Fouled plugs -
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post #1 of 16 Old 08-01-2020, 01:38 PM Thread Starter
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Fouled plugs

Hi guys. Stock 258 4.2 that previous owner said he rebuilt. Since I owned it, I will get white/blue smoke from exhaust if it’s been idling and I rev the engine. Has always ran well for me. I was checking my thermostat functioning today and had it idle for about 15 minutes. When revved, blew out a lot of smoke. I pulled my spark plugs, for the first time, and found them to be in bad shape.

In the pictures, I included the two worst and the best. The other three are in between these. Also, I had a faint smoke come out of one of the spark plug holes when I pulled it. One thing to note, it sat for the better part of 9 months as I was doing the cosmetic restoration, but I have about 1500 miles on it since. Any thoughts?

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post #2 of 16 Old 08-01-2020, 03:37 PM
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Read the spark plugs. Looks kinda like oil and possibly coolant to me.

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post #3 of 16 Old 08-01-2020, 03:56 PM
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Man, I've never seen such fouled plugs before. I'm afraid it's something more than mixture/spark.

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post #4 of 16 Old 08-01-2020, 04:34 PM
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Agree it looks like a mix of oil and coolant. Cold be head gasket or bad plaining of the head before install.
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post #5 of 16 Old 08-01-2020, 04:49 PM Thread Starter
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Thanks guys. Yeah, that’s what I’m worried about. What I find crazy is that it’s ran great. I just took it on a 200 mile round trip and did great on the freeway and off-road. I read the pcv valve can contribute to the oil fouling. Do you guys see anything wrong with changing that out and putting new plugs in a driving for awhile to see how that goes?
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post #6 of 16 Old 08-02-2020, 03:01 AM
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I had oil fouled plug and switched to a different valve stem seal and they dont foul anymore. But if you have a head gasket leak that would have to be addtessed

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post #7 of 16 Old 08-02-2020, 06:16 AM
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Yes, they look pretty awful. I guess you didn't pull them when you bought the vehicle?

A new set of plugs is cheap, and you can reuse them if you have to pull the head later so...IF you THINK the head is leaking coolant into the motor do this: Run the motor to warm it up. Park it where you can leave it overnight and work on it later. Pull all 6 of the plugs. Remove the coil wire and bump the motor over. Leaking coolant will (should) puddle on the piston and blow out of the plug hole. Replace the plugs and drive for a few days then re-check.

You could also do a compression and leak-down test if you have the gauge, while you replace the older plugs.
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post #8 of 16 Old 08-02-2020, 07:31 AM
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HI since you didn't put in new plugs when you got it.. there's no telling how long or what kind of fuel the PO was using .. might have been buying cheap stuff and a cheap station.. I'd say Put in new plugs and run it for a while .. then repull them and go from there.
Don't jump to conclusions on a motor you don't really know how it was treated..
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post #9 of 16 Old 08-02-2020, 09:03 AM Thread Starter
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Yeah...not the smartest move to not pull the plugs when I bought it. My pcv seemed plugged up and I had a light coating of oil around the gasket on the valve cover. I replaced it and the plugs. I don’t have the equipment for it, but I think I’ll get a compression and leak down done so I’ll have a better idea of things.
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post #10 of 16 Old 08-02-2020, 09:07 AM Thread Starter
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On the fuel note, what fuel and company is best for the motor? I’ve always ran 87 from a variety of stations.
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post #11 of 16 Old 08-02-2020, 09:09 AM Thread Starter
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Another question...if the plugs were going to foul again, any guess at what kind of mileage it would take to show up again?
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post #12 of 16 Old 08-02-2020, 09:16 AM
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From the description i would have suspected valve stem seals and oil dripping down past the valves. You will see oil on new plugs after a few hundred miles. Check the plug number, a cooler plug than recommended would allow build up.

If it was stem oil seals, they can be changed with the head on.

Could be coolant as well, you need to leak test the engine.

it is so thick I would have assumed the combustion chamber is coked up.

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post #13 of 16 Old 08-02-2020, 09:23 AM
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HI you don't say what year it is .. so if its like a 70 or older I'd use at least Mid to HI grade.. Newer the low grade is most likely OK.. If you can find a owners manual it would tell you Octane rating suggestion.. Actually a few miles on new plugs would/should tell you how its running.. When running it .. if you drive it slowly it well show you how its running at low speeds .. if you like run it on the highway and shut it off at high RPMs (you can let it idle down but don't let it idle long before shutting it off) and check it that should show you how its running at high rpms..
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post #14 of 16 Old 08-02-2020, 10:34 AM
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post #15 of 16 Old 08-02-2020, 10:37 AM Thread Starter
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So obviously, I don’t know much, but doing some reading on valve stem seals, it sounds like it’s possible that’s my issue. I just took the Jeep to get breakfast for the kids. Sat in a long drive thru and it blows a cloud of smoke after sitting idle. Higher I rev it, the more the smoke. No smoke when driving or idling at a normal stop light. It’s always done this, but seems to be getting worse. I will get the tests done.
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