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in a stock situation, how hot is it roughly in the engine bay, on a hot summers day, say 30C .

I'm just asking cause I need to put some wires in there and I'm wondering which type of wiring would be best to withstand the heat and Canadian cold.
 

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Just get a set of stock ones either from a local dealership or online...
 

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It depends on where you run your wires. Close to the exhaust, really hot, just about any where else, not so much. I did a bit of custom wiring in my setup and have not had a melting issue yet, I just made sure that the wires do not touch anything that could get really hot. I don't think that you could generate enough heat to melt wires under the hood with out them being really close to something that obviously gets really hot.
I would just use some decent automotive wiring that you can get in any auto parts store, and keep it away from the exhaust manifolds and heater lines and you should be fine. I also like to wrap wiring in wire loom to help protect it.
 

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Use automotive electrical wire, not house stuff. As long as you don't zip tie it to the exhaust manifolds you will be fine (j/k). Common sense is king here, keep the wires away from really hot stuff ie exhaust manifolds, there is a lot of wire under the hood already. If you want to keep it clean, orderly, and protect it a little put wire loom around it.
 

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I should have read the question better on what kind of wires you wanted to run...

As the others have said... As long as you stay away from the exhaust you will be fine.
 

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It can get up to around 125-135*F under the hood. I have CAI and at a stand still with the engine warmed up, my IAT is around 120*F. This is when it is just over 80*F outside. When I get moving or go WOT, my IAT drops to ambient air temperature.
 

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Use automotive electrical wire, not house stuff. As long as you don't zip tie it to the exhaust manifolds you will be fine (j/k). Common sense is king here, keep the wires away from really hot stuff ie exhaust manifolds, there is a lot of wire under the hood already. If you want to keep it clean, orderly, and protect it a little put wire loom around it.

Ya no doubt, I seen the way ford does it, cover it with wire loom, then wrap a 2' section with 75 rolls of electrical tape.

My biggest concern is how the heat and cold affect the insulation over time. I wanted to make sure I could get some wire able to withstand the temps, but will also last for MANY years.

I'm not entirely sure if I will be able to loom this wire the way I need to wire it up, and I didn't want the insulation going dry and cracking after like a year. It's only small wire I need, like 16 or 18awg, and only like 4 wires. 2 to my battery and two to my alt. (it's for gauges/meters)


thats crazy with the thermometer.... it's pretty hot. There is wrap I can get for my manifold to keep it cooler in the engine bay is there not? not that I'm looking at doing this anytime soon, but removing the exhaust manifolds is a real pain in the ass isn't it?
 

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Most wire (THHN) will be just fine at 160*F. If exceed 190* then could have issue but really only the current capacity drops.
 

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I use Teflon, type EE mil grade; good to over 200C, 400C to burn off.

Just don't pull the wireties too tight, lol.

bowez, I've never known the current carrying capability of wire to decrease with temperature, just the insulation degrades... :confused:

Just don't use solid wire, it will break from vibration.
 

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and ... As resistance rises, so does heat.

:D

I've used wire from automotive supply outlets / speed shops / NAPA / etc my whole life of working on my cars and bikes, right at 40 years now.

Never had issues with heat except when they come in contact with exhaust manifolds or headers, and then it was someone elses doings that allowed the contact.

Anywhere else under the hood and wire insulation melts, you have a short or electrical overload on a unfused or improperly fused wire ...
... and a fire of some description usually.
 

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I use Teflon, type EE mil grade; good to over 200C, 400C to burn off.

Just don't pull the wireties too tight, lol.

bowez, I've never known the current carrying capability of wire to decrease with temperature, just the insulation degrades... :confused:

Just don't use solid wire, it will break from vibration.
Not to be a smartas, but NEMA has a table just for that. As long as you stay under or at 90*C insulation will be ok (for THHN). I list THHN because its the most common.
 

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Not to be a smartas, but NEMA has a table just for that.
Good, cause that's not what that table says. :D

You have to 'Derate', or lower, the amount of current you run thru a wire at higher temperatures; it won't lower the current for you, it will catch on fire. (as CrystalPistol said)

The resistance does rise with temperature, but not enough to matter to the copper wire (or the circuit) over any temperature you will run into on a car.

Copper wire in a vacuum can go incandescent and not lose current carrying capability; as long as it doesn't short to something it's fine. I've built equipment that did that, but we weren't using copper wire; Iridium wire lasts longer. The resistance increase actually helps a bit, as it acts as negative feedback; at ~900C copper is a good resistor... but I digress. :rolleyes:


The additional temperature rise due to self-heating in combination with the ambient temperature causes the insulation to melt, then a short to form; that's the problem, and the reason for a chassis wiring rating and a bundle wiring rating in the code book. (if a bunch of wires are close together, like a cable or wiring harness, they will get hotter from shared heat and a reduced cooling area, making them melt easier)

If anyone care, here's a link to a decent sizing table for wiring; there's a table at the bottom for teflon based on a 70C ambient; that's a reasonable max temperature under a hood. A search will find a table for other insulators.

http://www.interfacebus.com/Reference_Cable_AWG_Sizes.html

There is some good additional info in the notes at the bottom.



