Okay my daily driver is an Automatic 2000 Honda Civic LX. The overheating problem is quite weird. After letting it warm up, the temp. gauge would rise quite rapidly..like within 2 seconds, but it would ONLY rise when I am at a stop light or below 2.5k RPMS. What I do to counter this problem is I would put the car in neutral and rev it above 2.5k and the needle would drop...of course quite rapidly. It's weird because how can the temp. rise and fall like that so fast?

Here are the things that I have done:
-Flushed the coolant, refilled it, started the car with the radiator cap off until the fan comes on 3x times, re-top if off, and replaced the cap.
-I bought an AUTOMATIC radiator from Ebay. I did notice that it's a single core radiator with 2 extra outlets for the automatic transmission cooling lines. Maybe I need a dual-core radiator considering that I have an automatic?
-The fan DOES come on but the cooling isn't sufficient enough and the car still overheats.

 

Sounds like a bad water pump.

 

Check the thermostat. I had issues overheating and that was my culprit. If so, they're cheap and not difficult to replace.

 

Some places will check it out for free. Just tell them the issue and make sure you mention you want to know the problem before they fix it. Once they tell you, tell them you're going to wait it out, hold off til payday, whatever, just take the info and do it yourself - if you're capable of course.

 

I hoping it's not the water pump but to check the thermostat, can I just ride around with no thermostat? If I still get the same overheating problem then I can rule out the thermostat. Also, the car doesn't seem to overheat during late afternoons/night due to the cold weather..just during mid days when it's scorching hot outside.

 

Did you properly bleed the system?
Air in the system would result in rapid changes in temp. gauge readings. 94