that did a similiar thing. It was fine for the first hour or so of driving but if you drove it any longer it would start to boil in the overflow tank. After changing the thermostat and fresh coolant it kept doing it so we changed the water pump and the problem went away. I guess the bearing in the pump would get hot after awhile and not pump enough coolant throught the engine fast enough to keep it cool. Good luck....

 

[delz05]

Classic symptom of a bad water pump... get it replaced before a cylinder head or gasket blows.