Subject: Over Heating
Question: 1994 1.8L Eclipse. I have replace the water pump, thermostate and radiator. When driving for a while, the temperature creeps up near the redline and shoots back down to the normal temperature. The radiator fans are working. I'm guessing it has something to do with the electrical parts. Why, when the temperature rises near the redline (this last about 20-30 seconds), I notice the dashboard lights get very bright and when the temperature falls the lights go back to normal. What other parts would you recommend changing? And a relay I noticed, could you please tell me what it is/does, the radiator vent relay.
Thank you. David
Answer: David,
I've never heard of a "radiator vent relay". The only relay I know of that directly associated with the radiator is the Radiator Fan Motor Relay.

This is my best guess as to what causing your problem. Your problem could be due to a worn water pump pulley.

Your crankshaft pulley drives a belt that is connected to your water pump pulley and your alternator pulley. If your water pump pulley is not enaging (turning) your water pump, your temperature will skyrocket to the redline. Also, if the water pump is not engaging, more of your engine's power will be focused on turning your alternator. With more engine power turning your alternator, more voltage/current will be produced than normal; hence, your dashboard lights can get brighter.

But when your water pump finally engages, your temperature will drop quickly, and less power will be supplied to your alternator so your dashboard lights will return to normal brightness.

If your sure your pulley/pump is not the problem, your problem may be electrical related. Your car's computer may be malfunctioning. Read this article for further information:
http://90gsx.com/eclipse/cap/caps.htm

If your ECU is malfuncting, you will start to get all sorts of strange and random problems. But re-check your thermostat and all belts connections before pulling your ECU.
Good luck!