88LX radiator fan always on

[AlaskaFestivaGuy]

I've read this:

https://fordfestiva.com/forums/showthread.php?59889-Cooling-fan-temperature-switch&highlight=thermostat

but the drawings are for FI, not carbie. Relays seem to be in different place on carbies than on FIs.

I've also read other threads.

PROBLEM: My 88LX fan runs continuously when ignition is on.

I have an identical (an 89LX) which behaves correctly (fan off, but goes on when I remove green wire from thermostat temp sensor). On 88LX, fan goes on as soon as I turn the key to the "on" position (without starting engine).

The adjacent yellow wire is connected to ANOTHER temp sensor. See attached photo.

QUESTIONS:

1. Why two sensors to sense coolant temp?

2. What (which sensor) has likely failed on my 88LX? I seem to recall having replaced the sensor to which the yellow wire is attached in the recent past to fix the fan-always-on problem.

[bravekozak]

This pdf will explain how the cooling fan relay functions.

[harpon]

Only ONE of those is a temp sensor for the gauge and the OTHER one is then the radiator fan SWITCH- which I think is usually GROUNDED TO CIRCUIT ON when it reaches a certain temp- but not sure about every model.

[zoe60]

The sensor on the thermostat housing is for the fan. I was just messing with mine the other day. If you unplug the wire with the key on, the fan should come on. Try hooking the wire straight to ground (bypass the sensor) and see if the fan goes off. This would indicate a bad sensor. If no effect, the problem will be somewhere else more complicated. Good luck.

[zoe60]

The sensor in the head is for the temp gauge.

[denguy]

I ended up direct wiring mine to an on-off toggle switch, just have to remember to turn it on when getting into stop and go traffic.

[AlaskaFestivaGuy]

bravekozk,

"This pdf" is the same 3-page pdf linked to by the thread I mentioned in my initial post, and refers to FId cars. My LX, of course, is carbed.

I'm not finding any C124 (Cooling Fan Relay) in my LXs in the area shown in your FI drawings.

Do you have similar drawings (and schematic) for carbed cars?

[ryanprins13]

Did you try grounding that connector?

Sent from my SM-G920W8 using Tapatalk

[WmWatt]

There are wiring diagrams for the different models in the back of the Haynes manual.

[AlaskaFestivaGuy]

My only Haines manual is 1,500 air miles away.

[WmWatt]

Haynes manual

pg 12-21 "Typical 1988 and 1999 engine control system (carbureted)"
cooling fan relay has yellow and red wire
coolant temperature switch has light green wire and black ground wire
coolant temperature sensor has brown and red wire and black ground wire

pg 12-26 "Typical engine cooling fan system"
coolling fan relay
one end of relay: engine fuse 10a hot in start or run dash fuse box - black and white wire
(with winding) powertrain control module - brown wire
other end of relay: hot at all times 30A engine compartment fuse box - white adn black wire
(with switch) coolling fan motor - yellow wire and black ground wire

Following diagram has a "cooling fan motor" but it might be air conditioning fan instead of radiator fan

pg 12-38 Typical 1988 and 1999 heating and air conditioning system"
air conditioning relay no 3
one end of relay: coolling fan motor - yellow and red wire
(switch end) black ground wire
other end of relay: air conditonoing relay no 2 - black and white wire
(winding end) black ground wire


What do you get for 1,500 air miles?

[bravekozak]

bravekozk,

"This pdf" is the same 3-page pdf linked to by the thread I mentioned in my initial post, and refers to FId cars. My LX, of course, is carbed.

I'm not finding any C124 (Cooling Fan Relay) in my LXs in the area shown in your FI drawings.

Do you have similar drawings (and schematic) for carbed cars?

Yes, I have the 89 EVTM. The layout and wire colors are identical, except the wire between the cooling fan relay and the coolant temperature switch is GN/R instead of GN/Y. I will scan and post tomorrow.

[AlaskaFestivaGuy]

bravekozak -- Thanks. And where are the relays in the carbie Festy?

WmWatt -- Thanks. 1500 -- actually, 1448 -- is Alaska Airlines' published distance from Seattle-Tacoma Int'l Airport to Anchorage Int'l Airport. It's about 1,000 more miles by road and takes a week vs. 3 hours.

[bravekozak]

Left front of engine compartment in front of coolant recovery tank.

[AlaskaFestivaGuy]

So I finally replaced the temp sensor switch in the thermostat housing with a new one (about $45 from O'Reilly) and got this:

1. When I turned key to ON, fan (correctly) did NOT start.
2. When car warmed up to mid-range on the temp gauge, fan started and ran for a few minutes and stopped as temp gauge came down a bit.
3. I stopped engine, figuring problem fixed.

So I figured -- "Let's do that again, just to be sure."
Everything as above, but fan never turned on. Radiator started steaming, so I stopped engine and let it air cool.
When I remove the temp sensor switch wire and turn key to ON, fan (correctly) does not start.
When I replaced the wire and started engine, it still runs fine. I did not let it overheat again.

So what gives? Was the temp sensor switch bad and something else just picked NOW to fail?