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Hey all. Long time no post.I've been working on another (non-Vette) project.i wired up a dual fan system in my Mustang and can't get it working right. I am grounded from the fans to the frame. The other ground would be either of the 2 temp senders i have on the block( one in the water neck, one on the back of the intake manifold). The car will get to over 200 and neither of the fans will come on. My senders are 185 and 200 degrees. I've followed the wiring diagrams exactly, but i can't get a fan to come on unless i jump the ground from the senders to a ground on the block. I'd love ideas if anyone had any.
OK. Sounds pretty simple and like your halfway there.
If you remove wire from temp sender. And ground it and the fans run. Then your wiring all sounds good.
Your problem is obviously with the temp senders. Sounds odd that they both would be bad. But it's a possibility.
First, How did you install them? They need a ground path to the intake or head. Did you put sealant of some sort on them preventing them from getting a good ground?
You can test them by putting them in boiling water with an ohm meter connected to them and a thermometer in the water. When they reach temp they should close the circuit and your ohm meter should go to zero or very close to it.
First thing I would check is that the threads in the head and intake are clean. As well as the threads on the senders. These are a tapered pipe thread. Use no sealant.
I'm at a loss on the senders. One is in aluminum manifold, the other is a steel water neck. No sealant on either. I was not quite to the point of boiling them. I figured there was some common denominator I'd overlooked. 
Have you tested the ground going to the block and to the aluminum intake manifold is good? Use a volt meter set to “continuity” then place one lead on the ground point (terminal lug) on the engine, touch the other meter lead to the bottom brass metal of your temp sensor. If you get a buzz or continuity reading (numerical display on meter) then the problem has to be the sensor, but that seems really bizarre that both new sensors would be bad out of the box. Is aluminum a good electrical conductor. On my Edelbrock Carb someone ran a ground wire to the carb for the electric choke, I have an aluminum intake manifold.
I used that type of thermo sensor to run my fans for years. Installed in the intake manifold with no issues. Now my EFI computer runs the fans but it's temp sensor is in the same hole. Aluminium is a very good conducter.
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Is your temp gauge accurate? Is your system designed to use 2 temp senders?
It sounds like your gauge isnt accurate or your senders arent supposed to come on until 195. You may just need different senders
If you short the sender from stud to body, does the relay trip? If so, it is a heat range issue. If not, your ground, or understanding of the switches, is the issue.
If the noise of two fans starting/running at full power is an issue or the spike on the electrical system too much you might consider a DeRale PWM Electric Fan Controller.
I have a Holley EFI system that can activate the two fans individually or together but I still prefer the quiet inside my Corvette. The DeRale system starts the fans up at 50% speed/Power and slowly ramps up the speed if the engine continues to get hotter. It uses a single sensor mounted/attached near the Return hose on the radiator and it watches the temperature of the coolant coming back to the engine. There is a tiny adjustment screw built into the controller to set when the Fans come on (at 50%) and you can set it to hit 100% wherever you like. The benefits are many and the system works great on cars with loud electric fans. Less wiring and way less noise....
On my C3 the two Spal 11" electric fans would draw over 35 amps at full speed when they were activated. In a convertible it was too much noise having both fans start up at 100% even for this old man who is hard of hearing. I like listening to my BB 427, not the cooling system.
Silly question, but is your engine properly grounded to the frame?
All the best connections between sender and intake won't help if the engine itself isn't grounded well to the ground plane that the fans are grounded to (which is presumably the frame).
If the noise of two fans starting/running at full power is an issue or the spike on the electrical system too much you might consider a DeRale PWM Electric Fan Controller.
I have a Holley EFI system that can activate the two fans individually or together but I still prefer the quiet inside my Corvette. The DeRale system starts the fans up at 50% speed/Power and slowly ramps up the speed if the engine continues to get hotter. It uses a single sensor mounted/attached near the Return hose on the radiator and it watches the temperature of the coolant coming back to the engine. There is a tiny adjustment screw built into the controller to set when the Fans come on (at 50%) and you can set it to hit 100% wherever you like. The benefits are many and the system works great on cars with loud electric fans. Less wiring and way less noise....
On my C3 the two Spal 11" electric fans would draw over 35 amps at full speed when they were activated. In a convertible it was too much noise having both fans start up at 100% even for this old man who is hard of hearing. I like listening to my BB 427, not the cooling system.
Best regards,
Chris
I second the derale setup, I have the older controller with my dual 11" fans (normally the 11" spals draw about 14 amps each for a total of 28-30amps) My controller turns one fan on 15 degrees before the second so most the time the second fan never even turns on. mine does not do the pwm function though which would be nice as well.
Silly question, but is your engine properly grounded to the frame?
All the best connections between sender and intake won't help if the engine itself isn't grounded well to the ground plane that the fans are grounded to (which is presumably the frame).
