jamesld

I am trying to determine if a voltage drop is normal when the engine cooling fans are activated. The in-dash volt meter usually reads a needle's width shy of 14 volts under idle and normal running conditions. When the cooling fan activates, the volts drop to just a tick under 12 volts and at idle the engine shudders briefly while the volt meter needle slowly climbs back above the 12 volt mark. The fan turns easy by hand with no noticeable drag or bearing noise. I have cleaned all ground points. If other accessories are on at the same time as the cooling fan, the volt meter drops down further than with the fan only and continues to drop slowly from the 12 volt mark. I expect the meter to dip momentarily when the cooling fan comes on and then to return to the near 14 volt position almost immediately. Does this indicate a potential problem with the voltage regulator or the cooling fan control unit or is this normal? thanks for any feed back.

Randy V

A new car, James, or has it just started acting this way?

The general experience here is that any additional load (including the electric cooling fans) upon the charging system results in a downward deflection of the gauge.

While it could be symptomatic of a tired voltage regulator/alternator, unless you are experiencing some negative effects, I wouldn't worry about it.

MikeN

Not normal in my opinion. Sounds to me like you have a tired alternator or a battery about to go. The volt meter should show a very slight drop with both fans on, but not the amount you are talking about........and definitely should not make the car shudder at idle.

Would also be a good idea to go through the whole car checking grounds and connections.

jamesld

Randy,

Before I serviced the ground connections, the drop in voltage was more significant and the engine rpms would drop more sharply with a stutter or vibration in the engine at idle and with the other accessories on the volts were well below the 12 volt reading and would continue to slowly drop. I was just wondering if others notice a drop with fluctuations in the volts when the fans are running. It has been my experience with other systems that the volts tick back slightly when the fans come on, put rebound almost immediately to the previous reading while the fans are running.

A new battery or should I say the correct battery was installed a few months back. The PO had a Kmart blue light special or something else under sized that I noticed while I was investigating this issue.

Dennis Wilson

Before replacing anything, check the actual output at the alternator. The gauge voltage signal does not come directly from the alternator. Instead it is routed through the fuse panel and will often give false low readings especially if there are any corroded connections. On my 78 there are 7 connections between the battery and the gauge so it's common to see a drop when the cooling fan, heater fan, turn signals and brake lights are activiated.

Dennis

borland

Yes, those fans draw quite a bit of current. I notice a drop in the gage too, but only maybe 1/2-3/4 volts. The fan controller will operate one or both fans depending on temperature sensor conditions.

Because the alternator has limited current output at idle, I think it's normal for the fans to draw both from the alternator and from the battery.

On mine, when the fans come on, there is no engine vibration, but a noticeable fan roar.