Is it normal for dash lights to dim and blower fan to slow down when idling at a stop light?

Posted by Blu_yello_husky@reddit | askcarguys | View on Reddit | 10 comments

The reason I'm not listing a make/model here is because this is universally true across 3 different cars from 3 different companies and 3 different years, so it cant be a 1 car specific thing. This is a general question. I've been noticing that on 3 of my 4 cars, when I come to a stop at night with the blower on high speed and the headlights on, the dash lights dim so low you can barely see them and the fan speed slows down noticeably. The turn signals also slow down but I already know thats a normal phenomenon on cars. As soon as I rev up to accelerate from the stop, the fan comes back to life and all the lights brighten again until the next stop. During this time, the amperes gauge is still between 13 and 16 on the dial, and to further rule out alternator, 2 of these cars have recently had the alternator serviced and 1 has a newer battery. The battery guage on all 3 cars stays in the normal range the entire time during stops and acceleration. Im just wondering if this is a normal, expected phenomenon, like the signals slowing down, that i just somehow never noticed before, or if this is caused by an underlying issue i may need to address in the future. Thanks in advance

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10 Comments

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fishin413@reddit

It seems so ridiculous that you wouldn't just state in the post you're talking about three 40 - 50 year old shitboxes like thats not important information. Regardless, no, that is not normal for any car and a properly functioning alternator and charging system produces more than enough power to run headlights and fans and dash lights at idle.

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Blu_yello_husky@reddit (OP)

Because ultimately its a general question so it shouldn't matter what the cars are, and outside of that, in my experience, if I put right away in the post that im talking about older vehicles, I get little to no responses because people see old and somehow forget how to answer a basic question. Electricity operates the same way today as it did in the 70s dude, its not like the laws of physics changed when computers started getting put in cars. >Regardless, no, that is not normal for any car and a properly functioning alternator and charging system produces more than enough power to run headlights and fans and dash lights at idle. Interesting. Your answer conflicts with others in the comments already.

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fishin413@reddit

> I get little to no responses because people see old and somehow forget how to answer a basic question. Electricity operates the same way today as it did in the 70s dude, its not like the laws of physics changed when computers started getting put in cars. I wonder if you get no responses because you're kind of a twat. The dash didnt shut off at red lights when they were brand new, so its normal now either especially considering "electricity operates the same way today", dude. > Interesting. Your answer conflicts with others in the comments already. No it doesn't, thats why all 2 of the other comments include caveats like "if its super noticeable" and recommendations on how to fix it. A slight, temporary voltage drop is normal, it is not normal for voltage to drop to the point that your dash lights go out and your blinkers slow down. That would be considered "super obvious".

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Blu_yello_husky@reddit (OP)

>The dash didn't shut off at red lights when they were brand new They might have, I don't know, thats what im asking. Good lord your comprehension is terrible. >dash lights go out They don't go out, they go dim enough that you can hardly see them without squinting. >your blinkers slow down. This IS normal, and all cars do it. I wasn't concerned about that. I know thats how blinkers work, and yes, they DID do that brand new too. It's just the way turn signals work on older cars. As engine rpms slow down, so do the turn signals. The engine speeds up, so do your signals. And it's been that way on EVERY SINGLE CAR ive owned. That's 16 cars over the last decade or so years ranging 1970-1990. If you think that's not normal, then clearly you aren't fit to answer my question to begin with

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fishin413@reddit

😂

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FlyingWhale44@reddit

It does kind of matter though. On newer cars, auto start/stop can affect the fans blowing, and a lot of people don't know that, or don't even know if they have that feature on their car in the first place, let alone tell if it's on or off. Some cars are known to have certain issues, others are not. Sometimes that affects certain years specifically. Anyways, it wouldn't take you more than a few seconds to just list the cars affected and it would help people who are trying to help you.

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Tape_Face42@reddit

What cars?

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Blu_yello_husky@reddit (OP)

78 chrylser cordoba, 74 mercury monterey, 83 oldsmobile 98.

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Otherwise-Ad6675@reddit

Yeah that's normal on that era of cars my 89 dodge does the same thing although if it is super noticable check belt tension and maybe bump up the curb idle if on a carbureted engine.

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Cheap-Chapter-5920@reddit

Sounds like voltage drooping, which maybe normal depending on the car. Idle speed might be too low, alternator pulley might be too large for idle speed. I've had this with older cars but modern cars are a lot more regulated voltage.