Radiator Fans Impacting Idle?

Hi, When the radiator/condenser fans kick into high, I feel like there is an extra 'load' on the engine and I can even see the RPM drop a bit where it sometimes stays or eventually kicks back up to the normal range. 1999. Car runs and idles fine otherwise. AC is good. Engine temperatures are perfect, etc. New water pump and thermostat, plugs, coil packs, etc, etc. I feel like the car has always done this and not the end of the world but curious if others have noticed the same. No other car I've had seems to act the same way when a fan kicks into high. Jeff

All normal. U have a cable throttle car and the iac sensor takes a split second to open up and bring the idle up. Most cars pre obd2 (1996) do this.

Thanks for the quick response! Glad to hear it is normal for the car.

Same observed on my 2000 (e-gas), easier to notice on the battery voltage gauge, basically just dips and rises over maybe 1 second.

When the engine is idling it is only producing about 5HP ( 3700 watts) ..when the fans kick on they can pull over 30amps (30A=360 watts) ( 360watts=.5hp) so you loose about 10% of your power when the fans kick on, then the DME has to increase power to compensate the idle speed..

The experts have weighed in on this, but I am curious what the voltmeter drops to when the fans kick on. The fans won't kick on unless the engine is warm and if the so called "Y" cable is corroded, when they kick on, the corrosion in the Y cable will also draw power putting an extra load on the alternator. If your voltage drops in the 12-13 range when the fans turn on, you probably have a Y cable issue exacerbating the fan load.

I'll drop into the 12-13 range when the high speed fans come up, all though the car is often already operating in the 13s during normal running, at first start its usually almost at 14. 2 years ago I had to deal with the slow crank warm start issue which ultimately needed the alternator to be replaced, my Y/ground strap is probably not in pristine condition but overall hasn't seemed to be a problem yet.

Based on the voltage drop, your Y cable is on its way out. At some point, when the fans turn on, it will hit 12v at which point you should make plans to replace it. When battery and alternator and cable are working as they should, the voltage should not drop below ~13.5V. I know this from experience with these cars and I am an electrical engineer. The Y cable is insufficiently water proofed at the Y point, water gets in and it corrodes. That creates a high resistance point that should not be in the charging circuit and limits to charging voltage to the battery leading to failure.

Yea, after typing it out yesterday I plugged back in a monitor to the cigarette lighter to get a numeric reading from there when driving, which indicates I'm down to 13 volts flat once everything is warmed up. I've got an icarsoft scanner which had a reading purporting to be battery voltage and was pretty consistently showing 13.6-13.8 when the car is running, so I'm assuming its pulling that actually from the battery while the interior will be from a circuit impacted by the y cable, don't have a diagram in front of me. I've got a 4 year old H7 AGM battery which is still holding up and did fine this winter, but I think I'll move y cable/ground strap onto the service soon list.

dsbl, The Y cable is a combo of two wires joined together to make it a Y. One cable (let's call it "A") runs from the alternator to the starter, while the other (call it "B") runs from the starter to the + jump point to the right of the power steering. From there, a different cable runs up to the battery. While the single point ends of A and B are sealed from the elements, where A&B meet, they are inserted into a zinc or similar metal lug and a press crimps the two wires together. There is no weather proofing around that connection and so, unless your car never sees high humidity or wet weather, eventually the galvanic reaction of the dissimilar metals will corrode the connection and create resistance to the flow of current. Current passing through a resistor draws voltage form the circuit and is why the volt meter drops as the engine heats up. The more resistance, the hotter it gets and you see the volt meter drop until at some point it drops to ~12v at which point your battery is no longer being charged.

Thanks for the pic and explanation. I put the ~14V right after engine start that then steadily reduces to just under 13V to the battery being charged back to the energy level it had just prior to starting the engine. I.e. it is expected behaviour. I'm curious to hear what those who have replaced the Y-cable observe in this case. Anyone who did, care to share?

Quotes source post: 19455810

I replaced battery, alternator and Y cable (I did not need a battery or alternator, the Y cable was the issue, but bad tech gave advice). With it all working as new, voltmeter on dash reads just above 14V on start and when warm with fans running it drops below 14 but never gets as low as 13.5V.