I thought that too until I read he got the fan to turn on when grounding the sensor wire to the engine. OP are you sure your coolant is flowing correctly? if the system has air in it maybe the sensors arent getting to temp in the same manner as your gauge sensor?
Silly question , but you did connect the water pump belt thats missing in your photo right?
OK, you said the fans come on if you ground the sensor to the block. How about if you ground it to the head, or to the intake? Where it works and doesn't work tells you where your ground plane is interrupted.
Then you can decide if it's worth it to chase that interruption, or just run an aux ground wire from the appropriate spot on the engine to the frame.
If it doesn't work to ground either the head or intake, that only leaves the sensor thread itself as the culprit (for the sensor in the intake -- the one in the t-stat housing adds another potential ground interruption point).
Oh, and make sure you are cleaning to bare metal when checking grounding.
Hey all, sorry i had notifications off and had no idea there were any replies to this thread. I appreciate everyone's advice and wouldn't just ignore it.
On the ground question...i have this block grounded. There's a cable from the ear under the passenger head to the frame. I can stick a test light anywhere on the block and get continuity from the positive on the battery to the block, with the exception of the aluminum manifold and the steel water neck. I get no continuity there. I do get continuity off the bolts holding these 2 parts on. To be fair, there is paint on the outside of these parts, but the threads are not painted.
i did bring my senders in and tested them in boiling water. They both show continuity ( with the ohmmeter) at their respective temperatures (200 and 180 degrees) and once they cool off, i can hear the senders open back up and continuity fails back to open.
I thought that too until I read he got the fan to turn on when grounding the sensor wire to the engine. OP are you sure your coolant is flowing correctly? if the system has air in it maybe the sensors arent getting to temp in the same manner as your gauge sensor?
Silly question , but you did connect the water pump belt thats missing in your photo right?
Howdy, yes the belt is attached since that picture.
Hey all, sorry i had notifications off and had no idea there were any replies to this thread. I appreciate everyone's advice and wouldn't just ignore it.
On the ground question...i have this block grounded. There's a cable from the ear under the passenger head to the frame. I can stick a test light anywhere on the block and get continuity from the positive on the battery to the block, with the exception of the aluminum manifold and the steel water neck. I get no continuity there. I do get continuity off the bolts holding these 2 parts on. To be fair, there is paint on the outside of these parts, but the threads are not painted.
i did bring my senders in and tested them in boiling water. They both show continuity ( with the ohmmeter) at their respective temperatures (200 and 180 degrees) and once they cool off, i can hear the senders open back up and continuity fails back to open.
I'm not sure how you measure continuity between the positive battery terminal and the engine using an unpowered test probe, but I'll assume it's a terminology thing.
You say you have an ohmeter. How many ohms do you measure between the battery negative terminal and the engine block? How about between the engine block and the intake manifold? Between the intake manifold and the water neck? I can't image how these three items are not electrically connected, you will need to either scrape the paint away, or test to the body of the temp switch, which should be bare.
I'm not sure how you measure continuity between the positive battery terminal and the engine using an unpowered test probe, but I'll assume it's a terminology thing.
You say you have an ohmeter. How many ohms do you measure between the battery negative terminal and the engine block? How about between the engine block and the intake manifold? Between the intake manifold and the water neck? I can't image how these three items are not electrically connected, you will need to either scrape the paint away, or test to the body of the temp switch, which should be bare.
Let me test some more tonight and capture exactly what I am seeing.
Using my multimeter/ohm meter, all I've looked for is 1 or 0 to this point.
I'm not sure how you measure continuity between the positive battery terminal and the engine using an unpowered test probe, but I'll assume it's a terminology thing.
You say you have an ohmeter. How many ohms do you measure between the battery negative terminal and the engine block? How about between the engine block and the intake manifold? Between the intake manifold and the water neck? I can't image how these three items are not electrically connected, you will need to either scrape the paint away, or test to the body of the temp switch, which should be bare.
set the ohmmeter to 200 and tested the following :
Battery negative to block = .2 to .5
Battery negative to front sender body= .2
Battery negative to front sender terminal= open
Battery negative to gauge/cluster sender body= .2
Battery negative to gauge/cluster sender terminal= open
Battery negative to rear sender body= .2
Battery negative to rear sender terminal= open
(below measurements taken by removing sender and testing to inside threaded holes to avoid paint interference)
Battery negative to water neck= .2
Battery negative to rear intake hole = .2 to 16, depending on where i touch the thread
i guess I'm concerened about the difference on the measurements at the rear threaded hole in the manifold, but i cant get the front fan to come on and it seems to measure fine. I'd rather figure out the main culprit before i go chasing the smaller problem.
Electronical troubleshooting is not my forte, so i am stumped so far.
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