Cooling System Question

I have a 2008 Tacoma, 4-cyl., manual that I've driven for about 5,000 miles. It overheated this morning (~90 deg F outside). After it cooled, a friend topped off the radiator with distilled water while it idled, and put the cap on. It took nearly 2-quarts of distilled water to top off. I drove it home about 5-miles, and no problem. No overheating, not leaks observed. It came with yellow colored coolant, but the manuals all say Toyota-Red. The auxiliary tank behind the radiator was always right at the fill line, but the radiator was about 2-quarts low. (1.) What was the overheating problem? (2.) What should I do??

 

It could be a lot of things:

Sticking thermostat.
Defective worn water pump.
Clogged radiator.
Defective fan clutch.

http://affordableautohopkins.com/common-reasons-your-car-overheats/

https://worldclassautoservice.com/common-causes-of-overheating-and-what-to-do-about-it/

 

At this point it don't matter what color the coolant is. The question is where did those 2 quarts go?

From JimmyH's choices, only a leaking water pump can explain the loss of coolant. Check the weep hole for leakage; a small leak may evaporate before hitting the ground, thus you may not see any coolant on the ground/floor until the leak becomes worse. Other disappearing coolant can be explained by a bad radiator cap; other leaking areas (heater or radiator hoses, heater core, or radiator itself); bad head gasket; or internal radiator leak (with ATF reservor - see strawberry milkshake effect).

 

As I said there could be a lot of causes... He could also have a leaking head gasket...

 

I covered that.