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I fixed a parasitic drain on my car in 408 days

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Re: I fixed a parasitic drain on my car in 408 days

#121

Post by chrisdhal »

kccqzy wrote: post #7
overthrow wrote: post #3

Well this is timely. I have a parasitic draw on my NC Miata. The first mechanic just replaced the battery. The second told me it's normal for the battery to die if you don't drive it for 3 days (because "cars have computers now"). It seems like mechanics really don't like digging into the electrical part of the car... but these days that encompasses more and more of what can go wrong. Without time to dig into it myse…

> it's normal for the battery to die if you don't drive it for 3 days I've heard this nonsense a couple times now. I was incredulous at first but everyone seems to say this. What are anyone's suggestions for a weekend-only car? (I bike to work so I don't need a car on weekdays.) Trickle charge the car battery on weekdays?

My wife drives about once a week, probably less on average. She has a 2013 Honda CR-V, only 15,000 miles on it. We live in Minnesota, so have cold temps, but the car in a garage. The car always starts. We've replaced the battery once just due to longevity.

Every 3 days? No way.

Re: I fixed a parasitic drain on my car in 408 days

#122

Post by duskwuff »

peteradio wrote: post #115
duskwuff wrote: post #79

Earlier quoted context omitted.

> Yah, that doesn't really make sense for small parasitic loads. If your multimeter has a sub-mV range -- which a decent meter should -- you can measure a voltage drop across the battery ground lead. I've successfully done that to diagnose a battery draw in my car.

Exactly, you are measuring a change, so its the precision of the meter not the absolute V. Maybe easier to measure on a nearly dead battery?

I'm not talking about measuring the terminal voltage of the battery. What I mean is using the ground lead as a current shunt by connecting one meter lead to the negative battery terminal and the other to where the ground lead connects to the vehicle chassis. The voltage measured across that shunt is proportional to the amount of current being drawn from the battery.

It's the same principle as measuring the voltage across a fuse, except it ends up measuring the draw for the whole car, not just one circuit.

Re: I fixed a parasitic drain on my car in 408 days

#123

Post by jessaustin »

lylejantzi3rd wrote: post #96
cwillu wrote: post #63

Earlier quoted context omitted.

If you can identify the fuse for the unit, it might be less annoying to pull it when parking rather than hooking up a charger.

That's a great idea. I can't believe I didn't think of that. Thanks!

Pulling fuses is a pretty reliable way to find the relevant fuse in the first place. If the battery doesn't run down while a particular group of fuses is pulled, the one you want to pull is in that group. Start with half the fuses, then narrow down.

You might have to reprogram your radio channels...

Re: I fixed a parasitic drain on my car in 408 days

#124

Post by bronson »

ilyt wrote: post #109
Eumenes wrote: post #78

Earlier quoted context omitted.

I'm looking into buying a reliable older vehicle, pre 2000, and just rebuilding the engine

If car is at the point of engine rebuild you'd probably have to replace half of the suspension too

At least! When my engine finally needed a rebuild, so did the transmission, steering box, CV joints, and center differential. And you're right, it needed new bushings, shocks, springs, and balljoints.

Re: I fixed a parasitic drain on my car in 408 days

#125

Post by falcolas »

nuancebydefault wrote: post #99

Once you find the fuse that passes the highest current, why not just place a switch button in series with it? Turn it off when exiting the car. Add an LED to show when it is on.

Personally, I'd go for a relay on a non-problematic circuit.

But I also get why you might just leave it disconnected - if it's pulling a few more amps with no clear cause, what is going to go wrong with it next, and what vital system will it take with it?

Re: I fixed a parasitic drain on my car in 408 days

#126

Post by bityard »

overthrow wrote: post #3

Well this is timely. I have a parasitic draw on my NC Miata. The first mechanic just replaced the battery. The second told me it's normal for the battery to die if you don't drive it for 3 days (because "cars have computers now"). It seems like mechanics really don't like digging into the electrical part of the car... but these days that encompasses more and more of what can go wrong. Without time to dig into it myse…

> It seems like mechanics really don't like digging into the electrical part of the car.

