cooling fan

[DAVID GAGNARD]

Originally Posted by ironhead

Rick, thanks so much for your reply. Electrical is not my strong suit as you have guessed, but I will try to address each item you mentioned. My CR wiring might be a bit light at 14 ga from the fact. I had the 70 amp. alt. tested at Advance Auto, but they couldn't tell me what it put out, just that it works, which I knew. I have March pulleys, crank 6 1/4 in. Water pump 5 in. Alt. 3 in. Serpintine belt. MSD 6AL ign box. Optima 800cca 1000mca battery. My problems occur after the engine has warmed up and the fan kicks on the voltage drops from 12 1/2-13 down to 8 with only the fuel pump and fan on. A s you can imagine the car doesn't get driven much, 1500 mi. since completion in '90s. Thanks again Rick for your input.

For comparison on my 65 Mustang Fastback,I'm running the same size pulleys as you, I don't think the pulley size is your problem....I also run as full MSD ignition and a 19" diameter 2 speed electric fan off an early 2000 model Cadillac something or other I got at a local body shop.... I have it wired on high,never had the low speed even hooked up...Not sure of it's amp draw,but it is substantial.....along with all the other things electrical found a 65 Mustang (headlights/heater blower motor/windshield wipers/am/fm/cassette radio).....
I have the old style Ford 60 amp alternator,19.95 Auto Zone reman. special that is no less than 15 years old,I did convert it to one wire to eliminate the wiring and old style voltage regulator......Optima red top battery......

At idle with nothing on other than the car running,volt gauge reads between 13.5 and 14 volts,with the fan on volts drop to 12.5 to 13 at idle.....turn on the headlights and wipers and the volt gauge never goes below 12 volts and this is at 900 rpm idle......on the road volt gauge will be around 12.5 or a little better with everything on.....

Now back to the fan.....I have it wired with a heavy gauge wire from the alternator side of the starter solenoid and into a relay....when wiring anything with a draw like an electric fan, you need to use heavy gauge wires AND a relay..........

Your amp rating should be enough,I would drive it over to a dedicated alternator shop and have them check your amp draw with various things on and check the alternator amp output, that would tell you a lot more....your alternator could be putting out 13.5+ volts but with a bad or dead diode,your amp output would be less than the alternator is rated for......also they need to check your voltage regulator at the same time..........could easily be one or both causing your problem and being your volts drop to 8, I'm betting both!!!!!!!!

I think you'll find the problem in the wiring and the alternator amp output as a 70 amp alternator should be more than enough to keep up with the draw you have.....

David

[RICK LAKE]

Ironhead Was the battery tested and fully charged? I personally are not a fan of Optima batterys. Design is great for every where to mount it. Have had failures of them in higher vibration conditions. Lets test the battery with a full charge. If you have a head light and to wires, run the light of 60 seconds to take the top charge off the battery and test.
I can't under stand why they can't give you a full charging reading for the Alt. It could still be bad and breaking down once it warms up.
Wiring of the fans shoudl be in 12 gauge with heavy duty relays and using high speed only.
Is the heavy discharge happening at idle only? What is the idle on the motor?
If we raise it 100-200 rpms can the charging system handle the load? If yes, we may just need to get a smaller pulley on the Alt to increase thw speed of the Alt and keep everything charged. If not, and this was my car, I'm going to a 90+ amp Alt. Most cars and trucks on the street have over 100 amps now. The wiring is lighter in gauge because they removed the 10% fudge factor in safety of the trucks and cars. Saves money on copper which scraps for about $3.00 per pound.
Lets stay basic, check battery and test. After this we check rpm range with fans on and where the charging system can handle and charge all the normal loads on the system. Do this and come back with the answers and lets see wear this goes. My main concern is the AMP gauge, I have burnt off the insolators on this gauge with too much current going through it. I was running a 70A ALt with the orginal ALT from Ford. Over time the system could not handle the loads with being safe and almost cooked the dash and harness. You don't want to let the smoke out of any curcuit.
I will look at the March setup and see what the under and over drive ratios they have. I got a set of March pulleys for my FE motor and they where 20% underdrive and cause alot of problems.
Talk to you soon Rick L. Ps after we get this fixed we need to look at the curcuits for the fans and go to a larger wiring and 40 amp relays to protect the car over time.