Overheating
 

Hello everyone! I've been recently been having a problem with my standard 1992 Mazda 323. It's been overheating a bunch and I don't know what's causing it. Maybe you all can give me a hand! Here's what's going on:

When I start it cold, the idle sticks to around 1-1.5 RPMs and the heat goes skyward. This is when I just drive it around for a few minutes. Then if I turn it off and turn it back on a few seconds later or a minute later, the idle drops to around .5-.75. At this point, the heat goes to a more normal area and when I shift from second to third and third to fourth, the heat goes up close to the overheat line and drops back to a normal level. Like a yo-yo. If I'm driving in 4th, it will go up and down between these high to normal levels. The fan is working fine too btw.

Any ideas what could be the problem?

Update
 

Ok, here's an update on the car. When last I posted, the fan was working when I was looking at it. Today, I turned the car on and the fan was not moving at all. Though driving it a bit, turning the car off and on, started the fan.. I'm thinking electrical problem now. Can anyone confirm this? Maybe it's the fan? The idle was hitting 2 on the RPM meter too.

You can test the fan by disconnecting a lead from the water switch. With the lead off the fan should be turning all the time. In normal operation the fan will only turn on when the coolant reaches a certain temperature. When you turn the car on from cold the fan normally won't be turning.

If the car is moving at highway or even street speed it doesn't matter if the fan works or not, the car will remain cool. If the car is overheating at highway speed suspect thermostat stuck closed or water pump failure. Of course you shoud check that belts are good and fluid levels are correct.

The car will not necessarily remain cool at highway or street speeds. Really, that depends on the cause of overheating. If overheating at street speeds, but not at highway speeds, you could be dealing with blockage in the radiator. Not solving that will eventually lead to overheating anywhere.
Based on your description, I'd say thermostat may be sticking. Low coolant level can cause the same erratic temp. If level drops below temp sending unit, it will read hot.. Thermostat: critical, though cheap. You can pay extra for a fail-safe thermostat, which shouldn't stick closed like yours could be doing.
I'd suggest replacing thermostat and flushing radiator

2nd update
 

After some talks with a mechanic friend, he supposed that the problem was that the radiator was out of fluid. So we poured water in the rad and it worked. The next day, the problems started again and this time it was worse. The heat wasn't dropping like it did when I was hitting 4th gear. It was just constantly hot. So we surmised that the problem was a hole in the rad. So we got some rad leak sealer, put that in, poured water up to the appropriate levels and it worked like a charm! Thanks for all the help everyone! Hope this helps someone else!