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I have apparently destroyed my new cooling fan and need some help regarding wiring. Background: I just installed a new aluminum radiator, shroud, and electric fan into my 1957 3600 which is powered by a 350 engine with 700R4 transmission.
After a 30 minute test drive the cooling fan stopped running and of course the engine temp began to rise. To troubleshoot, I unplugged the fan connector and connected test leads directly to a 12 volt battery to verify the problem was actually the fan and not a temp sensor, relay, etc. I then connected a multimeter to the input side of the fan connector to check input voltage. The meter indicated 16.2 volts input to the fan. I assume this is what fried my fan motor. The fan installation directions indicated I should run a wire with fuse directly to the battery. Since my battery is underneath the truck bed and I wanted to avoid a very long lead to the battery, I elected to instead, connect the fan relay to the output pole of the one wire alternator (with a 30 amp cicuit breaker inline).

Is my problem caused by connecting directly to the alternator? Is my alternator output too high at 16.2 volts, thereby destroying the fan motor? Note: the in dash volt meter usually indicates from 12.2 up to 14.2 volts.

All help is appreciated, especially solutions that go beyond "remove the new fangled electric fan and install an engine driven fan".

Thanks

With the fan disconnected, use your meter to check the resistance of the motor at the fan connector.
Let us know what you read.

I6.2 V shouldn't burn out a 12 V fan.

Maybe the connection to ground failed during the test drive.

When you tested the fan, did you run 2 wires from the battery? (- to - and + to +)

Fix the charging system first, then worry about the fan, since you're choosing to ignore the right fix.
Jerry

Thanks for all the replies
buoy maker: If I measured resistance correctly, it is .01 ohms.
Gord; Yes, I connected the 2 test wires to the battery as you described.
Jerry: I plan to take the alternator to the repair shop Monday.

Question for all: Is it okay to connect the fan relay to the alternator as I have done instead of directly to the battery?

Thanks to all.....

Any wire connected to the battery (and anywhere along it, including at the alternator) will read battery voltage with the engine not running, and charging voltage with the engine running.

That assumes that the wires are the correct gauge for the current it's expected to carry.

So, yes, connecting the fan relay to the alternator should work just fine.

I don't know what fan size, cfm rating, etc you have, and I don't know what make. In my opinion Spal makes the best ones (Italy) followed very closely by Flex-A-Lite (USA). It should have around 30 ohms resistance (leads not connected to anything...just resistance across the fan motor). If the resistance is .01, that is basically an open circuit and tells me your fan motor may be gone. Good luck.

Rather than running a wire all the way to the battery, hook the positive lead to the plus terminal on the starter.

Ed

Open circuit is infinity (∞) or maximum resistance. 0.01 ohms (probably using a digital multimeter) would be a short.
You used a "30 amp circuit breaker inline" rather than a 30 amp fuse? If so, the breaker has a time delay to open to protect the circuit.
Unfortunately it can give more time for other parts to fail as well.
Usually the fan manufacturer provides a recommendation of fuse type and amperage rating.

It is and thanks for catching that...thinking backward this morning, I guess.

Jon I have mornings like that but they seem to happen more often as I get older.

Oldbolter. Go back to your troubleshooting steps after the problem occurred.
You unplugged the fan and checked voltage at the battery. What was the voltage?
Then you checked the voltage at the fan connector and read 16.2 volts. Was the engine running?

On a one wire alternator, I don't see a problem with connecting a fan circuit as long as it is properly fused.
Many use that point to supply headlight voltage via a relay contacts (shorter wires - less voltage drop).

Were you having any electrical problems before you installed the radiator and fan?

Exactly...the age thing! The sad thing is I've studied electronics on/off since late 1957. But the result remains bad for the fan motor...shouldn't be shorted nor open.

Jon: Yes, the fan motor is toast. It will turn even when connected directly to a battery. I have a new spare fan since the manufacturer mistakenly sent 2 and then said keep the spare since they didn't want to pay for return shipping. The radiator, shroud, fan, wiring harness and relay are all from Champion Cooling. The manufacturer recommended a 30 amp fuse. Instead of adding a fuse, I kept the 30 amp breaker from the previous fan install. I discussed the substitution with the manufacturer and they didn't think it would be a problem.

Buoymaker: At this point I"m not sure what the voltage at the battery was. I'll check Monday. Yes, the engine was running when I checked voltage at the fan connector. No apparent electrical problems before I installed the radiator and fan.

So, should I be using a fuse instead of a breaker?

Personally I would go with a fuse but I normally try to follow whatever the manufacturer recommends.

Since you have another new fan, check the resistance and post your reading. We can use that info to compare the two fans.

Sorry, I don't understand your statement, "Yes, the fan motor is toast. It will turn even when connected directly to a battery".

The new fan reads 4 ohms resistance and runs when connected directly to a 12 volt battery. So I am installing the new fan. The old "fan motor is toast" means the fan is dead and will not run no matter how it is connected.

Checked the battery and alternator output today:
Engine not running - Battery reads 12.6 volts. Alternator output terminal reads 12.5 volts.
Engine running - Battery reads 14.5 volts. Alternator output terminal reads 14.5 to 14.6 volts.
Engine running and 185 degree temperature - Fan connection terminal reads 14.5 volts.

Alternator appears to generating correct voltage at this time. Strange. So, I removed the alternator and delivered to repair shop to have a new voltage regulator installed.

"fan motor is toast" and motor will not run no matter, makes sense now. Thanks.

I was expecting a new fan to read more resistance. 4 ohms seemed low so I started reading about electric fans.
Now it gets complicated. Some fans have step resistance to vary motor speed. So 4 ohms is probably normal???
I have no idea without more information. Some fans have built-in control circuits and radiator temperature sensors.
I did a quick look at the Champion Cooling website but I wasn't able to find much information on their fans.

Back to the old fan. Just a thought. 0.01 ohms could have caused you regulator/rectifiers to overheat and voltage to go up.
For now I would definitely use a fuse for a quicker reaction to overcurrent rather than a circuit breaker.

Replacing the circuit breaker with a fuse sound like a good idea.

Thanks for all the help.