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Discussion Starter #1
I have a Spal electric fan on the 70 stang that apparently pulls quite a few amps as the fuse on the main power wire is a 30 amp fuse and the wire is either 8 or 10 gauge. After I shut off the car, the fan continues to run until the temp. sensor tells it to shut off, which is ok. The difficulty is that if I try to re-start the car when the fan is on, there is barely enough amperage to turn over the starter. The other day, I could not even get the solenoid to click over when the fun was running. After trying a couple of time, the battery cable was hot to the touch. I have an Optima battery, about 2.5 years old. My questions are:

1) how many amps does it take to turn over a starter on a small block in 104 degree heat?

2) Do I need to upgrade my battery to something with more cranking amps?

3) should I install a fan cut off swith inside the car and just manually turn the fan off when starting the car, then turn the fan back on once the car is running?

fortunately, I have a 110 amp alternator so once the car is running, there is no problem.

My battery is in the trunk and I am using No. 2 welding cable for battery cable. I am pulling power for the fan from the Moroso battery on/off switch which is wired into the battery cable,under the passenger fender and just before it connects to the starter solenoid.

Any suggestions? Trying to start the car with the fan running drains the battery very quickly.
 

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Most electric fans pull a LOT of amps ... thus the need for high amperage alternators to run them. I'd say your best 2 options are a manual shut off switch, or use a relay on it (or move the power to the relay if you're curently using one). If you wanted the fan to still run afterwards, you could power the relay from the radio circuit or similar (using an existing plug in the main harness). That way, when the key is turned to "start", power to the relay is cut, which would cut the power to the fan until the key came back out of "start".

Now, I won't guarantee this to work. I changed my electric fan to not run after the engine was off, because it just pulled too much current. It left me stranded twice with a dead battery, and I said enough is enough. Wired the relay so that it's on a switched ciruit that only gets power when the key is in the "on" position.
 

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I'm running an Aussie,"Davies Craig" fan,through a relay & adjustable thermostat.It only comes on at a preset temperature & generally only at idle in traffic.
They certainly suck the juice.....it drops the idle a little when it kicks in!
Is there any advantage running the fan after the engine is shut down?Seems to me it would only be cooling the water in the radiator.
Greg
 

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You are correct, in that all is does is cool the water in radiator. It does help, though, when you go start the car back up, especially here where the temps often get over 100 degrees. You can start it back up and immediately have cool water running back through the engine, instead of the water that sits and heats up even hotter once the fan/engine is off. The trade off, though, is a weakened battery to start it back up with.
 

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How is your starter?

You described a classic example of a heat soaked "dragging" starter. I would think if the battery still had 12.5V after the fan shut off, you should have enough reserve in the battery to start the car.... Unless the fan is running for an unnecessarily long time after the engine is stopped.
 

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I wired my Spal Fan in with a a relay that cuts the power to the fan when I turn the car off. My thoughts were that if that high amp fan is running while the engine is off, its sucking the juice out of my battery, and would eventually kill it, like Jonhpro stated. I would consider an ungrade to a bit higher amp alternator if your running a stock one, and i'm not sure where you live, but 2 1/2 years for a car battery out here in Arizona is a long stretch, not sure about the Optima batteries, they probably last longer, but I noticed a big difference in starting when I finally changed my battery out, its been a year now and still starting strong, might want to get your battery checked out. Good Luck. james.
 

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What kinda shape are your battery cables in and are the terminations at the block and starter clean? If they are not clean or there is some other reason for resistance, you will experience the symptoms you described.
 

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Discussion Starter #8
The battery terminals are in great shape. I went back and recleaned them anyway with 320 sandpaper, and also the terminal ends. I traced the cable up to the switch and cleaned the switch terminals also. The one thing I have not cleaned is the starter connections. It is possible, I suppose, that paint overspray has gotton on there and is creating some resistence. I'll check on that. Thanks.
 

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Discussion Starter #9
hmmmm. The spal system includes a relay which is powered directly from the battery cable (in my instance), protected by a 30 amp fuse. There is a much much smaller wire pulling way fewer amps that activates the fan motor once the relay is tripped. Your fan comes on only with keyed power if you source the power for that wire from a keyed source. I'll try JohnPro's idea and move that wire to the radio power lead (since I don't have a radio) which means the fan will cut off when the starter is engaged. Thanks for the input,
 

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Discussion Starter #10
What is a "heat soaked" dragging starter and how do you fix it? I've never heard of that one before. Thanks.
 

