I have a 92 Civic dx which is overheating. The radiator fan is not
coming on. I jumped it to the battery and it worked, so the motors
fine. I checked the relay and the fuses and all seem fine. I also
shorted the thermo switch plug and the fan came on, so the switch may
be bad, but it doesn't seem like any hot fluid is passing it. The
upper rad hose gets very hot, however the lower hose is cold. What
I've read is that if the upper hose is hot, then it means that the
thermostat is open, is that right? If so, why would the lower hose be
cold? It doesn't seem like any fuild is going through the lower hose,
but the thermostat is at the end of the lower hose. Does this make
sense to anyone? Am I misunderstanding this whole thing? Also I can't
get the damn bolts of the thermostat housing, they seem like they are
welded on, I tried a 13/ 32 socket and that cracked, so I went to
replace it and could find that size so I had to try a 10mm which seems
not as snug, but still the bolts don't budge. Any suggestions?
don't think so with the honda. the thermostat is on the "cold" side of
the coolant loop, so i think it works by having some of the hot bypass
the activation end of the thermostat. once the t-stat opens, that'll
regulate the resultant temperature mix passing through the pump and back
into the block. to answer your question however, it sounds like you
need to test the switch [rear side of the block and hard to get at iirc].
every bolt on a honda is metric. use quality tools to avoid breakage
and subsequent injury.
replacing the t-stat [with oem] is a good thing [don't forget to replace
the rubber gasket too], but i'm not sure it's necessary in this
instance. even if the t-stat's failed closed, the fan should still come
on because the switch is in the block, not the radiator. check all the
leads for good connection, in addition to fuses and relays. again.
Just to clarify,when you say "test the switch", which switch are you
refering to? the coolant temp switch?
also shouldn't the bottom hose aleast be warm? especially sense the fan
isn't working. it really seems like there is no fuild going through
that bottom hose. Do you have any thoughts on why that might be?
yes, the switch on the block that turns the fan on & off. /not/ the
temp sensors that the ecu or the instrument temp gauge uses.
it's winter - the bottom hose won't get very hot unless the engine's
working hard and will quickly cool again. and if your radiator's doing
its job. nevertheless, make sure the system has sufficient coolant.
look inside the radiator. if there's an air leak, the expansion bottle
doesn't give a reading on coolant level.
That would be utterly stupid.
The TS keeps the coolant *circulating in the BLOCK* until the motor reaches
temp,then the TS opens to allow coolant to flow thru the radiator.
Or do you think the water pump stops while the TS is closed?
not if you take a moment to understand what's going on.
it can't circulate unless there is a channel it can flow through. put a
valve on a garden hose - the water will NOT flow /regardless/ of which
end of the hose it's on if the valve's not open.
of course not! it's an impeller - there's no hydrostatic lock so it
can turn regardless.
besides, there /is/ a flow channel. go look under the hood at at your
civic's coolant pipes and describe what you see. then let's talk it
My Haynes manual for 94-00 Integra says if the upper hose is hot,coolant is
flowing and the thermostat is open,so your ECT (engine coolant temp)switch
is probably bad. You can check it with an ohmmeter(connector removed),it
should measure open with the motor cold,and shorted when the motor reaches
the proper temp,probably 180 degF(Integra GSR is 195 degF).You should check
the manual for your auto,it will give you the correct temp for your motor.
Torque settings for the TS housing bolts for my motor is 104 ft-lbs.
You may need a breaker bar and/or penetrating oil (*not* WD-40)to get the
bolts loose,the bolt is steel in a aluminum block,and corrosion may have
frozen the bolt threads. A 6-point socket(METRIC!) may be advisable,too.
Access was tight on my Integra,too.
I've found that cheap sockets are looser than quality ones.
haynes manual just regurgitates standard text. throw the wretched thing
away. the honda t-stat is on the cool side of the circuit - that should
be apparent just by looking at which hose it's connected to!
there are three thermoelectronic devices used on this motor:
1. the thermistor that feeds back to the ecu.
2. the thermistor that controls the temperature reading on the
3. the thermoswitch that controls the fan.
#3 is the ect.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.