Auto repair myths

[spidey07]

Originally posted by: ironwing
Okay then, what is your explanation for generations of experience that shows that if you warm the car up before putting the car in gear it won't die while if you just start it up and try to drive off, bang, dead, now need a jump? Ambient temperatures from -30F to +10F. Keep in mind that this experience is mostly, but not completely, with carburated engines not fuel injected.

Cold motor or faulty alternator.

 

[PlatinumGold]

Originally posted by: ironwing

Originally posted by: Zenmervolt

Originally posted by: ElFenix

Originally posted by: Zenmervolt

Originally posted by: WhoBeDaPlaya

Originally posted by: ironwing
But most people who warm their cars up aren't doing it for the benefit of the engine. They do it mainly because they want the heater to warm up the cabin. Also, they are trying to charge the battery so the car doesn't die when put in gear.

I thought that idling doesn't really do much for the battery. Don't you have to rev it somewhat to do any good?
Disclaimer : Car n00b here

Depends.

Motorcycles: Most won't charge the battery at idle.

Cars: Almost all will.

However, the idea that one has to let the car idle to "charge up the battery" so that it doesn't "die when put in gear" is, quite frankly, stupid. An alternator puts out more than sufficient charge to keep the car running, and if the battery has enough juice to start the car, it's not bad enough to cause the car to stall. (A battery that is shorted internally can suck enough juice to cause an engine to stall, but such a battery wouldn't start the car in the first place, and even if the car were jumpped, it wouldn't idle.)

ZV

i had a dead battery that, after the car was jumped and idling on its own, was so bad that when i put it in gear it died.

Absolutely no way it was the battery. The alternator, even at idle, puts out sufficient energy to run the engine even if the battery were removed from the car. Unless the alternator is defective as well.

Under no circumstances should a running automotive engine be dependant on the battery to remain running.

ZV

Okay then, what is your explanation for generations of experience that shows that if you warm the car up before putting the car in gear it won't die while if you just start it up and try to drive off, bang, dead, now need a jump? Ambient temperatures from -30F to +10F. Keep in mind that this experience is mostly, but not completely, with carburated engines not fuel injected.

mb your alternator is not putting out enough juice, MB that's why your battery was dead in the first place.

 

[gsellis]

Originally posted by: daveymark
smoking while pumping gas is dangerous

Mixed. Not a myth. I have seen the videos of the fires start with a cigarette, but the ATF tested for an arson case that showed it did not. I suspect it is a combination of temp and if a butt sparks on the ground.

On the car running, not really today, but I know some modded cars that you would not want to be around (mostly rotaries). Had an RX-3 start the grass on fire at Turn 11 at Road Atlanta after a spin from visible flames out the exhaust.

 

[cubby1223]

Originally posted by: ironwing
But most people who warm their cars up aren't doing it for the benefit of the engine. They do it mainly because they want the heater to warm up the cabin. Also, they are trying to charge the battery so the car doesn't die when put in gear.

Heh. I never let my vehicle's engine warm up before starting off. Maybe 30 seconds at the most. Usually in the winter, I'll start up the vehicle, then however long it takes me to get all the snow & ice off the windows, that's how long it gets to warm up before I go. Some people have their cars running 15-20 minutes before heading off. I just see that as a waste of gasoline (i.e. money), and I just can't do that.

Funny, after my brother once had his battery go dead & got a jump to get home from work, and once home leaves the car running to recharge the battery. Well, forgets about it, about an hour later finds out the water pump has broken, coolant leaked all over the driveway, and the engine's overheating. That was a costly mistake leaving it running unattended.

 

[Pacfanweb]

Originally posted by: Zenmervolt

Originally posted by: ElFenix

Originally posted by: Zenmervolt

Originally posted by: WhoBeDaPlaya

Originally posted by: ironwing
But most people who warm their cars up aren't doing it for the benefit of the engine. They do it mainly because they want the heater to warm up the cabin. Also, they are trying to charge the battery so the car doesn't die when put in gear.

I thought that idling doesn't really do much for the battery. Don't you have to rev it somewhat to do any good?
Disclaimer : Car n00b here

Depends.

Motorcycles: Most won't charge the battery at idle.

Cars: Almost all will.

