cooling fan

[RICK LAKE]

iron head 3 problems, Lets start with charging system, How big is the Alt in amps? How many curcuits are pulling power when the car is running? Lights, electric fuel pump,Ignition box, ECU for FI system? If this happens at idle the Alt can't keep up with the load on the system. I am going to say that the battery is new and fully charged. It doesn't hurt to pull it and go and have it tested for loads and CCA rating. You could have a bad cell. Car will start and run but with things on like cooling fans they pull about 10-20 amps. At idle the charging system can't charge the battery. Ideas charging for a battery in voltage is 13.7-14.2 volts. As long as you are 12.7 volts and holding with all drains on you are ok. Anything less need to rework the system, see below.
3 possible fixes
1 Does your motor have March pulleys on it and are they underdriven? If YES need to go. The Alt is not spinning fast enough to keep both the battery and load getting enough ampage to system. The water pump and crankshaft pulley should be the same diameter. As for the ATL pulley size should have the stock pulley on it for a loaded opitioned truck or car. If not change pulleys first. If you have alot of curcuits running at idle, the battery will discharge trying to keep power going to every curcuit.
2 Output of Alt, in the old days we had only a couple of curcuits in a cobra. 37-42amp Alt was fine for this car. Today, multi fans, electrical fuel pumps, Ignition boxes, Better head lights, Stereos, and other power drainers. Need a higher power Alt in the 90+ ampage for the car to start everything and handle all the loads at idle. There should be a number on the ALT that said --amps. We are looking for 80 or higher. The Alt can be pulled and tested for output also. One of the diodes could be burnt out and cause a weak output on the ALT. OUtput should be within 5% of number on case. Less buy a new rebuilt Alt. There is a PROBLEM with running more than 70 amp ALT's. The Amp meter in the dash Can't handle this load over long periods of time. There are other threads about amp meters burning up dash harnesses, melting the insolators on the gauge and other problems. IF you are going with a higher output Alt than 60 amps, replace the Amp gauge with a voltage gauge. Works almost the same and you can chack the output of the charging system looking at the gauge. A simple rewiring from amp to volt is done. Will need to add a 125 fusible link to the output on the Alt for protection of the car incase of a short or rub through on the power side.
3 There could be something going bad with the coolant fan(s). Need to find out how much ampage they are drawing. When the fans kick on there is a ampage and voltage drop for a second. The gauge could pin and bounce back with them running. Other thing is a bad relay for the fans. These are easy to replace and might help lessen the spike load.
The bad thing with a cobra having a amp gauge all the loads go through it. There are only 2 terminal post and small nuts that handle this load. under 60 amps total no problems, over 60 amps, looking for a melt down over time. Either way replace this gauge. This should give you all the info you need to fix the charging system.
A place called PA preformance sells a complete kit to swap out to a bigger Alt leaves the voltage box and looks orginial in the car. This kit works great. I have it on my car as well as going to a voltage gauge. Good luck with problem. I think you will fix it. Rick L.

[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.

[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.