How does water get into the coil pack?

[JEDI]

2005 mazda3i AT, 200k miles

From this thread about my car almost stalling at red light on a rainy day:
http://forums.anandtech.com/showthread.php?t=2410192

Some people have suggested that water in the coil pack might be the reason.

yes, I drove thru some puddles that day at hwy speeds.
but I've had my car for 200k miles and I have driven in rain/puddles often.

Now I'm curious.
how does water get into the coil pack?

 

[Hail The Brain Slug]

Bad luck? Worn seals? cracked casing? Deeper than average puddles?

 

[JEDI]

Deeper than average puddles?

my car has a plastic skid plate that covers the bottom of the engine.

so the water has to splash thru the small openings in the skid plate and spaces inbetween the engine parts to land on top of the engine, and drip down into the spark plug compartment?

 

[Meghan54]

So you think water cannot enter small openings? Really? I doubt your "skid plate", as you put it, is water tight, so certainly water can get by that air deflector underneath your engine compartment. (Skid plates aren't plastic, but air deflectors are. )

 

[JEDI]

so if it was water that caused my car to almost stall while stopped at a red light, then it should be fine if I left the car alone for, say, 3 days?

enuf time for the water to evaporate?

wait.. the water should have evaporated on day 1 because of the hot engine?!

 

[JCH13]

The insulation around the coil pack will degrade over time. So do seals, potting compounds, joints, seams, etc.

Imagine this: you're driving on the interstate for a while, everything is getting nice a toasty in the engine compartment. What little gas (as in air, not fuel) is inside the coil, in the plug well, etc is hot and expands and leaks out around degraded seals. You pull of the interstate and drive slowly for a while and everything cools down. Air is sucked back into those locations as things cool off, and water is sucked in too, if it is present. This shorts out the plug, coil, etc.

As I said above, the insulation will degrade over time, possible to the point of allowing electricity to leak out of the coil. When the coil gets wet, or there is moisture near it, there is enough of a path for some (or all) of the spark energy to get out right through the insulation. The voltage in a coil can get somewhere the neighborhood of 30k volts, this requires a good bit of quality insulation to contain. If you've gotten 200k out of your original coils you've done REALLY well.

 

[SparkyJJO]

If there is water around the pack or down the plug well you may just be able to dry it out and be OK. My Trailblazer has a bad hood seal design (early one was flawed) that sometimes lets water around it in really heavy rains, which twice since I've had the truck has gotten water down around the spark plug directly below and shorted the plug. Both times I dried out the plug well and coil and moved on. 204k on original coils

Ideally you find the leak and FIX it, not just sop it up and keep going, but I keep forgetting to do anything about it and it rarely happens (only twice in 4 years)

 

[waffleironhead]

Bad gaskets and condensation.

 

[JEDI]

while cleaning throttle body, I decided to check on coilpacks/sparkplugs.

all coil packs + spark plugs dry.

 

[Pacfanweb]

The answer is easy: Do you think you could put a paper towel on top of your engine, then drive through the rain and it would remain dry?

The correct answer is, no, it would not remain dry.