91 Civic Overheating

Hi,

I have a 91 honda civic with 232,000 miles. Radiator is about 1 year old.
Recently I noticed the temp gauge running all the way to the red then
dropping to about half only to repeat the pattern over and over. It was
almost as if the themostat was working but at a high temperature range.
Sooo.... I bought a new thermostat and replace it (old one didn't look bad
at all). No change. There is plenty of coolant, no strange noises or
leakage, turning on the heat doesn't seem to affect the pattern.

For now it seems like it works but just "late". But it has been below
freezing and it doesn't seem like a good idea to rely on a car that has
these symptoms.

I noticed the fan is on when I park but have no idea how well it is working
while driving. Could the fan be coming on late? I find it hard to believe
that the fan could drop the temperature immediately when I'm driving 50mph
at 25 degrees.

Any suggestions?

Thanks

 

I had an '89 Toyota that had the same problem. What I found out is that
there were 3 different temperature sensors/switches that are used to send a
signal to start the fan and one of them was not working (the one that was
used the most by the system).

 

Your engine could be fine but you'd have to check. There's a TSU
(Temperature Sending Unit) that is usually located on top of the thermostat
housing. Check that and make sure it's working properly. Since the fan is
coming on that means the thermostat is working fine. It might be a messed up
gauge that doesn't display the correct results. Try cleaning up the contacts
and see if that helps. If not a replacement should fix it.

--Viktor