To clarify a bit,

the car overheats when it is sitting idling. If I'm driving over 30 or
40 mph the temperature comes back down.

Thanks,
Andrew

How did you determine that? Just checking for drips underneath the car isn't
enough -- for example, a leaking head gasket could leak coolant into the
combustion chambers where it will be evaporated and blown out the tailpipe,
and you'll never see any drips. Have you verified that the cooling system
actually is, and remains, full?

Why?

I doubt it.

It's possible that a failed temperature sensor is causing overheating by
preventing the electrically operated fan from coming on -- but as long as the
vehicle is moving at any appreciable speed, there's enough air being forced
through the radiator that the fan isn't really needed for cooling, so this is
unlikely IMO unless you're doing a lot of driving in very heavy stop-and-go
slow speed traffic. The more likely symptom of a failed sensor is a gauge
that's *falsely* reporting the engine to be too hot, when the temperature is
actually normal.

IS the engine actually overheating? (Noticeably hotter than normal when you
lift the hood, smell of hot coolant, wisps of steam drifting out from under
the hood, clouds of steam pouring out, etc.)

If so, I'm betting the problem is a failed thermostat. *Especially* if the
thermostat wasn't replaced at the same time the radiator was. (It should have
been. They're cheap, and they fail fairly regularly in older vehicles. As long
as the cooling system is drained anyway, it's just silly not to replace it.)

I agree. :-)

It is not. The temperature sensor does just that: senses the temperature, and
sends a signal to the temperature gauge. The thermostat controls how hot the
engine gets; specifically, the thermostat is a valve that sits between the
engine and the radiator. It stays closed until the coolant reaches the correct
temperature (190F, I believe), and then opens. This prevents water from
circulating through the radiator until the engine is warmed up.

If the thermostat is stuck open, the engine takes a very long time to warm up
(which is bad in a variety of ways) -- and if it's stuck *closed* (or doesn't
open fully), the engine overheats. Of course, that's also bad. :-)

If you have the same Haynes manual that I do, it's on pages 3-2 and 3-3.
Or you could look in the index under "Thermostat, check and replacement".

The instructions for checking and replacing the temperature sensor are a few
pages later, listed under "Coolant temperature sending unit - check and
replacement".

You should be able to find a thermostat for your car at just about any auto
parts store, or maybe even in the automotive department at Wal-Mart.

From your description, remember I am not there to do the work, so this
is all guessing, and isn't a How-to:

Something with coolant flow must be happening.  If you have a fan
comeing on, and coolant level is sufficent, I would suspect coolant
flow is the issue.

I would check the water pump for operation, the dumb way I would do
it, is check if I get heat (strong heat) from the heater.  Second, I
would then figure what could be interupting flow, and the internal
coolant thrmistat (a valve that opens and closes allowing flow to the
radator).  I would be suspect of that, since I've been told they fail
over time.  

I was once told how to check one, a valve thermistat, but figured that
once I open the housing, it saves time to just install a new one.

If a person can safely work yourself, and follow directions from the
Haynes book, I like them better than chiltons, since more pictures. :)
A person could replace the item themself.

later,

tom @ www.NoCostAds.com

Hi everyone,

Thanks to all that responded and helped me figure out the overheating
problems. The car is now happy.

Thanks again,
Andrew