Temperature gauge pegging when I stop...

1993 Accord LX 4-door sedan. I already know about the main relay.

When I stop and turn off the car, especially if I've been driving hard
or a long uphill trip, the cooling fan comes on. (Normal, I think.)

Today, I was running errands, made a few stops close together, then got
stuck in traffic and noticed that the temperature gauge had pegged at H.
As soon as traffic started moving, the needle went back down to a nice
normal reading. Stop again, up it goes, start again, down it goes.

Now, aside from the entertainment value, and the thrill of not being able
to tell whether my engine is about to melt... I think I could live without
this particular behavior. I've looked over the shop manual, and am
guessing these possibilities:

1. Ye olde thermostat is about ready to be replaced.
2. A fan should come on when I stop, but doesn't (because of #1?)
3. There's some kind of cooling system blockage, only when I'm stopped.
4. My coolant:water ratio exceeds 60% and I'm getting decreased cooling.

The car's due for its annual safety check this month anyway, so it'll be
visiting the mechanic who does that check. I figure I'll have him give
the thermo a look, and maybe refill the coolant if the thermo isn't the
issue. Logical? Insane? Anything else I should have him look at?

Thanks for any thoughts,

-Dan

 

My vote is #2, but it is not due to a thermostat problem. You probably
know this, but the thermostat is a mechanical device that directs
coolant through the radiator or bypassing the radiator according to
temperature. It has no electrical connections and has only indirect
influence on the radiator fan.

There is a thermo switch (Honda calls it an ECT switch, or Engine
Coolant Temperature Switch) that controls the fan. From a poor line
drawing it looks like it is sitting high up on the engine, left hand
side. If the drawing I have really is for the '93 Accord (the file name
says it is '93 but nowhere in the document is there a year listed) it
seems the wire colors are YEL/GRN and BLK. A simple test would be to
disconnect the wires from the ECT switch and turn on the ignition (do
not start the car). Then short the two BLK and the YEL/GRN wires. The
radiator fan should now come on. If it does, there is a good chance you
have a broken ECT switch. If the fan does NOT come on, likely suspects
are fuses or the radiator fan relay (somewhere around the right
headlight). To test the relay, turn off ignition and unplug the relay.
Short the BLU and the BLK wire together. The fan should come on. If it
does, likely a bad relay. If it does not, blown fuse or a bad fan motor.

US models have a fan control module, but from the wiring diagram it does
not seem that a faulty module could preclude the rad fan turning on. It
is my understanding that the rad fan control module controls how long
the fan can run after the ignition is turned off, but the wiring diagram
shows only the condenser fan (not the rad fan) being able to run with
ignition off. Canadian models do not have the after-run feature on
either fan.

 

1. yes, replacing ye olde thermostat is a good thing.
2. the fan switch could be faulty - remove & test. it should be a big
plug screwed into the rad with 2 wires coming from it. also, check
operation of fan by shorting those 2 leads you've just unplugged.
3. possible, but low on the list.
4. very unlikely.

also check for ye olde insectes stuck in the rad. i've seen them
clogged to the point that driving less than 50 has the needle well into
the red.

if this is a suddenly recent condition, check item 2 first, then 1.

 

Not low on the list at all for a 93. A few years ago, my 92 Civic Si
had a crudded up radiator that did the exact same thing. New radiator,
and all was well.

Partially blocked cooling passages give the very symptoms you describe.

 

Randolph, Jim and Elmo,

Thanks for the replies! As I said I was going to do, I took the car in
for its annual safety check and asked the mechanic to check the cooling
system while he was at it. He drove it around a bit and couldn't make
it overheat (which isn't surprising, since the problem had been somewhat
sporadic), but did find a couple things that warranted replacing - the
thermostat and the radiator cap. Both due to 11-year-old gaskets just
wearing out. The thermostat was going kind of "halfway" or something
(half open? half closed? is the glass half empty or half full?) and
the radiator cap wasn't holding pressure (which could also be a bit of
an issue... so he replaced both of those. The car seems to be back
to its usual extremely well behaved self.

The electrical stuff, incidentally, checked out fine. Oh, and it passed
safety with no problems, yay.