89 wagon - unplug rad fan switch, fan comes on

[doublethink]

My issue is the fan doesn't come on as the temp climbs at idle, it moves the temp above middle on the gauge, and it only comes on when I unplug the sensor below the dizzy.

I'm trying to verify 2 things, if you guys can help me out.

The single wire sensor below the dizzy on this motor (89 wagon carb)

1) This is the fan switch correct?

2) How does this circuit work, does it rest at ground and then "open" when the switch clicks above a certain temperature? Or is it the other way around.

Thanks.
-Mike

[REN69]

Chances are the sensor is fine and all you might need is to change the thermostat, try that first and see what happens.

My fan barely ever comes on, as long as the car is not overheating you should be ok.

[doublethink]

Originally Posted by REN69

My fan barely ever comes on, as long as the car is not overheating you should be ok.

Well when the cluster climbs to almost 3/4 i consider that cause for alarm, especially since its still 50 degrees out.

I figure once its 90 out im in for a world of hurt, plus ill blow a headgasket awful quick running overly hot too.

For example, today I ran the car with the interior switch to COLD closing the heater core, and let it idle for 10 mins or so.

Watching carefully it was holding steady at just under center, like 40%, where I perceive it should be under normal conditions.

Then, 15-20 mins in it began to climb to almost 3/4, with no sign of the fan coming on. I gave it a good 5 minutes to do something, it didn't. So i unplugged the switch, the circular metal relay labeled FAN clicked, and on came the fan.

And I watched the temp go back down to 35-40% on the needle.

I strongly suspect the sensor is toast, but Ill change the thermostat too if I'm going to be draining the coolant anyway. Also, upon a forum search on here I encountered a thread where poor coolant flow to the switch itself could be a culprit for this, but I hope this water pump isn't goin

But my question remains, is the ground supplied by the fan switch on the block supplying 85/86 on the fan relay with ground to cut power to the fan, (open) or supply it (closed)?

Its a non standard relay for some annoying reason, so I don't know which is 87 and which is 87a.

It would help me to know how this circuit is supposed to work, and at what temp the fan should kick on oem, because I can visit a mechanic friend of mine and do some tests with his thermometers and my multimeter.

So for now my to do list looks like this:

1) fully drain the system
2) replace fan switch
3) replace thermostat
4) flush system
5) refill and properly bleed

And cross my fingers that my water pump is ok.

Thoughts?

[retiredat44]

has any work been done on the car lately? Myabe cooling system work? Just wondered if someone had drained and/or refilled the water/coolant. There could be an air pocket by the sensor. Allso, a sensor could be bad. The sensors are not cheap.

[doublethink]

Originally Posted by retiredat44

has any work been done on the car lately? Myabe cooling system work? Just wondered if someone had drained and/or refilled the water/coolant. There could be an air pocket by the sensor. Allso, a sensor could be bad. The sensors are not cheap.

Well the list at the dealer was expensive, but autozone had one that wasn't too bad.

I'm going to try flushing and bleeding first.

No work has been done since I bought it. All I did was check the coolant level, which is fine.

Also the heat works very well, and both upper and lower rad hoses are equally hot when at full operating temp, which originally steered me away from air pockets, but ill try that too, since it doesn't cost anything.