Need to replace thermo switch and thermostat in 95 Civic

I believe I've got a bad thermo switch/sensor in my 1995 Honda Civic LX. The
radiator fan does not come on when the AC is switched on (though the
compressor fan works okay). I checked the fan relay by putting 12VDC across
the coil and I hear a click, plus I get continuity across the contacts. I've
bent the pins in case the socket connection is bad. Shorting out the
contacts in the fan relay socket causes the fan to come on, so the fan
itself is okay. That's the disgnostic work I've done so far.

Thanks to Tegger's FAQ, I've been able to locate the thermo switch, but I
cannot figure out how to remove the connector for testing purposes. It's
rotated in such a way that I can't see do undo the connector, and help here?

Aside from the connector, are there any pitfalls I should know about when
replace the thermo switch? It's fairly easy to get to, so I should be able
to do it myself.

Also would like to change the thermostat, but never having done that I need
some assistance. First, in locating it. Then in determine what type it is
(med temp/high temp) and removal procedure. I've read that on later model
Honda's it's on the lower radiator hose but I can't see it.

 

Does the rad fan come on when the engine has been in heavy traffic for 5
minutes?

Warm it up all the way, take it to a quiet side street somewhere, and then
simulate heavy stop-and-go "inch forward" traffic for 5 minutes. If your
fan is not coming on, the temp gauge will begin to rise.

The thermostat is at the TOP of the engine, where the heat goes. The lower
hose is a long, snaky thing that goes from the bottom of the rad to the
thermostat housing. Follow the hose from the rad to the other end and there
it is.

WORD OF WARNING:
DO NOT INSTALL AN AFTERMARKET THERMOSTAT. Those things are much too likely
to cause you no end of grief. An OEM (and gasket) is less than $20.

There is only one rating of OEM: 90C/194F. DO NOT install a cooler one!

 

I'm confused. I was thinking that was the thermo switch/sensor, since it
labeled such on the FAQ:
http://www.tegger.com/hondafaq/overheating/overheating-index/index.htm
(photo next to "Thermo Sensor Check")

Are the thermo sensor/thermostat one and the same?

Also, tnx for the tip on using an OEM part, I'll be sure to do that.

 

I forgot to answer this part -- no the rad fan does not come on, whether
driving at speed for a while or stop-and-go. The temp guage doesn't rise to
much, no more than 1/3 of the way up.

 

Incorrect,

my Acura Vigor price for the thermostat was 86$ sale price, 110$ regular
price. Plus 11$ for gasket!

15$ at Canadian Tire... I still bought the OEM.

Adrian

 

The connector to the thermo switch has "lock" that must be raised about
1/16 of an inch before it can be unpluged. You may have to back the
thermo
switch a quarter turn or so to get to this "lock". The thermostat is a
couple
of inches to the right of the thermo switch an a bit higher. Be aware
that
there is still antifreeze in this part of the engine even after you
drain
the radiator. See Tegger's FAQ under radiator does not come on by
REMCO
for a lot of good data.
Ernie

 

Whooooa! Mine was $12 at the dealer. I've NEVER bought an OEM thermostat
for any make that was more than $20. Maybe I'm buying the wrong cars.

You won't regret it.

 

No. The thermostat is a big round mechanical thing about 2" in diameter.
It's inserted into the coolant stream and is supposed to block coolant flow
until a proper temperature is reached. The only way to change it is to
drain the coolant and remove the thermostat housing.

http://tegger.com/hondafaq/misc/thermostat.jpg

All the other things are electronic and serve to turn fans on and such.
They might tap into the coolant stream so they can sense the temperature,
but you can usually change them without draining the coolant.

 

Sounds like your thermostat may be going bad. You should be up to just
below the half-way mark on the gauge in less than ten minutes of driving.

How's your heater output?

The rad fan will NOT come on until the coolant temperature is high enough
to close the contacts in the fan switch. You may never be getting there.

 

DG, in your post refering to the photo in "Thermo Sensor Check"
The brass colored Sensor is the Thermo Switch. The wires under the
bolt to the right are ground wires. The bolt there holds the cover
to the thermostat, the hose on the right side of the picture is the
lower radiator hose. Remove this hose and another bolt(or two) and
the cover for the thermostat comes off.

 

Thanks, Ernie. I lifted the tab with a screwdriver and it popped right off.

I ended up running a wire from the thermo switch connector to ground, so the
radiator fan stays on when the car is running. I've already purchased the
replacement thermo switch, but need to go back and get a wrench big enough
to put it on.

One other thing I noticed was that the radiator was under pressure even
after 2-3 hours of sitting. Attempting to remove the rad cap cause coolant
to squirt out. I would have though any pressure would have dissipated during
that time.