However, the idea that one has to let the car idle to "charge up the battery" so that it doesn't "die when put in gear" is, quite frankly, stupid. An alternator puts out more than sufficient charge to keep the car running, and if the battery has enough juice to start the car, it's not bad enough to cause the car to stall. (A battery that is shorted internally can suck enough juice to cause an engine to stall, but such a battery wouldn't start the car in the first place, and even if the car were jumpped, it wouldn't idle.)

ZV

i had a dead battery that, after the car was jumped and idling on its own, was so bad that when i put it in gear it died.

Absolutely no way it was the battery. The alternator, even at idle, puts out sufficient energy to run the engine even if the battery were removed from the car. Unless the alternator is defective as well.

Under no circumstances should a running automotive engine be dependant on the battery to remain running.

ZV

I'll tell you what I bet happened here: ZV, you're right that the car runs off the alternator. The battery is only there for starting purposes.
But since this guy's battery was dead in the first place, what happened was, the ECU had forgotten all it had learned about the idle strategy of the car. So when the battery went dead, it reset to its default....which, if you've ever changed batteries on a car with some miles on it, will make them not idle correctly until it re-learns how to idle again. So you'll get stalling, idling up and down, etc.
So he had a dead battery, jumped it and the alternator was fine to keep the engine running, but the idle was messed up, so it stalled, and he still had a dead battery.

I've seen this many times....people would come in for a dead battery, then when we fixed it, it would have an idle problem. Of course they'd think we did something to the car, and say "it idled fine before".
A throttle body clean usually fixes this concern.

 

[91TTZ]

Originally posted by: Zenmervolt

Originally posted by: RGUN
WHAT?? So you're driving along an icy road and you need to slow down, apply brakes and use all the wheels and the ABS safety net OR downshift to a lower gear therefore making power application much less smooth and risk locking the wheels? yeah thats intelligent alright.

If you can't match the revs to make the downshift smooth, you have no business behind the wheel. There's much less risk of locking the wheels when you downshift than there is by using the brakes and you maintain more control even than ABS.

ZV

I'm going to have to strongly disagree with this. I was stuck in the snow with my Z, and I tried to downshift. Huge mistake. Since the rear end lost traction while the front end still had a slight bit of traction, the rear end would come around on me. On the other hand, when I used the brakes, all the wheels would be modulated by the ABS and the car stayed pointed in the right direction.

Not only couldn't I downshift, I couldn't even let off the gas when the car was in gear. If I wanted to lift off the gas, I had to push in the clutch.

Summer performance tires really suck in snow. My car would break traction if I put it in 5th gear from a dead stop and did nothing other than let out the clutch. No gas needed, the wheels would spin simply from the engine trying to maintain idle speed. It is horrible in the snow.

 

[Pacfanweb]

Originally posted by: 91TTZ

Originally posted by: Zenmervolt

Originally posted by: RGUN
WHAT?? So you're driving along an icy road and you need to slow down, apply brakes and use all the wheels and the ABS safety net OR downshift to a lower gear therefore making power application much less smooth and risk locking the wheels? yeah thats intelligent alright.

If you can't match the revs to make the downshift smooth, you have no business behind the wheel. There's much less risk of locking the wheels when you downshift than there is by using the brakes and you maintain more control even than ABS.

ZV

I'm going to have to strongly disagree with this. I was stuck in the snow with my Z, and I tried to downshift. Huge mistake. Since the rear end lost traction while the front end still had a slight bit of traction, the rear end would come around on me. On the other hand, when I used the brakes, all the wheels would be modulated by the ABS and the car stayed pointed in the right direction.

I had a situation like this. In your scenario, it would have to be a rear wheel drive car. I was driving my old Trans Am back when I was a teenager, in the snow. I was coming down a hill, and was getting a bit faster than I wanted to go...so I dropped the trans back a gear...big mistake. The rear tires locked up, and the ass end started fish-tailing. Almost got me a date with a concrete bridge support before I got it straightened out.

So in a RWD vehicle, I would NOT recommend anyone downshift in the snow or ice. In a FWD or 4x4, downshifting will give you much better control over your vehicle, though.

 

[91TTZ]

Originally posted by: Zenmervolt

Absolutely no way it was the battery. The alternator, even at idle, puts out sufficient energy to run the engine even if the battery were removed from the car. Unless the alternator is defective as well.

