Dirty Coil and Spark Well

I went to change my spark plugs today at 63k or so, and was surprised to see the middle coil on the passenger side was very dirty.

I also noticed my coolant, which has not been serviced, is a bit below the Low line. Not sure if related, but figured I’d mention it.

I put everything back in place and did not yet swap the plugs. I am not familiar enough to know what the problem could be, did some searching but didn’t find a perfect answer.

Any suggestions where to go from here, or what to check? See attached pics. The coil appeared moist when I removed it, but dried up quick.

 

Was the plug torqued properly ?

 

Classic sign of loose spark plug.

 

I did not check the torque, just wiped it down and reinstalled the coil for now. I will pop it back out and check.

They have not been touched since the factory, but I can certainly imagine it was not torqued properly. Thanks

 

toyota is notorious for under-torquing things from the factory

 

I don’t see anything with dirt on it in your picture. The middle coil looks to be corroded, burnt, or have some other sort of surface damage or contaminate.

What does the spark plug look like?

 

Loose sparkplug from the factory.

 

Loose spark plug or a loose coil pack allowing water in? How does a loose spark plug result in what looks like rust? I’m just curious. Not arguing.

 

Its a known issue on the 3.5 to have a loose plug or two, blowby discolors the coil.

Loose Spark Plug From The Factory | Tacoma World

 

Don't think it's rust. Looks like oil that's been baked on.

 

The coil in the first post looks quite different than the one above. OP, it would be interesting to see the spark plug and other observations like presence of water, what effect wiping off the coil off had, how tight the plugs were, etc. It should have been quite obvious if one plug was loose.

EDIT: on page 7 there is a coil that looks more similar to the OP’s and the poster also mentioned that the plug was obviously loose. I do not know what material the coil pack is made of. I suppose there could be a chemical reaction between it and blow by gasses to cause the reddish brown color, but I have no idea what.

 

Here’s a wild guess… blow by from a loose spark plug caused the coil pack seal to come loose allowing water in and that caused rusting of the coil pack. This assumes the coil pack material is ferric.

 

Loose spark plug causing blowby for sure. Lots of threads about it. Torque the new plugs properly and no big deal.

 

Went back and swapped them all today. The one in question was jiggly loose, required no force to turn out.

The others were OK.

Thank you all for the advice