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Discussion Starter #11
Well Greg, I am not sure of the advantage of running the fan with the engine off. I was only imitating what some production cars have. Have you ever walked down the row of parked cars at the local market and heard a car fan running, with the engine off? That is what motivated me to wire it the way I did. I guess if the car had a mechanical fan it would not be "running" with the engine off so it can't be too bad for the car to not have a fan rotating when the engine is off. I am going to wire it differently today and see if that helps.
 

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Discussion Starter #12
I have a relay in the system, which I've powered from the battery on off switch. There is a different power wire that determines whether the fan trips with keyed power or constant power. The sourcing of that wire is the key (pun intended). I will move that to the radio cirucit and see if that helps. Thanks for the input. Amazing how there is such a vast difference between winter and summer car performance!
 

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Ahhh, thats it, I remember now, your right, that grey wire that leads down to the water temp. sensor for the fan, is the one I added the relay to, not the power wire to the fan.
 

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What is a "heat soaked" dragging starter

Engine cranks fine when cold (cool) but slow when warm... Heat from the motor increases electrical resistance inside the starter and requires more amps to spin the engine.

I suggest a load test on the battery to determine it's condition first, then disconnect the fan after you've stopped and see if the problem clears up...

Normal starter shouldn't pull over 160 amps and the voltage drop should be less than a volt with a warm engine.
 
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To answer one of your questions...a typical small block will require somewhere in the area of 100+ amps while cranking.
Add 50% more to the mix if you have high compression and/or advanced timing and excessive heat. So, alot is being asked of the starting system, let alone having the extra drain of the fan.
However, with #2 ga. wire, which has about 150 milliohm(0.150 ohm) per 1000 ft, your run from the trunk shouldnt be an issue. What does seem to be an issue is one of your connections.

VictorII is on the right trail. Your problem is a high resistance connection from the battery to the starter, perhaps even a high resistance in the internals of the battery itself.
It may not be enough to simple clean the terminals. I have experienced bad connections inside the head of the battery terminals where the wire cable is internally connected to the lead casing. You mentioned that the cable is hot. Thats actually not a bad way of finding the problem area. Next time this happens, feel each battery terminal for heat. If it feels toasty to the touch, you have a bad connection right there and as mentioned earlier, it might be hidden in the connector itself. Now, SOME heat is expected, but it shouldnt be so hot you can't keep your fingers on it, especially being located in the trunk.
An even better method involves using a voltmeter. If you have one, monitor the voltage directly on the battery POSTS while cranking the starter. Then measure the voltage at the cable terminals. There should not be more than approx. 0.1 volt difference. Otherwise there are bad cable connection(s). If the battery voltage at the posts drops below 10v, then your battery is suspect. Time for a newer, higher amperage model. I have focused on the battery but it may also be a bum connection at the starter/solenoid or the chassis ground on either end.

Finally, if all this looks ok, dont overlook Arts suggestion of the starter. A starter that is "tired" and hot with diminished bearings will draw much more than normal current. In that case it would be time for a rebuilt.
Will stop the rambling for now. PM me if you would like more detail.
 

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Discussion Starter #16
Thank you very much for this very informative post. I only cleaned the positive wire connections. I will go back now and clean the negative connections as well as the connections on the solenoid to starter wire. I paint I have paint overspray on that one which could be messing things up a bit. My volt meter is one of those which thinks fine measurement is being within 5 volts of the true voltage. haha. I'll borrow a better one to check the battery with the methodology you describe. Started pretty good this evening, even with the fan on, but then again it was not 100 degree plus out. Thanks for the info.
 

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If the battery voltage at the posts drops below 10v, then your battery is suspect.

Is this while cranking?
You could also get a low voltage reading from the battery if the starter is pulling all the power from the battery.

The only real way to test a battery is perform a load test when the battery is fully charged (a free service done at most chain auto parts stores)...
 
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Good point, Art. I did mean while cranking. However, rethinking the issue, a good battery may drop below well below the 10v level while cranking. Thats why there is a ballast resistor in series with the ignition coil because the coil has to work at a diminished voltage during starting then at the full 12 to 14volts after starting. The ballast resistor is bypassed during starting.

In any case, as you suggested, a good battery shop should be able to determine the health of the battery. Even if the battery condition should be within manufaturers specs, it still may not be well suited to this application especially given the extreme conditions of load and heat.
 
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