 

damn. ida taken it out, got a part number off it then cross-referenced
online. its almost gotta be shared with something else.

then again, thats the wacky 5 cyl, huh?

 

Yeah, 2 or 3 hours does seem to be a long time for the radiator to
cool.
When I was having trouble with mine It would cool in an hour or less.
There could be a problem with the radiator cap or the line to the over
flow tank. When the coolant gets hot it should expand and flow into the

overflow tank and then be drawn back into the radiator as the engine
cools. I see a lot of talk about having air in the hoses or the engine
on this news group, but I don't know if that could be your problem.
I think the rad cap should allow coolant to flow to the overflow tank
at about 16 lbs pressure.
Ernie

 

Yeah, 2 or 3 hours does seem to be a long time for the radiator to
cool.
When I was having trouble with mine It would cool in an hour or less.
There could be a problem with the radiator cap or the line to the over
flow tank. When the coolant gets hot it should expand and flow into the

overflow tank and then be drawn back into the radiator as the engine
cools. I see a lot of talk about having air in the hoses or the engine
on this news group, but I don't know if that could be your problem.
I think the rad cap should allow coolant to flow to the overflow tank
at about 16 lbs pressure.
Ernie

 

I just replaced the thermo switch, and the radiator fan *still* doesn't come
on, even with the AC switched on (the AC compressor fan on driver's side
does come on).

I measured the new thermo switch by putting an ohmmeter across the terminals
and lowering it into a pan of boiling water. After the switch closed I got 1
ohm of resistance. The old thermo switch read 8 ohms. So I guess it was bad?

I'm not sure what else it could be.... shorted one side of the thermo switch
connector to ground does make the fan come on while the engine is running.
There's nothing else in the circuit as far as I know.

The temp guage never rises above 1/3 level (so far). Tegger, you had asked
about the heat output in the passanger compartment. At times, it seems to be
normal. Other times, it seems to be cool, even when the temp setting is over
at max. Could this be due to a bad thermostat or something else?

 

Personally, I think you're barking up the wrong tree here. 1 ohm or 8 ohms
means nothing. If the temp gauge never gets past 1/3, the rad fan WILL NOT
START NO MATTER WHAT.

If you simulated the heavy stop-and-go traffic like I said for AT LEAST 5
MINUTES, and the temp gauge DID NOT RISE, then your engine IS NOT HEATING
UP ENOUGH to make the fan come on.

I do believe you have a bad thermostat. Replace with new **OEM** for $20,
then report back, BEFORE you spend bigger bucks on the thermoswitch.

 

I don't believe the rad fan is supposed to come on when you turn on the
A/C. I have seen cars where the rad fan DOES come on with the A/C (e.g.
some model years of the Accord), but I don't think the '95 Civic is one
of them. The '94 wiring diagram does not show a direct connection
between the A/C system and the radiator fan. The only conceivable link
would be that the ECU could turn on the rad fan when using the A/C
(calls for A/C to turn on go through the ECU and the rad fan relay coil
is connected to the ECU in addition to being connected to the thermo
switch). I just checked the behavior of my '94 Civic, turning on the A/C
causes the condenser fan to turn on, but not the radiator fan.

It could be that you don't have a problem at all. This time of year, the
radiator fan on my '94 hardly ever comes on (Northern California, so not
very cold at all). Caroline (who now uses a different name in this NG)
once mentioned that when she did a coolant system bleed, it took a very
long time idling before the rad fan came on on her Honda.

 

If you've come to the conclusion of a faulty radiator fan circuit based on
activating the A/C, listen up. The radiator and condenser fan circuits are
isolated from each other. Not all Hondas run both fans simultaneously when
using the A/C system. Your year Civic does *not*. They occasionally
overlap in operation when normal engine fan cooling is needed with the A/C
running. So unless you're having other real issues with the cooling
system, save your money...

 

et...

Actually, I didn't know that. I read otherwise at
http://tegger.com/hondafaq/overheating/overheating-index/index.htm :
"Start the car and turn on the AC (if so equipped). Both fans (AC radiator
and regular radiator) should turn on.
If the radiator fan is not turning on, the relay, wiring or fan motor is bad
or power is not getting to the fan relay."

Anyway, I did have to replace the radiator since it cracked. The only money
I (possibly) wasted was installing a new thermo switch ($22) and I learned a
little in the process.

Good to know that another '95 Civic owner's fan doesn't come on with the AC
either. I'll just sit tight and monitor the situation before havnig any more
work done.

Thanks everyone for your help!

 

Hey Remco, is a revision necessary there?