So from looking at my own 91 Civic's temp gage, I see yours
went about 3/4 of the way between "C" and "H." Your Civic
definitely overheated. The only thing I can say with
confidence is that the chances of a blown headgasket go up
with each overheating episode.
My thermostat seemed to be working fine when I pro-actively
changed it at 151k miles. First because it's very
inexpensive to put in an OEM one. Second because, from
general reading, I expect most cars go through at least one
thermostat in their lives. Third, from general reading, many
folks do pre-emptively change their thermostats.
There are tests one can do on a thermostat but given how
cheap it is, I'd just slap a new one in. Always go with an
OEM thermostat. The cost difference is small, and one will
then have the confidence that they have precisely the
correct design temp settings on the thermostat.
Also, FYI, c. early 1990s Hondas are usually on their second
radiator by now. So yours could be said to be par for the
course. IIRC leaks at the radiator top are a common cause
for replacement. Aftermarket radiators are fine.
I suggest you do a proper air purge (if you can handle a 10
mm wrench, you can do this) of the coolant system, monitor
the coolant levels, and report back. See autozone.com's free
online repair manual (or your owner's manual) for the
directions for purging. Have a magazine while you wait the
40 minutes or so for the fan to come on twice. Only use OEM
coolant (or maybe orange Havoline). Hopefully your mechanic
used OEM coolant.
Thanks for the reply. Correct, a new head gasket was put on.
thermostat stuck, and the engine did overheat, but never
that is possible). The temp gauge was at the top of the
symbol when noticed instead of at the bottom of the symbol,
gauge never went to the top of the range (not sure if this
beyond" or significant). But after the thermostat stuck, it
replaced but the head was not skimmed, the bubbles were only
about 6 months later and the real reason the head was
because the top of the (good condition) radiator sprang a
prompted the mechanic to look for a cause. Mechanic said
pressure in the main hose was the cause of the leak as
too high and would land up bursting the hose while on the
As an aside, how does one predict a thermostat sticking,
pro-actively just change thermostats like cam timing belts
change them after X kms regardless of whether they are
signs of packing up?