In my 1991 4Runner 22RE engine: I have the stated problem and the search of the solution procedure to start where the rule indicates ...... rectify the seat of the cylinder head, install the new gasket, check clucht fan .. . perfect, new water pump, new thermostat, radiator checked, hose, in perfect condition, no leaks, new radiator cap and ignition timing according to the manual ....... but when you shut the car, listening instant boiling coolant and pass into the reservoir.
In my review of various forum, I was referred to make the so-called t-block test: start the engine and the 30 seconds press the upper hose (which runs from the thermostat to the radiator) and whether notes tense is an indication that there is a leak in the cylinder head to the cooling circuit.... in my case that hose under the pressure test do not observed this situation.
The temperature gauge indicates NORMAL OPERATING! and being seen on the engine, ALL related accessories and the cooling cycle are working according to the rule but something is wrong!.
I would like to thank any suggestions before proceeding to disassemble again to start the revision of the cylinder block or head for example to find internal cracks ........................ THANKS IN ADVANCE.

 

Sound like you rad cap isn't holding pressure on the system. When motor is running water is getting cooled and circulated but when you cut it off the fan stops so the cooling stops, and when know pressure is built up it lets the water boil.

 

Water (coolant) under pressure has a higher boiling point. As finneys98xj said above, your radiator cap needs replacing or you have a leak.

 

My '89 dos the same thing

 

Radiator cap is bad, or you have a good amount of air in the cooling system.