That is certainly correct. Troubleshooting electrical issues takes a different set of skills than most mechanics are trained to deal with. Most mechanics are so busy that throwing parts at a problem is the best way to deal with issues where the cause isn't readily apparent. It's not worth their time to really dig into a difficult issue because if they spend 8 hours of shop time and try to bill that to a customer, the customer is going to just balk anyway. Better to throw a part at it, bill 1.5 hrs, send it out the door, and let the next guy deal with it. And then move on to some more profitable muffler and brake repair jobs.

This is thankfully not ALL mechanics, but it certainly is a large percentage of them, IMO. (Yep, even dealerships.)

Re: I fixed a parasitic drain on my car in 408 days

#127

Post by EricE »

ghaff wrote: post #46
tecleandor wrote: post #30

Earlier quoted context omitted.

Really nonsense. It's true it might be more common due to all the additional modules and computers cars have now. If one goes crazy, it might drain your battery. But this is only in case of a failure. Edit: cold weather can accelerate that. If it's 'weekend only', battery should be no problem. If sometimes you leave it a couple months unused, that might be a problem. Depending on how ready you would like to be when y…

I don't have extensive experience with my current car bought last summer but 2 weeks in warmer weather definitely wasn't an issue. I agree colder weather is always a bigger issue and at 1-2 months I'd definitely be thinking of a trickle charger if at all possible. An older car I didn't drive in the winter would definitely end up with a dead battery if I didn't keep it on a charger.

AGM batteries are a lot more durable than regular lead-acid. They can cost a bit more but for me the longer life, more resistances to issues if you do run them all the way down and their sealed, maintenance free nature makes them the first thing I swap out. Optima used to be the only commonly available batteries but Costco, for example, has AGM equivalents for just about every battery out there - you may have to order it and wait a few weeks.

They were also the original batteries used in Miata's since they give off a lot less hydrogen when charging. Since the Miata battery is in the trunk, and all lead acid batteries give off hydrogen when charging, and hydrogen in an enclosed space can also be rightfully called a bomb, having less of that is a good thing!

Re: I fixed a parasitic drain on my car in 408 days

#128

Post by dn3500 »

lylejantzi3rd wrote: post #96
cwillu wrote: post #63

Earlier quoted context omitted.

If you can identify the fuse for the unit, it might be less annoying to pull it when parking rather than hooking up a charger.

That's a great idea. I can't believe I didn't think of that. Thanks!

If it were me, I would pull the fuse, then jumper the block over to a different fuse on a circuit that is off when the ignition is off. Then you never have to think about it again.

Re: I fixed a parasitic drain on my car in 408 days

#129

Post by stuff4ben »

ksherlock wrote: post #60
overthrow wrote: post #5

Earlier quoted context omitted.

I thought about this but the problem with newer cars (mine at least) is killing the power wipes the memory so it won't pass an emissions check (or something like that). After my battery died I had to find an excuse to drive an extra 100 miles so I could pass emissions. On my car the emissions laws definitely caused more emissions than they saved that day.

I once had a car where I had to disconnect the battery to clear the check-engine light so it would pass a state inspection.

That usually doesn't work anymore as mechanics can tell that you've done that when hooking up the ODBII port.

Re: I fixed a parasitic drain on my car in 408 days

#130

Post by ssharp »

cwillu wrote: post #63
lylejantzi3rd wrote: post #28

Earlier quoted context omitted.

> It seems like mechanics really don't like digging into the electrical part of the car... Tell me about it. I'm in a similar boat. My audi a4 has had a parasitic draw for the past 10 years. My mechanic didn't want to take the time to address it because that sort of thing takes a serious amount of time and he's always backed up. I got out my fluke and narrowed the cause to what I believe is the comfort control unit.…

If you can identify the fuse for the unit, it might be less annoying to pull it when parking rather than hooking up a charger.

I wired in an aftermarket DVD player in an old car and tapped into a fuse that was supposed to not draw power when off. Of course, it did draw power so the DVD player never shut off. It wasn't too much of a draw but I didn't want to end up with a dead battery situation because of it so my solution was to just plug the fuse tap in when the kids were in the car and wanted to watch something.

I'm sure there was a more elegant solution (find a different fuse, rig up a button, etc.) but this was the path of least resistance and wasn't really annoying to do.

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