Under no circumstances should a running automotive engine be dependant on the battery to remain running.

ZV

That used to be the case, but not any longer. It's a PITA.

On my cars, I can jump the car and let it run off the alternator alone. But on a friend's car, it simply will not run without a battery present. It won't even try to run. I think that the ECU can detect that there's no battery present and stop the engine from running.

 

[spidey07]

Originally posted by: Pacfanweb
I had a situation like this. In your scenario, it would have to be a rear wheel drive car. I was driving my old Trans Am back when I was a teenager, in the snow. I was coming down a hill, and was getting a bit faster than I wanted to go...so I dropped the trans back a gear...big mistake. The rear tires locked up, and the ass end started fish-tailing. Almost got me a date with a concrete bridge support before I got it straightened out.

So in a RWD vehicle, I would NOT recommend anyone downshift in the snow or ice. In a FWD or 4x4, downshifting will give you much better control over your vehicle, though.

Ever play with a all-wheel drive or 4x4 in the snow or really slippery conditions?

That's the misnomer - that downshifting is a good thing. Without a very experienced driver it can cause one to lose traction ON ALL 4 WHEELS. The only answer to this is to give a good amount of throttle of course but that goes against all logic of those that can't drive.

There are other people that read this thread. Please don't encourage downshifting in slippery conditions, it is only to be done by experienced drivers. This manuever can send a newbie totally out of control.

 

[exdeath]

Originally posted by: spidey07

Originally posted by: Pacfanweb
I had a situation like this. In your scenario, it would have to be a rear wheel drive car. I was driving my old Trans Am back when I was a teenager, in the snow. I was coming down a hill, and was getting a bit faster than I wanted to go...so I dropped the trans back a gear...big mistake. The rear tires locked up, and the ass end started fish-tailing. Almost got me a date with a concrete bridge support before I got it straightened out.

So in a RWD vehicle, I would NOT recommend anyone downshift in the snow or ice. In a FWD or 4x4, downshifting will give you much better control over your vehicle, though.

Ever play with a all-wheel drive or 4x4 in the snow or really slippery conditions?

That's the misnomer - that downshifting is a good thing. Without a very experienced driver it can cause one to lose traction ON ALL 4 WHEELS. The only answer to this is to give a good amount of throttle of course but that goes against all logic of those that can't drive.
There are other people that read this thread. Please don't encourage downshifting in slippery conditions, it is only to be done by experienced drivers. This manuever can send a newbie totally out of control.

To keep a MR2 from spinning you keep ON the throttle, while letting off puts you in a spin. Funny how that works. 99% of most peoples instant reaction is let off the thottle (which is usually correct in front engine rear wheel drive cars) or worse, hit the brakes (pretty much always incorrect)

 

[gsellis]

"Grasshopper, when you can downshift without using the clutch, it will be time for you to leave."

 

[palindrome]

Originally posted by: IGBT

Originally posted by: waggy
red makes the car faster!

..makes it easier for the cops to see.

dont remind me

 

[herm0016]

Originally posted by: Pacfanweb
Ha, nitrogen in tires.

What a complete load of B.S. that is. Does absolutely nothing but inflate the tire.

This may have been covered, but nitrogen expands a lot less under temperature. when you are going down the road the pressure in your tires gets higher due to the higher temperature. it will help tire wear in normal highway driving conditions. when racing we always use nitrogen because we have more control of the pressure in each tire and can adjust it to the track conditions.

 

[Paperdoc]

herm0016 says "nitrogen expands a lot less under temperature". I'm presuming the comparison is pure nitrogen vs. air, which is 78% nitrogen and 20% oxygen. Now from a purely theoretical standpoint, both nitrogen and oxygen are linear diatomic molecules and one would expect their thermal capacities to be very similar. One might also expect their thermal expansion coefficients in the range of 20 to 50 C and 2 to 3 atmopheres pressure to be very similar (even though I recognize that neither is truly an "ideal gas"). So I don't see how the pressure - vs. - temperture curve for pure nitrogen can be significantly different from air. Unfortunately, I could not lay my hands on actual measured data to check this out.

 

[Ktulu]

Originally posted by: mugs

Originally posted by: RGUN

Originally posted by: Pacfanweb

Originally posted by: mugs

Originally posted by: RGUN

Originally posted by: broon
Tailgate down gives you better gas mileage.

