Spark plugs fouled on the first start after piston soak, replace or clean?

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PandaBear

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B12 chemtool about 1/4 bottle per cylinder, soaked for 24 hours, then hand cranked and starter cranked with plugs out to remove as much fluid as possible.

Took quite a long time to start the engine, pull the plugs out to check and found that 3 of the 4 plugs are completely covered with black carbon. Maybe I really have that much deposit that got freed up in 29 years and 280k miles.

I searched through my garage and found some odd left over plugs that Rockauto says would work. 3 Champion double plat (brand new) and 2 Bosch +4 (slightly used), and the not fouled old Champion single plat (about 30k, the platinum disk is still on but the steel edges around it has eroded slightly).

So right now I have 3 new Champion double plat and 1 Bosch +4 in there, I can probably clean all 4 Champion single plat and just put them back in, or just keep driving 3 champion double plat and buy 1 more champion double plat to match.

Or just buy all new NGK copper (OEM) and be done with it.

What would you do?
 
When I did the piston soak on my sons Kia Rio, I left the old plugs in until the next oil change. Then replaced them. The plugs only had about 15K on them. I cleaned them off (They never looked bad to be honest) and used them for another oil change. My plan was to change them right away and I was going to the following weekend, but plans changed and I didn't get to it, so just let him motor on another 4-5K. Changed them after that. They looked fine when I took them out after the next oil change. Car didn't burn a drop of oil. I changed them anyway, but really didn't need to....

I would encourage you to just look them over and make sure they're clean and properly gapped. Also, wouldn't hurt to just swap them. YMMV.
 
A 29 year old car with 280,000 miles? If the engine runs with what you have in it now, let them in and drive the car for a couple of months. Do some high speed runs. Take a trip. You may break loose some more crud that could foul a plug and why do that to a new plug. At the end of that time, change them for new plugs.
 
melk said:
Pics!
Click to expand...
In the trash already but this is about how 3 of the 4 looks like:

1775533028984.webp
 
ripcord said:
Wow. I haven't ever seen a plug that dark since carburetors were the norm.
Click to expand...
It was actually worse now that I think of it. They were super clean before the piston soak, but I think a few bigger pieces of carbon was lodged in between the insulator and the metal "tube" where the threads were on.

Was thinking about cleaning them with half a can of B12 chemtool, but then again it is probably not worth all the fume I would be inhaling for some half worn (already 30k on it) platinum plugs that was Champion on Honda. If I were going to be cheap I could just buy some $4 platinum Champion / Autolite / Bosch or $6 Denso / NGK. I got those on rebate for $2 each from probably 15 years ago.
 
I've hot soaked pistons and valves many times over the years and I've never had one foul the plugs. Atf works better than B12. I would say that your cats are pretty dirty with that much oil burning.
 
Fwiw, I had worse buildup on my spark plugs after I did my B12 piston soak startup. You did the right thing, just throw new ones and enjoy less / or no oil burning 🍺
 
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B12 Chem soaked my Hyundai Elantra. Took a bit for it to start and run reliably. Have read that is pretty common unless you oil fog the cylinders with some fresh motor oil or even some Marvel Mystery Oil as it takes a bit for the cylinder walls to coat and make compression.

I ran my old plugs for a bit and changed them when I did the flush out engine oil change. I would not run fresh plugs on initial start after a piston soak treatment.
 
Arc said:
I've hot soaked pistons and valves many times over the years and I've never had one foul the plugs. Atf works better than B12. I would say that your cats are pretty dirty with that much oil burning.
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To be fair, the car pass smog if I do not just drive to a shop right after a cold start. If I drive around for a while after an oil change and maybe a bottle of Techron in the tank that pass with sufficient safety margin.

However I do get a shop who wants me not to bring in a car that old, and failed me once on a rainy day because of visual (he saw white cloud from the tailpipe) yet pass the numbers with no problem the next week's retest, and despite me telling him I didn't do anything. I think he was too afraid of getting dinged for not failing enough cars so he had to fail some once in a while.

This car burns about 1 quart every 1k or so before the soak on 5w30. I have recently switched to Rotella T5 15w40 and it seems to have cleaned a bit of the varnish off. I don't think it is that bad, but I think my midlife crisis is about restoring old cars instead of buying new ones. There aren't too many interesting new cars that I want recently so might as well restore old cars instead.
 
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