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Fact or Fiction

I’ve been a do-it-myself mechanic since my first car at age 15. I always get people coming up while I’m fixing something giving me advice. Most all of there advice creates more problems. Like WD40 in the carb to clean things out, but deteriates the rubber parts. I wont go into all the advice I’ve been given here but get to the newest piece of advice.

In cold weather turn on your lights before trying to start your car. It will increase the cold cranking amps and start your car easier without running down your battery. Fact or Fiction?


As the current flow is warming up the battery plates it’s also draining the battery’s juice. That’s not something you want to do.

I’m sure glad I don’t listen to people coming up offering their advice anymore. Usually a few tools end up in their pocket. I sure hope I kept a good eye on him.

I also say fiction,I can’t see why diverting some of the batterys finite engery to the lights would increase the amount avialable to the starter.

There is a proven chemical property at work in regards to the battery being able to provide more “cranking power” when the battery is at a higher temp (it probably falls off as the battery gets to hot)

What is your theory (speaking to the OP)to either support or dismiss the question you have asked?

What is your theory (speaking to the OP)to either support or dismiss the question you have asked?

There may be something to it that may make it true but without further expert knowledge I’m still open to the possibility. It could be like tightening a bolt to brake it free before loosening it.

The theory behind this age-old myth is that the chemical reaction that takes place on the battery’s plates as it discharges creates enough heat to improve cranking power beyond that lost from the discharge.

Batteries have internal resistance so the more current you pull from them, the more their voltage drops. Turing off the lights reduces the overall current load therefore increases the voltage available to turn the starter. Therefore you should not turn on your lights until the car is running from an electrical perspective.

Everything you’ve stated is fiction.
WD-40 does not clean carburetors, it does not rot rubber parts, and the cold cranking amps things is really off base.

There are erroneous things posted on this board almsot every single day. Sometimes I argue the point; sometimes I don’t.

Fact On “Exciting” The Battery!

Except, the lights go on and then get turned off, and after a few moments the car is cranked.

CSA, my friend, are you suggesting that it works?

hmmmm, Could be. Come on all you experts. FACT or FICTION???


tsm, what are your expert creditials that will convience us you are right? Thanks


When you have a headache, do you put a knife under the bed in order to cut the pain in half?


Expert credientials: former avionics technician, former engineer.
Meaningful credientials: three years living in North Dakota.

But in truth, I’d love to hear the technical input of others on this. I can always be pursuaded by a good proper analytical explanation. I want to hear the “why” behind the opinions.

No personal attacks, you…you…you! Besides, it’s Holy Days.

By virtue of something being a theory, doesn’t even make it an accepted theory, much less proven fact.
Somebody has taken a factoid here, and a factoid there, and there, and joined them in an unholy alliance.
What will give you more cranking power is if you take the battery inside a few hours and let it warm. Then, re-install, and, without delay, start the vehicle.

Amen to that TSM. The “why” as to why it doesn’t work and the “why” as to why it works is always nice.

I tried the WD40 in a dodge 318 with a Holley carb that ran like a Top. One month later I had to replace the carb. he rubber was dried out and snapped like ice.

ok4450 explain your reasons why turning the lights on and off real quick won’t give the craning amps a boost.

It’s a cold winter across the country. It even snowed in Malibu last week. This is a perfect question to pose to the Mythbusters, Adam and Jamie. I’ll bet they will form an entire episode around cold weather car myths, and give them the scientific yea or nay treatment.

P.S. I’ve done it for you. Let’s see if they pick up on it.