Tailgate down would reduce the drag obviously (unless you had a cap or something). Reduced drag = decreased power required --> less power required means less fuel consumption. See where Im going here?

Except you're wrong. Tailgate down doesn't decrease drag, it increases drag. I'm not a scientist so excuse my non-scientific language, but the air swirling around in the bed of the truck basically creates a "bubble" that the air going over the truck flows over.

I can attest to the fact that tailgate down doesn't help.....I have a full size Chevy drag truck. I tried it multiple times at the 1/4 mile track...tailgate up and down. Made absolutely no difference in ET or MPH. So it stands to reason that it wouldn't help mileage.

I stand correct, perhaps if you put a spoiler on the back of the cab (a la Subaru WRX) it would direct some air downward and develope Laminar flow out the back of the bed?

I have no idea, but a tonneau cover is supposed to be the most aerodynamic.

This is absolutely true. My 5.3L Silverado is rated at 19 mpg highway, but I regularly get 23-25mpg hwy with my tonneau cover on.

 

[Pacfanweb]

Originally posted by: herm0016

Originally posted by: Pacfanweb
Ha, nitrogen in tires.

What a complete load of B.S. that is. Does absolutely nothing but inflate the tire.

This may have been covered, but nitrogen expands a lot less under temperature. when you are going down the road the pressure in your tires gets higher due to the higher temperature. it will help tire wear in normal highway driving conditions. when racing we always use nitrogen because we have more control of the pressure in each tire and can adjust it to the track conditions.

You simply don't understand why race teams started using nitrogen. It was convenient. They already had it on hand to run their tools. It is now just an old mechanic's tale that it helps with air pressures.
Nitrogen is not more effective than regular air at holding pressure. You're already breathing right at 80% nitrogen. Nitrogen systems that dealers and shops have supposedly gets that percentage up to about 90-95. The systems I've seen usually claim they are putting in 92-93%.
That is a negligible amount, even if it did help...which is doesn't.
Your tires already allow for the expansion of the air inside. That's why the manufacturer specifies a particular pressure.
And it's BS that they hold pressure better when cold, too. I've already proven my buddies at a couple of dealerships wrong on that one. Went outside with a few cars that had nitrogen and a few that had regular air on a nice crisp morning, and they were all exactly the same.
Go here for some real details from people that know a lot more about engineering than the majority of us do.

 

[feralkid]

Originally posted by: Pacfanweb

Originally posted by: herm0016

Originally posted by: Pacfanweb
Ha, nitrogen in tires.

What a complete load of B.S. that is. Does absolutely nothing but inflate the tire.

This may have been covered, but nitrogen expands a lot less under temperature. when you are going down the road the pressure in your tires gets higher due to the higher temperature. it will help tire wear in normal highway driving conditions. when racing we always use nitrogen because we have more control of the pressure in each tire and can adjust it to the track conditions.

You simply don't understand why race teams started using nitrogen. It was convenient. They already had it on hand to run their tools. It is now just an old mechanic's tale that it helps with air pressures.
Nitrogen is not more effective than regular air at holding pressure. You're already breathing right at 80% nitrogen. Nitrogen systems that dealers and shops have supposedly gets that percentage up to about 90-95. The systems I've seen usually claim they are putting in 92-93%.
That is a negligible amount, even if it did help...which is doesn't.
Your tires already allow for the expansion of the air inside. That's why the manufacturer specifies a particular pressure.
And it's BS that they hold pressure better when cold, too. I've already proven my buddies at a couple of dealerships wrong on that one. Went outside with a few cars that had nitrogen and a few that had regular air on a nice crisp morning, and they were all exactly the same.
Go here for some real details from people that know a lot more about engineering than the majority of us do.

What kind of tools were run on Nitrogen?




T.I.A.

 

[Zenmervolt]

Originally posted by: Pacfanweb

Originally posted by: 91TTZ

Originally posted by: Zenmervolt

Originally posted by: RGUN
WHAT?? So you're driving along an icy road and you need to slow down, apply brakes and use all the wheels and the ABS safety net OR downshift to a lower gear therefore making power application much less smooth and risk locking the wheels? yeah thats intelligent alright.

