Hi steph53-ga:
Based on my personal experience bailing friends out of similar
situations, I can guarantee you that this problem is not exclusively
the domain of the blonde-haired part of the population... and, while
it seems strange to someone like myself who spent many days of my
youth under the hood of many cars, most people I know don't even know
how to pop open the hood of their own car!
The problem you describe matches the classic symptoms of a failed or
failing thermostat in your engine's cooling system. The thermostat in
a 93 Honda Civic Si is a mechanical, temperature-controlled device
that opens up as the coolant temperature around it rises, to allow
greater flow of coolant to the radiator (for cooling down the
coolant).
The cabin heater in your car is also fed through the cooling system,
independent of the thermostat. When the thermostat has failed, the
only way to extract sizable amounts of heat from the coolant
circulating in the engine is through the heater. If you turn off the
heater, the heat has nowhere to go, so naturally the temperature will
rise.
This is a potentially dangerous situation, one that needs to be
repaired as soon as possible. If the engine continues to run at
higher-than-normal temperatures, even during these winter months, you
run the risk of permanent, serious (ie. expensive) damage to the
engine block, the water pump, the pistons, and even your cabin heating
system.
Replacing a thermostat is not that hard, but is best done by a
mechanic if you are not intimately familiar with working on your car's
engine. Make sure you run your cabin heater at full blast and max
temperature on your way to the garage!
For corroboration of what I am telling you, check out the following
message thread for a very similar problem:
Overheating Honda - Heater will cool down
http://www.realcaraudio.com/forums/archive/topic/11933.html
For some knowledge about how a thermostat works, check out the following:
How Car Cooling Systems Work
http://auto.howstuffworks.com/cooling-system.htm
Again, to paraphrase that famous board game: "DO NOT PASS GO. DO NOT
COLLECT $200. GO DIRECTLY TO YOUR NEAREST AUTO REPAIR FACILITY."
Good luck!
aht-ga
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