Bowez, I guess maybe you were talking about the insulation, but I didn't read it that way. :zdunno:

If you worry about the ambient temp + self heating being too much, use a bigger diameter wire; less self-heating from the current... :)
 

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Good, cause that's not what that table says. :D

You have to 'Derate', or lower, the amount of current you run thru a wire at higher temperatures; it won't lower the current for you, it will catch on fire. (as CrystalPistol said)

The resistance does rise with temperature, but not enough to matter to the copper wire (or the circuit) over any temperature you will run into on a car.

Copper wire in a vacuum can go incandescent and not lose current carrying capability; as long as it doesn't short to something it's fine. I've built equipment that did that, but we weren't using copper wire; Iridium wire lasts longer. The resistance increase actually helps a bit, as it acts as negative feedback; at ~900C copper is a good resistor... but I digress. :rolleyes:


The additional temperature rise due to self-heating in combination with the ambient temperature causes the insulation to melt, then a short to form; that's the problem, and the reason for a chassis wiring rating and a bundle wiring rating in the code book. (if a bunch of wires are close together, like a cable or wiring harness, they will get hotter from shared heat and a reduced cooling area, making them melt easier)

If anyone care, here's a link to a decent sizing table for wiring; there's a table at the bottom for teflon based on a 70C ambient; that's a reasonable max temperature under a hood. A search will find a table for other insulators.

http://www.interfacebus.com/Reference_Cable_AWG_Sizes.html

There is some good additional info in the notes at the bottom.



Bowez, I guess maybe you were talking about the insulation, but I didn't read it that way. :zdunno:

If you worry about the ambient temp + self heating being too much, use a bigger diameter wire; less self-heating from the current... :)
I just posted the resistance thing cause it was brought up, I didn't think the engine bay would be hot enough to cause issues, however I am working with mV power, so if there is going to be a slight change in voltage due to heat, even small, it may affect the meters I'm working with.

I don't think it should cause an issue though, I just didn't want crumbly wires after 2 years or something.
 

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Here's some figures from Texas. But in F not C. Hot day, 95F day.Engine water temp was going as high as 216F and ambient was 96 while moving. Red light and sitting in sun idle temp rose to 164 F. Yes, to the Yankee's wondering if I was using the A/C. Using cone K&N filter mounted as close to front as possible. These reading were taken from a scanGauge.
 

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I just posted the resistance thing cause it was brought up, I didn't think the engine bay would be hot enough to cause issues, however I am working with mV power, so if there is going to be a slight change in voltage due to heat, even small, it may affect the meters I'm working with.

I don't think it should cause an issue though, I just didn't want crumbly wires after 2 years or something.
The error in the reading is proportional to the resistance of the wires in relation to the resistance of the meter...

I just built a voltmeter at work, and the meters were 350 ohms; I used 20awg wire, which is (from the table, linked above) 10.35 ohms per 1000ft.

10.35/1000=.01035 .01035*10 ft (2x 5 foot runs; out and back) = .1035 ohms

.1035/350=.0002957, or .03% error.

From this site;
http://www.allaboutcircuits.com/vol_1/chpt_12/6.html

The temperature change to 100C (boiling water) causes the wires in the above example to be .136959 ohms from .1035... .136959/350=.000391, or almost .04% error.

That's well within the accuracy of the meter itself (~1% is an expensive meter these days); after nulling the meter setting, zeroing out the .03% error (lol!), (adjusting the meter zero) the change due to temperature is only .01% over a 75C range.

See why I said the wire doesn't change appreciably?

Copper melts at about 1100C; at 1100C the resistance is .513 ohms; which is a .15% error in the above described circuit... :)

I'm on my first cup of coffee, but even if I blew a decimal point there somewhere, it shouldn't matter; the errors are small. :rolleyes: If I did, point it out and I'll fix it.

The most critical meter for wiring is an Ammeter hookup; keep the shunt as close to the battery as possible, and use wire bigger than the battery cables for the heavy current connections.

Teflon never hardens; but over 200C it evaporates, and the HF it releases eats stuff. But if your car goes over 200C, everything else is fried anyway, lol.

YMMV.
 

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Grog, I was unclear in my post I was referring to the capacity drop tables.

But I still stand by my opinion that THHN is just fine for automotive and if its not for your (not you Grog) application you better know what your doing.
 
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