The Diesel Garage banner
1 - 16 of 16 Posts

·
Junior Member
Joined
·
132 Posts
Discussion Starter · #1 ·
Is it a sensor causing the fan not to turn on when the water temp. climbs? It works when I turn it on manually, but it won't come on automatically, with or without heat on in the cab. It's a '93 379 3406C 3ZJ. Is it the sensor at the thermostat housing, or does an oil temp. sensor activate it? I would think it's the water temp. sensor, but I'm not sure. Happy Easter to every one.
 

·
Member
Joined
·
168 Posts
Mine(Ford) is old enough to not have sensors. In my case its a "shutter" valve, a thermostatically controlled air valve that controls the pressure to the fan clutch. Its not that expensive but on my truck an sob to get to. On mine its down low under and behind the alternator and all the brackets near the bottom of the water jacket. ALL the coolant has to be drained or Ill have a mess and once that is done Ill need someone with small hands to reach back in there to twist in out and back in. Hooking up the air lines is another b!tch of a job. For me, hooking up a couple wires to a switch was a 5 minute job.
 

·
Senior Member
Joined
·
2,557 Posts
The fan temp switch should be on the head at the front , it is 2 wire screw terminal , the guage sender will be there too , it is one wire screw terminal, the actual fan solinoid is on the fire wall , where it can get a electrical signal from the temp switch(engine coolant temp,usually 200*), the A/C trinary switch(refridgerant high side pressure) & the dash switch (you know that works)

to test hook a jumper wire between the terminals at the head switch, this should turn the fan on. (I have a 10 amp inline fuse in a jumper wire in case of short circuits, saves smoking wires)
 

·
Junior Member
Joined
·
132 Posts
Discussion Starter · #4 ·
The fan temp switch should be on the head at the front , it is 2 wire screw terminal , the guage sender will be there too , it is one wire screw terminal, the actual fan solinoid is on the fire wall , where it can get a electrical signal from the temp switch(engine coolant temp,usually 200*), the A/C trinary switch(refridgerant high side pressure) & the dash switch (you know that works)

to test hook a jumper wire between the terminals at the head switch, this should turn the fan on. (I have a 10 amp inline fuse in a jumper wire in case of short circuits, saves smoking wires)
So you're saying the solenoid on the firewall must be good because it's accepting signal from the in-cab switch? If the temp. switch is bad should I drain the coolant out before replacing it?
 

·
Junior Member
Joined
·
65 Posts
My '89 379 the signal from the manual switch just y ties into the temp switch wire. That is the factory setup on mine.
i would check to make sure that one terminal on the two wire fan temp switch is hot if it is jump across it and the fan should come on.
 

·
Junior Member
Joined
·
1,811 Posts
So you're saying the solenoid on the firewall must be good because it's accepting signal from the in-cab switch? If the temp. switch is bad should I drain the coolant out before replacing it?
If you are fast enough, you will only lose about a half a quart...but it is messy. I try to be quick and change it out, instead of draining the coolant just for that.

Like was stated, take a screwdriver or anything and cross the posts on the fan switch. If it comes on, it does not mean the switch is bad. Are you sure its getting hot enough to make it come on? During the winter, some of mine never came on because the temp never got hot enough.

Yours should come on around 205 degrees.
 

·
Junior Member
Joined
·
132 Posts
Discussion Starter · #8 · (Edited)
If you are fast enough, you will only lose about a half a quart...but it is messy. I try to be quick and change it out, instead of draining the coolant just for that.

Like was stated, take a screwdriver or anything and cross the posts on the fan switch. If it comes on, it does not mean the switch is bad. Are you sure its getting hot enough to make it come on? During the winter, some of mine never came on because the temp never got hot enough.

Yours should come on around 205 degrees.
I had the water temp. light come on about 200 degrees. Fan never turned on so I did it manually to cool the motor down and the light went out. But if I'm getting an accurate water temp. reading wouldn't that mean the temp. sensor is ok?
 

·
Junior Member
Joined
·
1,811 Posts
I had the water temp. light come on about 200 degrees. Fan never turned on so I did it manually to cool the motor down and the light went out. That's what leads me to believe the sensor is junk.
You may have a gauge not reading correctly. The fan should engage around 205, and the light at 208-210. May need to check temp with a temp gun or manual gauge.

The sensor could very well be junk...I was just wondering if was actually getting hot enough to engage the fan.
 

·
Junior Member
Joined
·
1,811 Posts
I had the water temp. light come on about 200 degrees. Fan never turned on so I did it manually to cool the motor down and the light went out. But if I'm getting an accurate water temp. reading wouldn't that mean the temp. sensor is ok?
I've never been a big fan of electric temp gauges. KW came out with a manual gauge about 10 years ago, and now all of mine have it.
 

·
Junior Member
Joined
·
132 Posts
Discussion Starter · #11 ·
I just posted on that the other day. Like your 3406c mine is also a 3zj and has a Horton fan and electrical controls. Click here for diagram and full discussion:

http://www.thedieselgarage.com/forums/showthread.php?p=1075862#post1075862

Roger
I apologize to all of you guys for my ignorance. I'm not very good with electrical components. But I see in this diagram that everything ties into the switch. I'm not really clear if a switch can cause this problem; not just a temp. sensor. Is there possibility that the switch can go bad even though it works ok manually? I'll be going to tomorrow morning to test it.
 

·
Junior Member
Joined
·
1,811 Posts
I apologize to all of you guys for my ignorance. I'm not very good with electrical components. But I see in this diagram that everything ties into the switch. I'm not really clear if a switch can cause this problem; not just a temp. sensor. Is there possibility that the switch can go bad even though it works ok manually? I'll be going to tomorrow morning to test it.
No apology necessary.....the fan solenoid has a hot and ground. The hot, as stated, is tied in with the fan sensor in the head, the manual switch in the dash, and the high pressure sensor in the A/C system. If the high water light is coming on at 200, either the gauge is reading wrong, or the high water sensor is going bad.
Buy or borrow a laser temp gun and shoot the thermostat and surrounding areas when the high water light comes on. If it reads 200, along with the gauge...the high water sensor is bad. If it reads higher, then both the sensor and gauge is bad, depending on the actual temp.
 

·
Member
Joined
·
168 Posts
Electric gauges suck. On my old truck I fought an overheating problem for quite some time. Changing the T stat didnt seem to help. A ground wire from the cab to the engine fixed me right up.

On my current truck Ive noticed that my truck runs very warm when my headlights are on. Just turn the lights off and watch the temp go down.
 

·
Senior Member
Joined
·
2,557 Posts
the other possibility is that the warning light sender is in a hotter spot than the fan switch, some times the warning sender is in the hole in the center of the head by the turbo, and this area can get 10 or better degrees hotter than the front of the engine. My 3ZJ will turn the warning light on at 220, but under hard power the warning light comes on before the fan comes on, so if it's pulling hard I switch the fan on manually. If you think of electricity like a fluid flowwing in the wires and the switches like valves, sometimes it is easier to understand.

the nomenclature NO stands for normally open (off) , meaning the switch or solinoid will NOT pass power unless a trigger is applied. NC, normally closed (on) means the switch or solinoid WILL pass power until a trigger is applied.
 
1 - 16 of 16 Posts
Top