If you can't match the revs to make the downshift smooth, you have no business behind the wheel. There's much less risk of locking the wheels when you downshift than there is by using the brakes and you maintain more control even than ABS.

ZV

I'm going to have to strongly disagree with this. I was stuck in the snow with my Z, and I tried to downshift. Huge mistake. Since the rear end lost traction while the front end still had a slight bit of traction, the rear end would come around on me. On the other hand, when I used the brakes, all the wheels would be modulated by the ABS and the car stayed pointed in the right direction.

I had a situation like this. In your scenario, it would have to be a rear wheel drive car. I was driving my old Trans Am back when I was a teenager, in the snow. I was coming down a hill, and was getting a bit faster than I wanted to go...so I dropped the trans back a gear...big mistake. The rear tires locked up, and the ass end started fish-tailing. Almost got me a date with a concrete bridge support before I got it straightened out.

So in a RWD vehicle, I would NOT recommend anyone downshift in the snow or ice. In a FWD or 4x4, downshifting will give you much better control over your vehicle, though.

Did it all winter with my Mustang. It's pretty easy to match RPM to wheelspeed. You simply shift, bring up the revs before engaging the clutch, and slowly release it. Then, after changing gears, you let off the throttle. No wheelspin. Sure, if you dump the clutch into the lower gear you'll break traction, but you shouldn't be doing that.

Should NOT be done with an automatic, because that will just slam into gear without rev-matching, but on a manual you should be able to match RPM with wheelspeed for the selected gear.

If you invoke ABS, you've already screwed up. I've never had ABS kick in on anything but a panic stop, even in snow or on ice. ABS should not be modulating your braking, even in bad conditions.

ZV

 

[Pacfanweb]

Originally posted by: feralkid

What kind of tools were run on Nitrogen?
T.I.A.

Screwdrivers, obviously.


Air tools

 

[feralkid]

Originally posted by: Pacfanweb

Originally posted by: feralkid

What kind of tools were run on Nitrogen?
T.I.A.

Screwdrivers, obviously.


No need to get snippy, I was just curious.


Air tools

What's the advantage of using nitrogen?

 

[91TTZ]

Originally posted by: Zenmervolt
Did it all winter with my Mustang. It's pretty easy to match RPM to wheelspeed. You simply shift, bring up the revs before engaging the clutch, and slowly release it. Then, after changing gears, you let off the throttle. No wheelspin. Sure, if you dump the clutch into the lower gear you'll break traction, but you shouldn't be doing that.

Should NOT be done with an automatic, because that will just slam into gear without rev-matching, but on a manual you should be able to match RPM with wheelspeed for the selected gear.

If you invoke ABS, you've already screwed up. I've never had ABS kick in on anything but a panic stop, even in snow or on ice. ABS should not be modulating your braking, even in bad conditions.

ZV

If I gave you the keys to my Z in the snow, there is a 100% chance that you'll be sliding all over the place. There is no traction at all. None. Rev matching is useless because the wheels would still spin. There isn't a chance that the car is drivable in the snow with the tires I have on it.

My car wouldn't make it up my driveway, which isn't even hilly. It also wants to fall down the slope of the road, so you end up on the side of the street. As soon as you start moving, the tail end falls down the crown of the road. Put it this way- there is so little traction that 5th gear still spins from a dead stop with little to no gas required.

The fact that you were able to drive your Mustang all winter tells me that it's much more manageable than my car. Trust me, it's unbelievably bad. There are some things that you must experience first hand to believe.

 

[mrSHEiK124]

Originally posted by: 91TTZ

Originally posted by: Zenmervolt
Did it all winter with my Mustang. It's pretty easy to match RPM to wheelspeed. You simply shift, bring up the revs before engaging the clutch, and slowly release it. Then, after changing gears, you let off the throttle. No wheelspin. Sure, if you dump the clutch into the lower gear you'll break traction, but you shouldn't be doing that.

Should NOT be done with an automatic, because that will just slam into gear without rev-matching, but on a manual you should be able to match RPM with wheelspeed for the selected gear.

If you invoke ABS, you've already screwed up. I've never had ABS kick in on anything but a panic stop, even in snow or on ice. ABS should not be modulating your braking, even in bad conditions.

