Electric fan not kicking on.......

[Evil95GT]

Ok, so the coil problem is figured out, so we decide we're going to take the '95 out for the first drive after hooking up the gauge cluster. Well, we start the car and let it idle, to make sure the fan works. The gauge creeps up to "M", and it has NEVER ran that hot. Then it gets to "A", then a little past the "A". So, I turn it off, and try to figure out what the hell is going on. Well, we found out there was an air pocket in the cooling system.  My question is.........would that cause the fan NOT to kick on/off? I'm really hoping that's what it is. Thanks in advance.

[W.O.T. Stang]

Ok, so the coil problem is figured out, so we decide we're going to take the '95 out for the first drive after hooking up the gauge cluster. Well, we start the car and let it idle, to make sure the fan works. The gauge creeps up to "M", and it has NEVER ran that hot. Then it gets to "A", then a little past the "A". So, I turn it off, and try to figure out what the hell is going on. Well, we found out there was an air pocket in the cooling system.  My question is.........would that cause the fan NOT to kick on/off? I'm really hoping that's what it is. Thanks in advance.

My car is doing the same thing at the moment... cause the cap is loose to keep pressure from building up, since i have no overflow bottle.

It's like this... when you have air in the system it travels thru and gets warm... but air transfers less heat then the coolant does.  The fan is set to come on at a predetermined temp.. well say it's 220º.. if air is going by, it's not going to be a constant 220º as if it were coolant.  The air is going to be cooler and vary a lot in temp,  which is why the fan wont come on.

Like I said, mine is doing the same thing as we speak.  Air pockets get in the system, and the temp sensor for the gauge realizes the block is getting that hot (Which is why it went up to the A) but the radiator (where the sensor for the fan to come on is) is full of air, which is colder.  So it wont turn the fan on.  Follow me? 

The best way to get rid of air in the system is to leave the cap off and let it warm until the thermostat opens.  You'll see air bubbles coming out when it opens and when they stop, put the cap back on and then try it again.

[Evil95GT]

Ok, the air pocket is gone. Guess what! Fan still doesn't come on. We just pulled the T-stat.....I'll keep you all posted. 

[Blue87GT]

I'd bet some money (not too much) that the ECT sensor is either unplugged or is bad.  That it what reads the coolant temp and kicks on the fan accordingly. 

Also, I know this sounds dumb, but check the wiring/plug on the fan itself.  The plug sometimes overheats and shorts the harness.

[Evil95GT]

I'd bet some money (not too much) that the ECT sensor is either unplugged or is bad.  That it what reads the coolant temp and kicks on the fan accordingly. 

Also, I know this sounds dumb, but check the wiring/plug on the fan itself.  The plug sometimes overheats and shorts the harness.

This is *so* bad, guys. We replaced the thermostat, and it's STILL overheating. I'm seriously hoping it's that sensor. I figure I'll just try to start with the cheap first. Hell, the fan worked last time it was in use (April). I'm at a total loss here, and I'm starting to get disgusted again.

[Blue87GT]

Try bypassing the switch at the fan like this.

http://www.allfordmustangs.com/Detailed/499.shtml

Hopefully your an will work like this.  Also, the ECT sensor is pretty cheap at Autozone, etc.

[Evil95GT]

We're definitely gonna try that tomorrow. Thanks for the link! 

Dumb question, but could any of this be going on because I'm lacking a coolant bottle? We were thinking that maybe there isn't any way for the system to express air or overflow, and maybe that could be a factor?

P.S. Remember what I said about how you'd have your chance to help people? See, ya just did! 

[W.O.T. Stang]

Dumb question, but could any of this be going on because I'm lacking a coolant bottle? We were thinking that maybe there isn't any way for the system to express air or overflow, and maybe that could be a factor?

Re-read what I typed above.  If the hose is not connected to anything, it's sucking up air.  If it is hooked up and plugged, you have an extreme amount of pressure in the cooling system then normal.  Also, was the wire that used to be used for a manual by-pass on the switch ever get hooked back up (maybe the wire it went too that probably controls the fan is broke from tapping into it?  It's VERY hard to say without seeing it.)

I'll talk to you more about it tomorrow if you want me to help.  Too much to type here.  Remind me!

[Aussie XAXB]

W.O.T. Stang about leaving the cap off and watching the flow when the thermostat opens. Also be SURE that your heater is on and on high. You want to be sure to fill the heater core too in order to purge any air there.

I would look up the resistance specs on the temp sensor. You might have to take it off the car to get an accurate reading.

With a totally enclosed system you will be building a higher pressure than the system was designed to withstand. I would go with an overflow and recovery system regardless.


Steve