trouble starting motor w/ elec. fan running

[bigvinnie]

Noticed over the past few months that starter was having problems overcoming the fan (thermostatically controlled)... For example, run into the store for something quick, come out, turn key on and fan starts, then try to start, and starter acts like the battery is low and just barely turns...

If I sit there with the key on and let the fan run til thermostat shuts it off, then try to start, works fine....

It used to start fine with the fan running, so I tested the alternator and battery and found that the battery was not taking a full charge... Replaced the battery with a new one, but it hasn't helped...

Wondering about the starter now... it's probably 10 years old and I was wondering if it could be demanding more power because of something worn, like brushes or contacts...???

Don't wanna replace the starter unless it makes sense...

thanks for any help...

[jef5150]

im kinda curious "WHY" your fan is hooked up to your ignition switch,,,,,,,the thermostat control switch should is supposed to determine when the fans turn on/off,,,,,,,"NOT" the ignition switch

[Class of 69]

I agree with jef...the thermostat wire should be direct wired with a fuse! The fact that the fan turns on when you get back in means it should have been running while you were in the store! The engine may be hot, and will affect the starters ability to turn it over. The starter is probably part of the equation also. The bushings that the armature turn in wear, and cause a bind, especially when hot. An old solenoid will affect how much amperage will get to the starter motor too. Starters aren't that hard to rebuild, just make sure you replace the bushings, as well as the brushes. To clean the commutator, I use 400-600 grit wet-or-dry sand paper, very lightly. Look for any broken or missing pieces of the insulators in the commutator...if insulators are bad, put it together, and trade it in on a rebuilt! If you rebuild it, be sure to replace the solenoid with a heavy duty one!

[ckenwright]

I believe most of your problem is you have the power wire for your fan circuit coming off the wrong lead on your ignition switch. When you put the key in the on position, the fan should run. Then during the period you turn the key to the start position the fan should turn off. And then turn back on when you release the key to the on position. The only thing that should have power is your ignition circuit. The fan should be part of the power on circuit.

If you need me to clarify what I am trying to say, let me know. I think this post might be a little confusing.

[jef5150]

Wiring

Red: Attach to positive (+) side of battery.
Orange: Attach to fan positive (+) lead.
Blue: When using dual fans, attach to second fan
positive (+) lead.
Yellow: Attach to an ignition switched 12-volt
source. If this wire is hooked up to a constant
source (like the battery) the fan will continue to
run after the vehicle is shut off and could run
down the battery.
Green: Attach to positive (+) wire on air
conditioning clutch. This runs fan whenever the
AC is on.
Black: Attach to a good chassis ground. Do the
same with the ground lead off the fan motor.

[jef5150]

http://www.derale.com/instructions/16759.html

[Longhorn Man]

There is no reason to wire a fan directly to the batt.
Compair an electric fan to the fan the truck origianlly came with. If the engine is not running, the fan is not on. Pereod. Also notice, no new car (with OEM electric fans) that I am aware of, is wired like that, they all turn on and off with the ignition (asuming the engine is hot enough to turn the fan on in the first place).
If you say the engione needs cooled so the fan should stay on...the fan is not cooling the engine...it is cooling the coolant in the rad. The engine should already have cooled coolant in it. Even if the engine IS overheated, cooling the coolant in the rad will do nothing for the engine since there is no water pump to put the coolant into the engine...the engine is off.
Always have the fan controlled with a thermostatic switch, and with the ignition switch. Less chance for fire, less chance for dead batery, and it will have no negitive effect on the cooling of your engine.


As for the original question, your fan is putting an electrical load on the system. If you were to test the voltsa and amps with the fan running, you'll see they are both lower than if the fan was not on. Your 10 year old starter is probably getting tired, and if you have headers, than this is just short of amazing that it lasted so long. (asuming full lenght headers, no heat shield, and a stock type starter)
The contacts in the starter arc every time you crank it, and in reality, melts just a little bit. After 10 years and one million starts, it is probably getting pretty crappy in there. Some people will take them apart and re-arange the contacts, but IMO (and that's all it is...my opinion) that is borrowing time. I would get a new starter, and if your fan stays on while cranking, (as ckenwright suspects) then rewire it so it is off while cranking.

[crazy4chevs]

a mini gear reduction starter would also help.

[bigvinnie]

Wow, thanks for all the replies... My explanation must not have been very clear, I think I was trying to be brief, and left out a few important details...... I'll try this again...

Once the motor is warmed up, the thermostat turns the fan on when it reaches 190... Let's say I shut the motor off while the fan happens to be on, then try to start it again... Turning the key to ON will start the fan because the thermostat told it to start.... it DOES NOT COME ON AUTOMATICALLY when the key is in the ON position unless the thermostat tells it to do so... then when I turn the key to START, it behaves as though the battery is low, and just barely turns...

I guess you all thought the fan was wired to be on whenever the key was in the ON position, it is not...

thermostat sits on the radiator fins, so turning the key to the ON position and letting the fan run with the engine off cools the radiator, and the thermostat shuts the fan off... then it starts with no problems.

ckenwright, you make an interesting point, I need to test whether or not the fan actually turns OFF when the key goes to the START position... I'm assuming that it does stay on by the way it's behaving, but I'll test it and find out for sure... and if it does, I'll need to wire it so it doesn't.... makes good sense, and thanks for the suggestion...

Either way, however, that doesn't explain why it worked fine this way before, and what you guys have told me comfirms my guess that an older starter/solenoid will create increased electrical load on the system....

By the way, I'm running stock rams w/ dual exhaust and I'm not having heat problems that I know of...

I'm gonna bet the worn starter/solenoid is the issue that is causing the problem in the short term, but having the fan and starter competing for juice is the big issue, and that's what I'll determine first...

I'll report my findings and let you know asap...

Thanks Again

[71GMC_3/4T]

Sounds to me like you could be drawing too much current through your ignition switch. What is the amp rating on the fan? 20A? That's a lot of current to run through your ignition switch contacts.
If you can wire it with a relay, you will be much better off.
It just doesn't make any sense that the fan would be hogging all the power though. The starter motor draws probably 300A, I'd guess (I don't have exact numbers), so that's a LOT compared to a fan motor. Check and clean your battery terminals and connections to the block and starter and the terminal block on the passenger fender.
When you say it won't start, does it roll real slow, or does it click? Clicking would mean that the solenoid isn't getting enough juice.
Try starting it with your headlights on. If the headlights dim significantly or go out, you have a supply problem like bad wires, a weak battery, or a shorted starter. If the headlights don't change much, you have a weak starter that can't draw enough current.
Good luck and let us know what you find to fix it!

[Class of 69]

Longhornmail...I beg to differ on the OEM electric fans. They all have a sticker on the fan shroud that warns the fan could start at any time, even with the key off! All the vehicles we've owned with electric fans come on after shutting them off when hot. I assumed the fan on bigvinnie's should also be that way. It should also shut off automatically after cooling to a preset temp, but does not appear to have that feature, hence the power from the switch. I agree, there is no circulation, but upon turning the motor over to start, the cooled liquid in the rad is circulated into the motor to cool it. All that said, it is still probably the starter. Bigvinnie, you can get the starter draw tested before pulling it out. I have a very simple meter I bought at a parts store that will test the draw also...cost about $15.00. You just hold it on the positive bat cable, while a helper turns it over.