Idle Overheating- 1993 Honda Accord LX
 

After running the engine for about 10 min the engine temp needle will slowly begin to creep up. I've checked to see that the fan is op and it is. Replaced the engine coolant temperature sensor thinking that may have been the issue (no reading on the multimeter when tested) and I still have the same problem. When it begins to overheat sitting at idle I can place it in park, step on the gas, and the gauge needle begins to move down. Is this a thermostat issue? Thanks.

Does both the radiator fan and A/C condenser fan run at the same time?

When the AC is on, yes they both run at the same time... but at no time does either fan turn on at idle.

The fan switch is at the thermostat housing - towards the back & below the throttle body. Unplug that & jumper the 2 terminals on that wire with a paperclip or something. Key-on, that should make both fans run. If that works, then you might suspect the switch. When the engine is running hot, measure continuity between the 2 terminals on the switch. The switch should close (and the fans run) when the temperature gauge gets somewhere above 50 or 60%.

Incidentally, what did you replace? The ECT sensor is on the head near the distributor, with a 2-wire plug. The sender for the temperature gauge is also on the head, with a 1-wire connection.

There's also another fan switch in the upper radiator-hose nozzle at the head. That's got authority to run 1 of the fans, after you switch off the engine. It goes through a fan-timer module which we can describe more depending on what you see with shorting the fan switch.

"jumper the 2 terminals on that wire with a paperclip" I did this and the fans run. I replaced THAT switch thinking this was the issue because when pulled I didn't get any readings from it on the multimeter.

"That's got authority to run 1 of the fans, after you switch off the engine." The fan does run for sometime after the car has been shut off but not for very long.

Fan switches aren't going to give a resistance signal all the time, like the ECT sensor. It's a switch that is open-circuit until the temperature gets above their setpoint when the switch closes.

The fan timer is supposed to allow the 1 fan to run for something like 10 or 20 minutes. If that fan switch is stuck, the timer stops the fan from draining the battery by running forever. If the fan runs for a minute or 2 after you shut down, that sounds like the switch is OK.

The other switch (thermostat housing in the back) can be tested by sticking in a pot of boiling water. That should close the contacts & show continuity. Someone probably knows the actual temperature setpoint, for checking against a thermometer as you heat up a pot of water.

But another thing crossed my mind... How long since the antifreeze was changed & the system rinsed out? If there's crud in parts of the radiator, maybe it doesn't flow as well as it should? (the car IS 25 years old...) There's cleaning products you can buy to put in there, run the engine to circulate & heat it, then dump out & rinse the system.

Some of the same information is in this thread...
https://www.hondaaccordforum.com/for...sensors-39096/

I haven't done a flush of the system since buying it in in 2014. I'll give it a clean a see how that works.

Does stepping on the gas in park push coolant through the system more... in turn making the temp drop as fast as it does? I just don't want to screw it up anymore than it is right now.

What is the part number on the switch that you replaced?

Duralast SW546

Raising the RPM does pump more coolant around the engine & radiator. That's the thing, it sounds like it needs that, and just idling doesn't give you enough flow. That's why I suspect(?) crud blocking something.

There's no such thing as too much flow - the thermostat is supposed to control that. If the system starts to over-cool, then that means your thermostat might also need replacing. Not much money, but the pain of draining & refilling when you change the T-stat.