So, I'm pretty sure this spark plug isn't supposed to look like this after only 3000 miles, no? Not quite sure what's going on, but the ashy substance flicks right off with a knife easy enough. This was the worst cylinder, #3, but the others had it too. It's a wonder they were firing at all.

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Find out exactly what you're using for fuel, and what's in it.
Looks like fuel deposits to me, but I'm no expert.

Roger

Just regular old E10 from QuikTrip, but now that you mention it I did run some Marvel Mystery Oil through it last Spring. Could that cause those kind of deposits? I thought that stuff was supposed to clean things up.

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It looks a bit too big and crunchy to be a likely candidate for fuel additive deposits. And is it just this one plug that looks like that? Because if it were fuel additive deposits, it wouldn't be limited to the one plug. And if it were just plain fuel deposits, i.e., running too rich, it would be black and fluffy. And if it were oil deposits, i.e., burning oil, it would be black and shiny/sticky.

This what we're looking at has the right colour, mass, and appearance to be silica deposits, which comes from burning coolant (which contains sodium silicate and other silicate-based corrosion inhibitors), and that can be a just-one-cylinder thing, in the event of a head gasket leak or a cracked casting.

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一期一会
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Well that doesn't sound good! But like I said earlier, this is the worst one, but all had some of this stuff to varying degrees. I haven't seen any "milkshake" in the oil though.

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Yes, I agree with Dan, and another source is a leaky manifold stud. Recall, recently mine were leaking and the coolant was literally getting sucked between the gasket and head/manifolds and into the intake ports. No coolant in the oil, just going from the water jacket to the intake port via the leaky studs.

Do you have any signs of coolant leaks below the exhaust manifold on the side of the block?

brian

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You only get that if the head gasket is letting coolant seep into the crankcase. It's fairly common for a bad H/G to first manifest as seepage into the cylinders. Symptoms include misfire on startup (for a minute or so), white smoke out the tailpipe, low coolant level in the radiator (do you have to top up the level?)

Very minor seeps can cause deposits like you have. If it gets worse the coolant can "steam clean" the plug & combustion chamber. A good way to check things out is to get a pressure tester, heat up the engine, then use the tester to pressurize the cooling system & let it sit overnight. Next day, yank the plugs & check for coolant in the cylinders.

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63 Valiant Wagon
225 - 4 bbl

Check for coolant leaks under the manifold at the intake port for the cylinder that plug came from. My engine had no head gasket leak (fresh rebuild) but the manifold studs were leaking and the vacuum from the intake stroke was pulling the coolant into the cylinder via the intake port, literally sucking it between the manifold gasket and the head. I was getting excess water in the exhaust effluent, and I thought my head gasket might have been leaking, but not so. My plugs had similar buildup.

brian

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So far I haven't noticed any extra coolant loss, not any external evidence of leaking under the manifold. But this does warrant further investigation.

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Some of mine were leaking enough to see drips below the manifold, but others showed no signs, but when I pulled the manifolds, there was a clear path where the coolant went from the base of the stud and into the intake port via suction. Check out this photo:

http://s785.photobucket.com/user/67dart ... 0.jpg.html

Notice the third stud from the left, the one on top. See those brown stains? Those are the coolant trails. The #4, #5 and #6 intake ports were sucking leaking coolant directly in (you can see the exhaust ports were blowing it outward) between the gasket and the head. I was using a Remflex gasket and it was soaked with coolant (that's why I didn't see the leak for awhile, it was soaking up the extra coolant until it got saturated). The only signs below the manifolds were under #4, those coolant stains below the head came after I pulled the manifolds and the leaky coolant ran down and stained (my purdy) paint job.

Brian

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Thanks for the input. I think the next time I have a couple days off I might pull the manifold and check. I bet that's what is causing the problem.

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