ZV

If I gave you the keys to my Z in the snow, there is a 100% chance that you'll be sliding all over the place. There is no traction at all. None. Rev matching is useless because the wheels would still spin. There isn't a chance that the car is drivable in the snow with the tires I have on it.

My car wouldn't make it up my driveway, which isn't even hilly. It also wants to fall down the slope of the road, so you end up on the side of the street. As soon as you start moving, the tail end falls down the crown of the road. Put it this way- there is so little traction that 5th gear still spins from a dead stop with little to no gas required.

The fact that you were able to drive your Mustang all winter tells me that it's much more manageable than my car. Trust me, it's unbelievably bad.

Waaaaaait a minute, 91TTZ = 1991 Twin Turbo 300ZX?

 

[91TTZ]

Originally posted by: mrSHEiK124

Originally posted by: 91TTZ

Originally posted by: Zenmervolt
Did it all winter with my Mustang. It's pretty easy to match RPM to wheelspeed. You simply shift, bring up the revs before engaging the clutch, and slowly release it. Then, after changing gears, you let off the throttle. No wheelspin. Sure, if you dump the clutch into the lower gear you'll break traction, but you shouldn't be doing that.

Should NOT be done with an automatic, because that will just slam into gear without rev-matching, but on a manual you should be able to match RPM with wheelspeed for the selected gear.

If you invoke ABS, you've already screwed up. I've never had ABS kick in on anything but a panic stop, even in snow or on ice. ABS should not be modulating your braking, even in bad conditions.

ZV

If I gave you the keys to my Z in the snow, there is a 100% chance that you'll be sliding all over the place. There is no traction at all. None. Rev matching is useless because the wheels would still spin. There isn't a chance that the car is drivable in the snow with the tires I have on it.

My car wouldn't make it up my driveway, which isn't even hilly. It also wants to fall down the slope of the road, so you end up on the side of the street. As soon as you start moving, the tail end falls down the crown of the road. Put it this way- there is so little traction that 5th gear still spins from a dead stop with little to no gas required.

The fact that you were able to drive your Mustang all winter tells me that it's much more manageable than my car. Trust me, it's unbelievably bad.

Waaaaaait a minute, 91TTZ = 1991 Twin Turbo 300ZX?

Yeah, that's me.

Text

 

[Pacfanweb]

Originally posted by: feralkid

Originally posted by: Pacfanweb

Originally posted by: feralkid

What kind of tools were run on Nitrogen?
T.I.A.

Screwdrivers, obviously.


No need to get snippy, I was just curious.


Air tools

What's the advantage of using nitrogen?

In what...tools or tires? For tires...no advantage. For the tools, it was a source of compressed gas to run the tools.
I think most folks nowadays would use CO2 instead. Much more potential stored in a bottle of that.

 

[mrSHEiK124]

Originally posted by: 91TTZ

Originally posted by: mrSHEiK124

Originally posted by: 91TTZ

Originally posted by: Zenmervolt
Did it all winter with my Mustang. It's pretty easy to match RPM to wheelspeed. You simply shift, bring up the revs before engaging the clutch, and slowly release it. Then, after changing gears, you let off the throttle. No wheelspin. Sure, if you dump the clutch into the lower gear you'll break traction, but you shouldn't be doing that.

Should NOT be done with an automatic, because that will just slam into gear without rev-matching, but on a manual you should be able to match RPM with wheelspeed for the selected gear.

If you invoke ABS, you've already screwed up. I've never had ABS kick in on anything but a panic stop, even in snow or on ice. ABS should not be modulating your braking, even in bad conditions.

ZV

If I gave you the keys to my Z in the snow, there is a 100% chance that you'll be sliding all over the place. There is no traction at all. None. Rev matching is useless because the wheels would still spin. There isn't a chance that the car is drivable in the snow with the tires I have on it.

My car wouldn't make it up my driveway, which isn't even hilly. It also wants to fall down the slope of the road, so you end up on the side of the street. As soon as you start moving, the tail end falls down the crown of the road. Put it this way- there is so little traction that 5th gear still spins from a dead stop with little to no gas required.

The fact that you were able to drive your Mustang all winter tells me that it's much more manageable than my car. Trust me, it's unbelievably bad.

Waaaaaait a minute, 91TTZ = 1991 Twin Turbo 300ZX?

Yeah, that's me.

Text

Dude, I love your car :heart: