1990 Camry Overheating

In her old age, my beloved 1990 Toyota Camry, has begun to experience hot flashes! A few nights ago, I noticed just minutes after starting her up that her temperature began to rise. It dropped back down and I proceeded to drive. After about 10 minutes, the temperature gauge was all the way into the red. Her coolant levels were fine and the fan was working. Tried again a few days later and once again, after driving about 5 minutes her temperature began to rise. On both occasions I turned the heat on, but only cold air blew out.

I checked the rediator hoses, and the top hose was hot, while the bottom was only slightly warm. This seems to indicate to me that I may have a problem with the thermostat, but I'm not sure where the heat not working comes into play.

Any suggestions/thoughts? Also, is changing the thermostat in that make/model a difficult task?

but

Your investigation was good and you have drawn a good conclusion. From what you have noted, virtually all circulation has ceased, and considering this is a sudden onset thing, the t/stat is the prime suspect.

Its possible the bottom hose is collapsing (suction occurs in the bottom hose, which is why they often use a spring inside it), but you should see that when you were checking the temp differential.

There is one anomaly tho,...if circulation is blocked and the bottom tank is cool,..the cooling fan (not the ACAfan) should not have come on,...unless the heat in the upper part of the rad finally seeped down??

I have seen an '84 Volvo 4 cyl once, which had its water-pump impeller spin on its shaft,...but thats comparitively rare.

If its the 4 cyl,.the t/stat is part of the water-pump housing and is easily accessed from the front from memory.

Jason