Electric fan and RPM issues

[66FSTBCK]

Originally Posted by zstang

2 things, 1 if your using the stock style starter solenoid, make sure it's grounded good. and 2, additional ground strap/cable doesn't hurt. i run a cable from the batt. to the chassis and 2 different cables from the chassis to the block. good luck

I currently have one from battery to block and block to firewall.

[Shocky]

Sorry to disagree with everyone, but corrosion will cause a high resistance, decrease current and instead of dragging down the engine it should have even less effect. It sounds more like a grounded positive lead, motor, relay or God knows what. If it won't do it on command you'll have to try to help it along. Wiggle the wires while the fan is running. Tap on the relay with a screwdriver handle. Feel free to smack on every part of the system, including the alternator. Unfortunately, having been a steel mill electrician for 30+ years I know first hand that sometimes all you can do is wait these problems out. By the way, the fan is fused or on a breaker, right?

[ivancaicedo237]

Originally Posted by 66FSTBCK

Lately when my e fan kicks on it pulls my rpms down to where the car nearly dies. Then they will begin to be erratic. I can see my volt gauge drop too when the rpms begin to vary. No problems when cruising. Fan is hooked in with a relay and I am using a one wire 100 amp alt. problem just started recently. I checked the grounds and everything looks good. Bad relay possibly??

The fan draws 13.5 when its running normally, on start up its about 6 to 9 times more for that brief second. Its called motor inrush. Either the fan is starting to go, or the battery is not holding up to the spikes anymore. I got a 140 amp alternator and everytime it starts the alternator assumes load and tries to stall the engine via the belt. The stronger the load the more it tries to lock up the alternator. I am guessing its getting colder in your area so perhaps to cold weather is lowering the cranking amps on the battery. If you got a solid battery, the alternator will stop stalling at whatever the battery voltage is. The load cannot bring both the alternator and battery together. Well it can but it gets harder. I guess what I am trying to say is weak battery = load goes to the engine, strong battery= load goes to the battery. Half good batter,half good alternator = both take the hit.

[66FSTBCK]

Just got back from Autozone and the battery and alternator tested perfect. I bought a new relay while I was there and will check the grounds and relay tomorrow.

[ivancaicedo237]

Originally Posted by 66FSTBCK

Just got back from Autozone and the battery and alternator tested perfect. I bought a new relay while I was there and will check the grounds and relay tomorrow.

Awesome, if your meter has a min max mode, see what the voltage drops to on the battery and compare it to the motor when the fan kicks on. I dont think you should see a difference more than half to a full volt. It all depends on the wire you used.

[66FSTBCK]

Originally Posted by ivancaicedo237

Awesome, if your meter has a min max mode, see what the voltage drops to on the battery and compare it to the motor when the fan kicks on. I dont think you should see a difference more than half to a full volt. It all depends on the wire you used.

Is this what you mean? From the first page:

-Battery tested at 12.75v with car off
-Car running w/o fan on 14.95v
-Car Running w/ fan on 14.87v
-Car running w/ fan and headlights on 14.00v
-Battery tested at 13.33v w/ car off after running

[1koolride]

was the battery load tested or just tested for voltage? sounds like either battery not up to par on the load test or a bad relay. Also might try tapping on the fan motor while it is running to see if it speeds up or slows down,if it does either then you have just found the problem.

[66FSTBCK]

According to another poster on this thread, they put a load on it when they test it. My results were with just what was listed above.

[ivancaicedo237]

Originally Posted by 66FSTBCK

Is this what you mean? From the first page:

-Battery tested at 12.75v with car off
-Car running w/o fan on 14.95v
-Car Running w/ fan on 14.87v
-Car running w/ fan and headlights on 14.00v
-Battery tested at 13.33v w/ car off after running

Not really, Sometimes there is a button thats says min/max. What it does for instance if you place it on min, you put your meter on the battery, go inside the and crank the engine over. The meter will capture the lowest reading and hold it. Same for max. If you place it on the max mode. Place the meter on the battery. Start the car and shut it down. The meter should capture the maximum voltage seen and display that until something higher comes.
Its pretty awesome for knowing if your battery is going to shart on you. While cranking, your starter is like the mega load on the car. It draws about 4 to 6 hundred amps. While cranking you dont want to see the battery dip below 9 or 9.5. Same if the fan kicks on. You dont want to see a dip below 12.

[bartl]

Disconnect the wire from the - side of the coil and check voltage at the + side while jumping the coolant temp sensor to engage the fan. Note the voltage. Where are you picking up the power to your Pertronix?

Step#2- Hang a timing light on the coil wire and check out the pattern when the fan comes on. It should remain a regular flash-flash-flash that varies with engine speed. If it looks like you're starting to lose spark intermittently then you've narrowed the problem down a bit.

[66FSTBCK]

I checked the grounds and replaced the relay....no change. I put the old relay back in and let the engine get hot again so the fan would turn on. At this point it was idling about 600-700 rpm so I bumped it up to 800-900 and it ran perfect. No fluctuation in rpms or anything. I wonder if the engine is starving for fuel?? Is this where the idle mixture screws can come into play??

[65ACodeCoupe]

Originally Posted by 66FSTBCK

I checked the grounds and replaced the relay....no change. I put the old relay back in and let the engine get hot again so the fan would turn on. At this point it was idling about 600-700 rpm so I bumped it up to 800-900 and it ran perfect. No fluctuation in rpms or anything. I wonder if the engine is starving for fuel?? Is this where the idle mixture screws can come into play??

The alternator is not putting out enough at 600-700 rpm to sustain both the fan and ignition requirements. It may be a 100 amp alternator but that is maximum output at much higher rpm than idle. The output is a lot lower at 600-700 rpm. At the higher rpm ( 800-900 rpm ) it seems to be meeting the electrical demand. You can set your idle at 800-900 rpm, or you can run a smaller diameter alternator pulley (if available), or you can change to a much higher output alternator e.g. 150A that will have more output at idle.

I run a 150A alternator. With the heater blower on full blast, wipers running on high, lights on bright, and electric fan on there is no fluctuation in the 850 rpm idle.

[66FSTBCK]

Originally Posted by 65ACodeCoupe

The alternator is not putting out enough at 600-700 rpm to sustain both the fan and ignition requirements. It may be a 100 amp alternator but that is maximum output at much higher rpm than idle. The output is a lot lower at 600-700 rpm. At the higher rpm ( 800-900 rpm ) it seems to be meeting the electrical demand. You can set your idle at 800-900 rpm, or you can run a smaller diameter alternator pulley (if available), or you can change to a much higher output alternator e.g. 150A that will have more output at idle.

I run a 150A alternator. With the heater blower on full blast, wipers running on high, lights on bright, and electric fan on there is no fluctuation in the 850 rpm idle.

Great information, thank you! I guess we found the problem! I'm not sure why the problem started all of a sudden, but I had been tinkering with the idle screw so it could have been around the same time . I am not a big fan of the higher idle, but if it eliminates this problem then I will keep it there OR buy a bigger alternator.

[bartl]

A couple more options would be to slightly decrease the size of the alternator pulley or have an alternator shop see if they can tweak the alternator to produce more output at a lower rpm.